vce chemistry unit 3

VCE Chemistry Unit 3 © Ms Lanna Derry & Edrolo 2014

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Unit 3, Area of Study 1: Chemical Analysis

Gravimetric Analysis

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/chemical-analysis-gravimetric-analysis/outcome-1/#watch

CHEMISTRY



Outcome(1(

(On(completion(of(this(unit(the(student(should(be(able(to(evaluate(the(suitability(of(techniques(and(instruments(used(in(chemical(analyses.(

(

Key(Knowledge(! Gravimetric(analysis(! the(application(of(chemical(equations(to((volumetric(and)(gravimetric(analyses(



Gravimetric(analysis(

•  This(form(of(quantitative(analysis(involves(@ind(the(mass(of(a(part(of(the(sample(and(

relating(it(back(to(the(sample,(often(as(a(

percentage(by(mass(

•  The(part(of(the(sample(we(are(interested(in(may(be(the(water(in(the(product,(or(

perhaps(we(might(be(focussing(on(a(

particular(ion(that(is(present.(



Measuring(water(content(

•  Many(solids(have(a(high(proportion(of(water.(•  Dehydration(removes(the(water(and(decreases(the(mass(

•  This(may(be(heating(at(just(above(100(°C(•  Mass(loss(=(mass(of(water(originally(present(

•  %(water(content(=(m(water)(×(100((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((m(sample)(



Weigh&the&sample&

Heat&the&sample&in&an&oven&just&above&100&°C&

Allow&the&sample&to&cool&in&a&desiccator&

Reweigh&the&sample&

This cycle is repeated until the sample assumes a constant mass



Finding(the(composition(of(a(

mixture(1.  Dissolve(the(mixture(in(water(2.  Add(an(ionic(solution(which(will(

form(a(precipitate(with(the(ion(

that(is(required((eg(SO42P).(

3.  This(new(solid(is(then(@iltered(out,(dried(and(weighed.



The(most(common(precipitates&

Element'you'wish'to'analyse'

Substance'that'is'added'to'create'precipitate'

Formula'of'precipitate'

Chlorine&& Silver&nitrate& AgCl&

Bromine& Silver&nitrate& AgBr&

Sulfur& Barium&chloride& BaSO4&



Application(of(gravimetric(analysis(

!  Gravimetric(analysis(is(used(in(the(food(industry(to(determine(the(

amount(of(salt(in(products.(

! When(an(AgNO3(solution(is(added(((((((to(the(dissolved(food,(chloride(ions(((

(((((present(as(NaCl)(are(precipitated(out((((

as(AgCl.(

(&



Calculations(

Find(n(AgCl)(using:(n(AgCl)(=((

Then:&

n(AgCl)&=&n(Cl.)&=&n(NaCl)(

! Convert(n(NaCl)(to(m(NaCl)(using((((((((m(NaCl)(=(n(NaCl)(×(M(NaCl)(

(

! %(NaCl)(=(m(NaCl)(×(100(( ((((((((m(food)(((((1(

m(AgCl)M(AgCl)



Experiment((

(Analysis(of(Lawn(food(Lawn(food(contains(many(nutrients(required(by(plants(such(as(sulfate(ions,(SO4

2P,(nitrate(ions,(NO3P(and(phosphate(

ions,(PO43B.&

&

Using&gravimetric&analysis&to&;ind&the&amount&of&sulfate&ions&in&a&sample&of&lawn&food&

1.  Dissolve(lawn(food(in(water(2.  Add(barium(chloride(solution(3.  Sulfate(ions(precipitate(out(as(barium(

sulfate(((((((((((BaCl2(aq)(+(SO4

2P((aq)(→(BaSO4(s)(+(2ClP(aq)(



4.  Filter,(wash(and(dry(the(BaSO4(to(obtain(a(pure(sample(of(precipitate.(

(

5.  During(washing(stages(@iltrate(is(tested(for(presence(of(left(over(chloride(ions(by(adding(silver(nitrate.(

(AgNO3(aq)+(ClP(→(AgCl(s)(+(NO3

P(aq)(

(

•  (If(ions(are(in(the(@iltrate,(then(they(have(probably(also(stuck(to(the(solid(and(its(mass(will(be(too(high.(

((

(



6.  Barium(sulfate(is(dried,(then(weighed.((

7.  Using(M(BaSO4),(n(BaSO4)((is(calculated(so(n(SO4

2P)(can(be(deduced.((

(n(SO42P)(=(n(BaSO4)(

8.  m(SO42P)(=(n(SO42P)(×(M(SO42P)((9.  m(S)(=(n(SO42P)(×(M(S)((

10. %(S(=((m(S) 100

m(sample) 1×



Sample(exam(question(An(8.64g((sample(of(rock(was(thought(to(be(made(up(of(

CaCO3(which(reacted(with(HCl(according(to:(

2HCl(aq)(+(CaCO3(s)(→(CaCl2(aq)((+((H2O(l)(+(CO2(g)(

and(1.55g(of(insoluble(SiO2.(

(a) Calculate(the(expected(percentage(of(CaCO3(in(the(rock(sample(

(b) The(dissolved(calcium(ions(were(precipitated(out(as(CaC2O4.H2O(which(was(collected,(washed(and(dried.(It(

was(converted(to(CaO((M(=(56.1gmolP1)(and(3.87g(was(

obtained.(Calculate(the(%(CaCO3(in(the(rock(sample.(

(signi@icant(@igures)(

(VCAA(June(2007(Q3)(



(a) m(CaCO3)(=(8.64(–(1.55(=(7.09g((

(((((%(CaCO3)(=(

((

b)  n(CaO)(=(( ( (((mol(

((((((n(Ca2+)(=(0.06898(mol(=(n(CaCO3)((

m(CaCO3)(=(0.06898(×(100.1(=(6.905g(

(

%(CaCO3)(=(( ( ( ( ((

( ( ( ( ((((((((((((3(sig(@igs)(

(

(

7.09 100 82.1%8.64 1

× =

3.87 0.0689856.1

=

6.905 100 79.9%8.64 1

× =

Answers(



Xylose is a compound that has five carbon atoms in each molecule and contains 40% carbon by mass. What is the molar mass of xylose?

QUESTION 1

A. 30

B. 67

C. 150

D. It cannot be determined without further information.

(VCAA Q3 June 2008)



Xylose is a compound that has five carbon atoms in each molecule and contains 40% carbon by mass. What is the molar mass of xylose?

QUESTION 1 (ANSWER)

A. 30

B. 67

C. 150

D. It cannot be determined without further information.

Alternative C is the correct answer M(C) = 12.0 gmol-1 1 mol xylose molecules contains 5 mol C atoms (5 C atoms per molecule, so 5 mol of C atoms per 1 mol of molecules) m(5 mol C atoms) = 60.0 g 40% of xylose is carbon, so 40% of M(xylose) = 60.0 This can also be written as 0.40 × M(xylose) = 60.0 M(xylose) = = 150.0 gmol-1

60.00.40 (VCAA Q3 June 2008)



The amount of calcium carbonate (:molar mass = 100.1 g ) in the ore dolomite can be determined by gravimetric analysis. The dolomite sample is dissolved in acid and the calcium ions () present are precipitated as calcium oxalate ( :molar mass = 128.1 g ). The calcium oxalate is foltered, dried and strongly heated to form calcium oxide (CaO); molar mass = 56.1 g ). In one analysis the mass of dolomite used was 3.72 g. The mass of calcium oxide formed was found to be 1.24 g. The percentage of calcium carbonate in the dolomite sample is closest to

QUESTION 2

A. 26.9

B. 33.3

C. 56.0

D. 59.5 (VCAA Q8 June 2005)



The amount of calcium carbonate (:molar mass = 100.1 g ) in the ore dolomite can be determined by gravimetric analysis. The dolomite sample is dissolved in acid and the calcium ions () present are precipitated as calcium oxalate ( :molar mass = 128.1 g ). The calcium oxalate is foltered, dried and strongly heated to form calcium oxide (CaO); molar mass = 56.1 g ). In one analysis the mass of dolomite used was 3.72 g. The mass of calcium oxide formed was found to be 1.24 g. The percentage of calcium carbonate in the dolomite sample is closest to

QUESTION 2 (ANSWER)

A. 26.9

B. 33.3

C. 56.0

D. 59.5



(VCAA Q8 June 2005)

Alternative D is the correct answer n(CaO) = n(Ca2+) = n(CaO) = n(CaCO3) = 0.0221 m(CaCO3) in dolomite = 0.0221 × 100.1 = 2.21g %(CaCO3) =

2.21 100 59.5%3.72 1

× =

2.21 100 59.5%3.72 1

× =



When 2.54 g of solid iodine reacts with excess chlorine and the unreacted chlorine is evaporated, 4.67 g of a yellow product remains. The empirical formula of the product is

A. ICl2

B. ICl3

C. ICl4

D. ICl5

QUESTION 3

(VCAA Q4 June 2007)



When 2.54 g of solid iodine reacts with excess chlorine and the unreacted chlorine is evaporated, 4.67 g of a yellow product remains. The empirical formula of the product is

A. ICl2

B. ICl3

C. ICl4

D. ICl5

QUESTION 3 (ANSWER)

The empirical formula is ICl3 so the correct answer is B The yellow product is only made up of chlorine and iodine In 4.67g of the yellow product, 2.54g is iodine and (4.67-2.54) 2.13g is chlorine Empirical formula: I : Cl 2.54g : 2.13g 0.0200 : 0.0600

1 : 3

2.54 2.13 : 126.9 35.5 (VCAA Q4 June 2007)




Volumetric Analysis

Simple titrations


CHEMISTRY



Key(Knowledge(

•  volumetric(analysis(including(determination(of(excess(and(limiting(reagents((and(titration(

curves):(simple((and(back)(titrations,(acidPbase(

(and(redox(titrations)(

•  calculations(including(amount(of(solids,(liquids(and(gases;(concentration;(volume,(pressure(and(

temperature(of(gases(

•  the(application(of(chemical(equations(to(volumetric((and(gravimetric)(analyses(



Key(skills((a(reminder)(These(skills(include(the(ability(to:(

! conduct(investigations(that(include(collecting,(processing,(recording(and(analysing(qualitative(

and(quantitative(data;(draw(conclusions(

consistent(with(the(question(under(investigation(

and(the(information(collected;(evaluate(

procedures(and(reliability(of(data(

! construct(questions((and(hypotheses);(plan(and/or(design,(and(conduct(investigations;(identify(

and(address(possible(sources(of(uncertainty(



Volumetric(analysis(

•  A(technique(in(which(two(solutions(are(reacted(together.(

•  Typically(we(will(be(conducting(an(acidPbase(reaction,(or(a(redox(reaction.(

•  Concentration(of(one(solution(must(be(accurately(known((the(‘known’)(

•  We(use(a(Primary(standard(to(make(up(a(standard(solution(in(a(volumetric(or(standard(@lask.(



What(is(a(Primary(standard?(•  Solid(at(room(temp(•  Readily(obtainable(in(pure(form(•  Known(formula((Does(not(react(with(atmosphere)(

•  High(molar(mass(–(small(amount(has(a(reasonable(mass(

•  Cheap(•  eg(anhydrous(sodium(carbonate((Na2CO3)(potassium(hydrogen(phthalate(KH(C8H4O4)(

•  NOT(NaOH(and(HCl(



Standard(solution(

•  Made(up(in(standard((volumetric)(@lask(•  So(volume(is(known(accurately((•  Known(mass(of(solute(is(measured(and(transferred(into(the(@lask(

•  Solution(will(have(an(accurately(known(concentration(with(very(small(error(

•  Remember:(concentration(=(•  Volume(must(be(in(litres!((

amountvolume



Making(a(standard(solution(



Volumetric(Pipette(

•  Used(to(very(accurately(dispense(a(known(volume((aliquot)(of(the(standard(solution(

(accurately(known(concentration)(into(a(

conical(@lask.(

•  Uncertainty(is(usually(±0.05mL,(although(does(change(with(size(of(pipette(



Correct(use(of(pipette



BureDe&

•  Dispenses(a(volume((titre)(of(the(‘unknown’(solution((concentration(unknown)(into(the(aliquot(that(is(already(in(the(conical(@lask.(

•  Burette(is(graduated,(so(volume(is(determined(by(difference(between(initial(reading(and(@inal(reading(

•  Uncertainty(is(usually(±0.02(mL(per(reading,(so(will(be(±0.04(mL(for(one(volume(delivered.(



Correct(use(of(burette



Titration(

•  The(addition(of(a(solution(from(the(burette(into(a(conical(@lask(containing(an(aliquot(is(

called(a(titration.(

•  If(an(acidPbase(reaction(is(being(performed,(an(acidPbase(indicator(is(used(

to(determine(the(end(of(the(titration.(



The(end(of(a(titration((

•  The(equivalence(point(of(a(titration(is(the(point(at(which(the(exact((stoichiometric)(

amount(of(acid(has(been(added(to(react(

with(the(base(in(the(conical(@lask.(

•  In(a(titration,(we(aim(to(stop(adding(the(acid(from(the(burette(at(the(equivalence(

point.(This(is(called(the(end(point(and(is(

determined(by(the(indicator(changing(

colour.(



Indicators(

•  An(indicator(is(usually(a(weak(acid(which(is(a(different(colour(in(its(acidic(form(and(its(

basic(form.(

•  It(can(be(represented(as(HIn((acid(form)(HIn(aq)(⇌(H+(aq)(+(InP(aq)(

((((((((((Colour(1(((((((((((((((colour(2(



•  Considering(the(reaction:(Na2CO3(aq)((+(2HCl(aq)(→(2NaCl(aq)(+((H2O(l)(+(CO2(aq)(

aliquot ((((titre(

•  The(methyl(orange(indicator(is(yellow(in(the(sodium(carbonate(solution(because(it(was(in(its(basic(form((InP)(

InP(aq)((+((H+(aq)(→((HIn(aq)(methyl(orange:yellow ( ( (pink(

•  The(HCl(reacted(with(the(sodium(carbonate(until(none(was(left,(then(it(reacted(with(the(indicator(which(gained(an(H+(and(turned(into(HIn(

(

•  This(colour(change(is(the(endpoint(



Accuracy(•  The(accuracy(of(volumetric(analysis(is(obtained(by(repeating(the(titration(until(we(

obtain(3(concordant(results.((

•  Concordant(results(fall(within(a(range(of(0.10mL(ie(The(smallest(titre(is(no(more(than(

0.10mL(less(than(the(largest(titre.(

Non-concordant values



Acid(base(equations(which(MUST(be(

known(! Acid&+&base&→&salt&+&water&

((((((((((((((((((((eg(HCl(aq)(+(NaOH(aq)(→(NaCl(aq)((+(H2O(l)(

Ionic(equation:((H+((aq)(+(OHP((aq)(→((H2O(l)(

(

! Acid&+&carbonate&→&&&

& & &&&&&&&&salt&+&water&+&carbon&dioxide&

(((((((((((((((((eg((2HCl(aq)(+(Na2CO3(aq)(→(2NaCl(aq)(+(CO2(g)(+(H2O(l)(

Ionic(equation:(2H+((aq)(+(CO32P((aq)(→((CO2(g)(+(H2O(l)(

(

! Acid&+&hydrogencarbonate&&&& &&&&&&&&&&&&&&&→&&salt&+&water&+&carbon&dioxide&

(((((((((((((((((((eg((HCl(aq)(+(NaHCO3(aq)(→(NaCl(aq)(+(CO2(g)(+(H2O(l)(

Ionic(equation:(H+((aq)(+(HCO3P((aq)(→(CO2(g)(+(H2O(l)(

(



Using(titration(results(to(@ind(

concentration(of(unknown.(

1.  Average(the(concordant(titres.(This(gives(you(the(volume(of(solution(that(reacted(

with(the(aliquot.(

2.  Use(the(known(concentration(of(the(standard(solution(and(the(volume(of(the(

pipette((the(aliquot)(to(@ind(the(amount(of(

primary(standard(in(an(aliquot:(n(=(cV(



3.  Use(the(molar(ratio(from(the(equation(for(the(reaction(to(@ind(the(amount(in(mol(of(acid(that(

reacted(with(the(aliquot(of(standard(solution.(

4.  Find(concentration(of(acid(by(dividing(amount(that(reacted(by(average(volume(of(titre:((

( (c(=(( nV



Sample(exam(question(based(on(a(simple(

titration(

Titration(between(standard(solution(of(HCl(and(NaHCO3.(100.0(mL(of(1.00M(HCl(solution(was(to(be(diluted(to(0.100M(in(1.00L(volumetric(@lask,(but(900(mL(of(0.0222M(NaOH(was(added(instead(of(water.(

(a) Write(the(equation(for(the(reaction(that(occurs(in(the(volumetric(@lask.(

(b) Calculate(the(concentration(of(the(HCl(in(the(volumetric(@lask.(Correct(sig(@igs.(

(c)  If(contaminated(HCl(is(used(in(the(titration,(will(the(calculated(concentration(of(HCO3(be(greater(or(smaller(than(the(true(value.(Justify(your(answer(

(VCAA(June(2009(Question(3)(



(a)(In(the(volumetric(@lask:(

(((((((((HCl(aq)((+((NaOH(aq)((→ NaCl(aq) + H2O(l) (b) Calculate n(HCl) = cV = 1.00 × 0.100 = 0.100 mol n(NaOH)added = cV = 0.0222(×(0.900 = 0.01998 mol n(HCl)remaining after reaction = 0.100 – 0.01998 = 0.08002 mol Concentration = = 0.08002 M (c) The(concentration(of(HCl(is(lower(than(we(are(expecting,(((so(a(greater(volume(of(HCl(will(be(required(to(

react(with(the(NaHCO3.(This(will(make(it(seem(as(though(

the(NaHCO3(is(more(concentrated(than(it(actually(is,(so(the(

calculated(concentration(of(HCO3(will(be(greater(than(it(actually(is.(

(

nV




Volumetric Analysis

Titration Curves


CHEMISTRY



Key(Knowledge(

•  volumetric(analysis(including((determination(of(excess(and(limiting(

reagents(and)(titration(curves:(simple((and(

back)(titrations,(acidPbase((and(redox)(

titrations(



TitraFon&curves&

•  As(an(acid(is(added(to(a(basic(solution,((or(a(base(added(to(an(acidic(solution)(the(pH(of(

the(solution(changes.(

•  As(we(near(the(((((equivalence(point,((

(((the(pH(changes((

(((more(rapidly.(



•  A(titration(curve(tells(us((– whether(the(starting(solution(was(an(acid(or(a(base(AND(whether(it(was(

strong(or(weak((

– The(volume(of(the(second(solution(added(when(neutralisation(occurred(

– The(pH(at(the(equivalence(point(



Choice(of(indicator(

•  Each(different(indicator(has(a(particular(pH(range(in(which(it(changes(colour.(

•  Methyl(orange(changes(colour(from((((((pH(=(3.2(to(4.4.(

•  This(means(that(it(will(change(colour((have(an(endpoint)(near(the(equivalence(point(of(the(reaction(between(HCl(and(Na2CO3(–(a(strong(acid(and(a(weak(base.(



•  Phenolphthalein(changes(colour(in(the(pH(range(8.2(P(10.0(making(it(suitable(for(the(

titration(of(a(weak(acid(with(a(strong(base.(

•  See&data&booklet&table&11&



•  When(a(strong(acid(is(titrated(with(a(strong(base,(the(equivalence(point(is(at(pH(=(7.(

•  Phenolphthalein(can(be(used,(or(even(methyl(orange,(but(it(might(be(better(to(use(

another(indicator,(such(as(bromothymol(

blue(which(changes(colour(between(6.0(and(

7.6(((



Neutralising&strong&and&weak&acids&

•  Students(commonly(assume(that(a(strong(acid(will(require(more(base(to(neutralise(it(

than(a(weak(acid,(but(this(is(NOT(true.(

•  Consider(the(equations(for(the(reactions:(HCl(aq)((+((NaOH(aq)(→ NaCl(aq) + H2O(l) Strong acid CH3COOH(aq)((+((NaOH(aq)(→ weak acid CH3COONa(aq) + H2O(l) Both(demonstrate(a(1:1(ratio(with(NaOH(



Sample(exam(questions(–(pH(curves(

The(following(titration(curve(was(obtained(by(measuring(the(pH(in(a(reaction(@lask(during(an(acidPbase(titration(

The(graph(represents(the(change(

in(pH(in(the(reaction(@lask(when(

(

(

(

A.  A(weak(acid(is(added(to(a(strong(base(B.  A(weak(base(is(added(to(a(strong(acid(C.  A(strong(acid(is(added(t(a(weak(base(D.  A(strong(base(is(added(to(a(weak(acid.((

VCAA(June(2010(Q1(



Which(one(of(the(following(is(a(suitable(indicator(for(use(in(this(titration?(

A.  Phenol(red(B.  Thymol(blue(C.  Phenolphthalein(D.  Bromophenol(blue((

(

(

(

VCAA(June(2010(Q2(



Sample&exam&quesFon&–&FtraFng&strong&and&weak&acids&Two(titrations(were(performed(as(shown(below(

(

(

(

(

Which(one(of(the(following(statements(is(true?(

A.  The(weak(acid(will(require(a(greater(volume(of(NaOH(solution(than(the(strong(acid(to(reach(the(equivalence(point(

B.  The(weak(acid(will(require(a(smaller(volume(of(NaOH(solution(than(the(strong(acid(to(reach(the(equivalence(point(

C.  The(weak(acid(will(require(the(same(amount(of(NaOH(solution(as(the(strong(acid(to(reach(the(equivalence(point(

D.  The(equivalence(point(in(a(titration(of(a(weak(monoprotic(acid(with(NaOH(solution(cannot(be(determined.(

VCAA(June(2011(Q11(




Volumetric Analysis

Back Titrations

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/chemical-analysis-vol-analysis-back-titrations/key-knowledge /

CHEMISTRY



Key(Knowledge(

•  volumetric(analysis(including(determination(of(excess(and(limiting(reagents((and(titration(curves):((simple(and)(back(titrations,(acidPbase(and(redox(titrations(

•  calculations(including(amount(of(solids,(liquids(and(gases;(concentration;((volume,(pressure(and(temperature(of(gases)(

•  the(application(of(chemical(equations(to(volumetric((and(gravimetric)(analyses(



Back(titrations(

•  The(reaction(between(a(weak(acid(and(a(weak(base(does(not(give(a(sharp(change(in(pH(at(the(end(point,(so(there(is(not(a(distinct(colour(change.(

•  This(makes(it(impossible(to(perform(a(direct(titration.(

•  Instead(a(back(titration(is(used.(•  In(a(back(titration(two(reactions(occur,(one(after(the(other.(

•  Both(reactions(are(likely(to(be(acidPbase(reactions.(



1.  A(measured(excess(of(a(strong(base(is(added(to(the(weak(acid(to(make(sure(that(it(all(reacts.(

(Weak&acid&+&strong&base&→ salt + water &

2.  After(reaction,(the(remaining(strong(base(is(titrated(with(a(strong(acid.(In(this(way(the(amount(of(remaining(strong(base(can(be(accurately(determined.(

(Strong&acid&+&strong&base&→ salt + water &

3.  Knowledge(of(how(much(strong(base(was(originally(added(allows(the(calculation:(

(

n(reacting)&=&n(added&initially)&–&n(remaining)&



Amount&of&strong&base&

that&reacted&with&the&

weak&acid&

Amount&of&strong&base&that&

did&not&react&with&the&weak&

acid,&but&was&titrated&later&

with&the&strong&acid&

Total&

amount&

of&

strong&

base&

added&

initially&

The(distribution(of(added(strong(base(in(a(back(titration(



Calculations(associated(with(back(

titrations(

•  (1)(Total(amount(of(strong(base(added(initially(=(volume(×(concentration(

•  (2)(Amount(of(strong(base(that(did&not&react(with(the(weak(acid(is(found(

in(the(titration.(

! n(strong(acid)(=(cV(titre)(! n(strong(base)(=(n(strong(acid)((for(a(monoprotic(acid(–(most(common)(

&



•  Amount(of(strong(base(that(did&react&with(the(weak(acid(is(found(by(subtraction:(

n(reacting)&=&n(added&initially)&–&n(remaining)&

•  Amount(of(weak(acid(in(the(original(sample(is(then(found(from(the(equation(for(the(reaction(between(

the(reacting(strong(base(and(the(original(weak(

acid.(

&



Sample(exam(question(–(back(

titration(0.415(g(of(a(pure(acid,(H2X(s)(is(added(to(exactly(100(mL(of(0.105(M(NaOH(aq).(A(reaction(occurs(according(to:(

H2X(s)((+((2NaOH(aq)((→ Na2X(aq) + 2H2O(l) The NaOH is in excess. This excess NaOH requires 25.21 mL of 0.197M HCl(aq) for neutralisation. (a)  Calculate the amount, in mol, of NaOH that is added to

the acid H2X initially. (b) Calculate the amount, in mol, of NaOH that reacts with

the acid H2X. (c)  Calculate the molar mass, in gmol-1, of the acid H2X.

VCAA June 2008 Q8(



Answer((a)  n(NaOH)(=(cV(=(0.105(×(0.100(=(0.0105&mol&&

b)  NaOH(+(HCl(→(NaCl(+(H2O(((((((((EXCESS(NaOH(was(titrated(with(HCl,(so(

n(NaOH)excess(=(n(HCl)(=(0.197(×(0.02521(=(0.004966(mol(

n(NaOH)reacting(with(H2X(=(0.0105(P(0.004966(=(0.00553&mol&

&

c)  (H2X(s)((+((2NaOH(aq)((→ Na2X(aq) + 2H2O(l) ((((((so(n(H2X)(=(½(n(NaOH)(=(0.002767(mol(

((((((0.002767(mol(H2X(has(a(mass(of(0.415g(

((((((so(1(mol(of(H2X(has(a(mass(of( ( ((((=(150(g(molP1(

(

0.4150.002767



1. The graph below shows the change in pH of a reaction solution during a titration of 0.10M NaOH with 0.10M CH3COOH A suitable indicator for the titration and the colour change observed is

QUESTION 1

Indicator Colour change

A. Methyl red Yellow to red

B. Methyl red Red to yellow

C. Phenolphthalein Colourless to red

D. Phenolphthalein Red to colourless (VCAA Q4 June 2008)



1. The graph below shows the change in pH of a reaction solution during a titration of 0.10M NaOH with 0.10M CH3COOH A suitable indicator for the titration and the colour change observed is

QUESTION 1 (ANSWER)

Indicator Colour change

A. Methyl red Yellow to red

B. Methyl red Red to yellow

C. Phenolphthalein Colourless to red

D. Phenolphthalein Red to colourless



Phenolphthalein suits this titration best because the equivalence point is at approximately pH = 9. Phenolphthalein changes colour (according to the data book) between pH = 8.3 and 10.0, so would suit this equivalence point. The titration starts at a high pH, when phenolphthalein is red and then it would become colourless.

(VCAA Q4 June 2008)



2. 20.0 mL of 0.10 M hydrochloric acid (HCl) reacts with 20.0 mL of 0.30 M potassium hydroxide (KOH) solution. The concentration of potassium ions in the resultant solution, in mole per litre, is

QUESTION 2

A. 0.10 B. 0.15 C. 0.20 D. 0.30

(VCAA June 2005 Q 13)



2. 20.0 mL of 0.10 M hydrochloric acid (HCl) reacts with 20.0 mL of 0.30 M potassium hydroxide (KOH) solution. The concentration of potassium ions in the resultant solution, in mole per litre, is

QUESTION 2 (ANSWER)

A. 0.10 B. 0.15 C. 0.20 D. 0.30




n(KOH) = 0.30 × 0.0200 = 0.0060 mol total volume of solution = 40.0 mL = 0.0400 L c(K+) ions = Note that the fact that the HCl reacts with the KOH has nothing to do with the final concentration of K+ ions.

-10.00600.15 molL

0.04=




3. Sulfuric acid (H2SO4) and nitric acid (HNO3) are both strong acids. Ethanoic acid (CH3COOH) is a weak acid. 20.00 mL solutions of 0.10 M concentration of each of these three acids were separately titrated with a 0.10 M solution of sodium hydroxide (NaOH). In order to react completely

QUESTION 3

A. All three acids would require the same amount of NaOH

B. HNO3 would require more NaOH than CH3COOH but less than H2SO4.

C. H2SO4 and HNO3 would require the same amount of NaOH but CH3COOH would require less.

D. CH3COOH and HNO3 would require the same amount of NaOH but H2SO4 would require more.

(VCAA June 2006 Section A Q5)



3. Sulfuric acid (H2SO4) and nitric acid (HNO3) are both strong acids. Ethanoic acid (CH3COOH) is a weak acid. 20.00 mL solutions of 0.10 M concentration of each of these three acids were separately titrated with a 0.10 M solution of sodium hydroxide (NaOH). In order to react completely

QUESTION 3 (ANSWER)

A. All three acids would require the same amount of NaOH

B. HNO3 would require more NaOH than CH3COOH but less than H2SO4.

C. H2SO4 and HNO3 would require the same amount of NaOH but CH3COOH would require less.

D. CH3COOH and HNO3 would require the same amount of NaOH but H2SO4 would require more.



H2SO4 is a diprotic acid, so it is not the strength of the acid, but its proticity that matters here. For every one mol of H2SO4 reacting, two mol of NaOH would be required, while for every one mol of CH3COOH or HNO3 reacting, only one mol of NaOH would be required.

Note that the fact that CH3COOH is a weak acid does not have any bearing on the acid. Equal mol of strong or weak acids react with equal mol of NaOH.

(VCAA June 2006 Section A Q5)



4.(a) The hydrogen carbonate ion, (HCO3-) can act both as an acid and as a

base.

QUESTION 4(a)

Please write down your answer on a piece of paper. We will show you the answer in the next section.

i. Write a chemical equation that shows HCO3- acting as an acid when it reacts with water.

ii. Write a chemical equation that shows HCO3

- acting as an base when it reacts with water.

(2 marks)

(VCAA June 2006 Q5 Parts [a] and [c][i])



4.(a) The hydrogen carbonate ion, (HCO3-) can act both as an acid and as a

base.

QUESTION 4(a) (ANSWER)

i. Write a chemical equation that shows HCO3- acting as an acid when it reacts with water.

HCO3-(aq) + H2O(l) � CO3

2-(aq) + H3O+(aq) Note that when HCO3

- is acting as an acid, it will donate an H+ to the water. ii. Write a chemical equation that shows HCO3

- acting as an base when it reacts with water. HCO3

-(aq) + H2O(l) � H2CO3(aq) + OH-(aq) Note that when HCO3

- is acting as an base, it will accept an H+ from the water. (2 marks)




4(b). The hydrogen ion concentration of a solution is described by the term pH. The hydroxide ion concentration is described in the same way by the term pOH. A solution has a pOH of 3 at 25°C.

QUESTION 4(b)

M

i. Calculate the hydroxide ion concentration of the solution in mol L-1




4(b). The hydrogen ion concentration of a solution is described by the term pH. The hydroxide ion concentration is described in the same way by the term pOH. A solution has a pOH of 3 at 25°C.

QUESTION 4(b) (ANSWER)

i. Calculate the hydroxide ion concentration of the solution in mol L-1


Answer : 0.001 M If pOH is described in the same way as pH (pH = -log[H3O+]), then pOH = -log[OH-] So [OH-] = 10-pOH = 10-3 = 0.001 M


We do our best to make these slides comprehensive and up-to-date, however there may be errors. We'd appreciate it if you pointed these out to us! 79 79

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Volumetric Analysis

Oxidation Numbers and Partial Ionic Equations

CHEMISTRY



Key(Knowledge(

•  volumetric(analysis(including(determination(of(excess(and(limiting(reagents((and(titration(

curves):((simple(and(back(titrations,(acidPbase)(

and(redox(titrations(

•  calculations(including(amount(of(solids,(liquids(and(gases;(concentration;((

•  the(writing(of(balanced(chemical(equations,(including(the(use(of(oxidation(numbers(to(write(

redox(equations,(and(the(application(of(chemical(

equations(to(volumetric((and(gravimetric(

analyses)(

80



Redox(reactions(

•  A(redox(reaction(involves(the(transfer(of(electrons(from(a(reductant(to(an(oxidant.(

•  Reductants(are(usually(metals(eg(Mg,(Zn(or(nonPmetal(anions(eg(ClP,(BrP(

•  Oxidants(are(usually(nonPmetals(eg(Cl2,(O2(or(metal(cations(eg(Cu2+,(Ag+(

•  A(redox(reaction(usually(results(in(the(formation(of(an(ionic(compound.(

81



•  Oxidation(is(the(loss(of(electrons(•  An(oxidation(half(equation(has(electrons(on(the(right(

•  Reductants(undergo(oxidation(Mg(→(Mg2+(+(2eP(

(

•  Reduction(is(the(gain(of(electrons(•  A(reduction(half(equation(has(electrons(on(the(left(

•  Oxidants(undergo(reduction(O2(+((4e

P((→(2O2P(

82



Overall(equations(

•  An(oxidation(reaction(cannot(occur(without(a(reduction(reaction(

•  When(two(half(equations(are(combined(the(electrons(must(be(balanced(on(both(sides(of(

the(equation(–(no(left(over(electrons.(

83



Oxidation(numbers(

•  Oxidation(numbers(are(used(to(judge(whether(a(substance(is(undergoing(reduction(or(oxidation.(

•  Follow(the(rules(to(assign(oxidation(numbers((

•  While(oxidation(numbers(are(‘manPmade’(they(represent(the(charge(that(would(appear(if(the(element(were(to(completely(lose((or(gain)(electrons,(rather(than(just(sharing(in(a(covalent(bond.(

84



! An(increase(in(oxidation(number(during(a(chemical(reaction(indicates(that(the(substance(has(been(oxidized.(

! A(decrease(in(oxidation(number(indicates(that(the(substance(has(been(reduced.(

! eg((Fe(s)((+((Cu2+(aq)((→(Fe2+(aq)((+((Cu(s)(

ONs(((0((((((((((((+2(((((((((((((((((((+2((((((((((((((((0(

(

Fe(has(increased(from(0(to(+2((has(been(oxidised)(

Cu(has(decreased(from(+2(to(0((has(been(reduced)(

86



Sample(exam(question(–(oxidation(

numbers(The(equation(for(a(reaction(that(occurs(during(the(extraction(of(iron(from(iron(ore(is(

Fe2O3(s)((+((3CO(g)((→((2Fe(l)((+((3CO2(g)(

(

During(this(reaction(the(oxidation(number(of(iron(changes(

from(

A.  +(3(to(0,(and(CO(is(the(reductant(B.  +6(to(0,(and(CO(is(the(reductant(C.  +3(to(0(and(CO(is(the(oxidant(D.  +6(to(0(and(CO(is(the(oxidant(

VCAA(June(2006(Q14(

87



Balancing(partial(ionic(equations(

•  Some(half(equations(are(not(as(simple(as(((((Fe2+((+((2eP((→((Fe(

•  They(may(involve(oxygen(atoms,(such(as(when(H2SO4(is(reduced(to(form(H2S(

•  In(this(case(a(special(method(is(used(to(balance(the(equation(

88



Step& Example&ReducFon&of&Cr2O7

2B&to&Cr3+(

Balance&all&atoms&except&O&and&H(

Cr2O72B&&&&&&&→&&&Cr3+&

(

Balance&O&atoms&using&&H2O(

Cr2O72B&&&&&&&→&&&Cr3+&

(

Balance&H&atoms&using&&H+(

Cr2O72B&&&&&&&&&&&&&→&&&Cr3+&

(

Balance&charge&using&electrons(

Cr2O72B&&&&&&&&&&&&&&&&&&&&→&&&Cr3+&

(

Add&state&symbols(

89



Sample(exam(question(–(balancing(

partial(ionic(equations&When(this(half(equation(is(balanced(

correctly,((

VO2+(aq)(+(xH2O(l)(→(VO3P(aq)(+(yH+(aq)(+(zeP(

the(coef@icients,(x,(y(and(z(are(equal(to(A.  1,(2,(4(B.  2,(4,(1(C.  2,(4,(2(D.  3,(6,(2(&



VO2+(aq)(+(_H2O(l)(→(VO3P(aq)(+(_H+(aq)(+(_eP((

•  Balance(oxygen(using(H2O(•  Balance(hydrogen(using(H+(

•  Balance(charge(using(eP(

•  The(answer(is(B(



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Volumetric Analysis

Redox Titrations

CHEMISTRY



How(does(a(redox(titration(differ(to(an(

acidPbase(titration?(

•  Often(an(indicator(is(not(required(because(the(reactant(and(product(have(different(

colours(

•  eg(Cr2O72P(is(orange(while(Cr3+(is(green(•  In(other(redox(titrations(an(�indicator�(such(as(starch(solution(is(added(near(the(

end(point.(It(will(react(with(the(excess(

titrant.(



What(sort(of(reactants(can(be(analysed(

using(a(redox(titration?(

•  Sulfur(dioxide(P(a(preservative(used(in(wine:(titrate(with(iodine(solution(

•  Ethanol(–(major(component(of(wine:(titrate(with(thiosulfate(solution(after(reaction(with(

excess(dichromate(

•  Vitamin(C(–(in(fruit(juices:(titrate(with(iodine(solution(



Sample(exam(question(–(redox(titrations(

The(amount(of(iron(in(an(aluminium(alloy(is(to(be(determined.(80.50(g(of(alloy(is(dissolved(in(HCl(and(iron(

atoms(convert(to(Fe2+((aq)(ions.(This(solution(is(transferred(

to(a(250.0(mL(volumetric(@lask(and(made(up(to(mark.(20.00(

mL(aliquots(of(this(solution(are(titrated(against(0.0400(M(

KMnO4(solution.(

5Fe2+(aq)(+(MnO4P(aq)(+(8H+(aq)(→(5Fe3+(aq)(+(Mn2+(aq)(+(4H2O(l)(

Four(titrations(were(carried(out:(

(

(

VCAA((June(2010(Q1(

Titra:on'number' 1' 2' 3' 4'Vol&of&KMnO4&(mL)& 22.03& 20.25& 21.97& 21.99&



(a)(Write(a(balanced(halfPequation,(including(states,(for(the(conversion(of(MnO4

P(in(an(acidic(solution(to(Mn2+(ions.(

Answer:((MnO4P((((((((((((((((((((((((((((((((((((((Mn2+(

(

(b)(Calculate(the(average(volume,(in(mL,(of(the(concordant(

titres(of(the(KMnO4(solution(

Answer:(20.25(mL(is(not(concordent,(so(do(not(include(in(

average(

Average(=((22.03(+(21.97(+(21.99)/3(=(22.00(mL(

(c)((Use(your(answer(to(part((b)(to(calculate(the(amount,(in(

mol,(of(MnO4P((aq)(ions(used(in(this(titration.(

Answer:(n(=(cV(=(0.0400(×(0.02200(=(8.80(×(10P4(mol(

(

(

(

(



(d)((Calculate(the(amount,(in(mol,(of(Fe2+(ions(present(in(the(250.0(mL(volumetric(@lask(

Answer:(n(Fe2+)(in(20.00(mL(=(5(×(n(MnO4P)(=(5(×(8.80(×(

10P4(=(4.40×(10P3(mol(

n(Fe2+)(in(250.00(mL(=(4.40×(10P3(×( (=(0.0550(mol(

(

(e)((Calculate(the(percentage(by(mass,(of(iron(in(the(80.50(g(

sample(of(alloy.(Express(your(answer(to(the(correct(

number(of(signi@icant(@igures.(

Answer:(m(Fe)(=(n(Fe2+)(×(55.8(=(0.0550(×(55.8(=(3.069g(

%Fe(=( ((((((((((=(3.81%(

(

(Note(that(the(current(data(book(gives(Ar(Fe)(to(be(55.8,(

whereas(in(2010(it(was(given(as(55.9)(

250.020.00

3.069 10080.50 1

×



QUESTION 1&

Which one of the following is least likely to be a product of a redox reaction between sulphuric acid and zinc metal?

A. H2

B. H2S

C. SO2

D. SO3

(VCAA Q9 June 2007)



QUESTION 1&

Which one of the following is least likely to be a product of a redox reaction between sulphuric acid and zinc metal?

A. H2

B. H2S

C. SO2

D. SO3



The correct answer is D Before you do anything, consider the oxidation number of S in sulfuric acid and of Zn: S in H2SO4 – oxidation number is +6 – this is the highest oxidation number that S can have (is equivalent to the S atom losing all 6 electrons in its valence shell). Since the oxidation number must change in a redox reaction, this means that the oxidation number of S must be less than +6 in the products. (reduction) Oxidation number of Zn is 0. Its oxidation number must increase in the reaction (oxidation). Also a standard reaction that should be known is �acid + reactive metal � salt + hydrogen gas� We are looking for the least likely answer: A. is quite likely (see standard reaction above) B. oxidation number of S is -2. This is possible (S has been reduced) C. oxidation number of S is + 4. This is also possible D. oxidation number of S is +6. The S has not been reduced, therefore this cannot be the result of a redox reaction.

(VCAA Q9 June 2007)



QUESTION 2&

When solid sodium hydride, NaH, is added to water, the hydride ion reacts according to the following equation. H-(aq) + H2O(l) � OH-(aq) + H2(g) This reaction can be classified as

A. Acid-base only

B. Oxidation-reduction only

C. Both acid-base and oxidation-reduction

D. Neither acid-base nor oxidation-reduction

(VCAA Q7 June 2009)



QUESTION 2 (ANSWER)&

When solid sodium hydride, NaH, is added to water, the hydride ion reacts according to the following equation. H-(aq) + H2O(l) � OH-(aq) + H2(g) This reaction can be classified as

A. Acid-base only

B. Oxidation-reduction only

C. Both acid-base and oxidation-reduction

D. Neither acid-base nor oxidation-reduction



The correct answer is C. With any question of this sort, the first thing you do is check oxidation numbers. If they change, then you have a redox reaction. After that you can look for transfer of H+ ions. Oxidation numbers: -1 +1 -2 -2 +1 0 H-(aq) + H2O(l) � OH-(aq) + H2(g) The oxidation number of O has not changed, but that of H has changed from -1 to 0 (oxidation) and from +1 to 0 (reduction), so this is a redox reaction. Also, an H+ ion has been transferred from H2O to H- forming the OH- (conjugate base of H2O) and H2 (conjugate acid of H-), so this is also an acid-base reaction.

(VCAA Q7 June 2009)



In the following four substances, H2S2O7, N2O5, HIO3, Cl2O7, the atom with the highest oxidation number is

QUESTION 3&

(VCAA Q18 June 2005)

A. I

B. S

C. N

D. Cl



In the following four substances, H2S2O7, N2O5, HIO3, Cl2O7, the atom with the highest oxidation number is

QUESTION 3 (ANSWER)&


A. I

B. S

C. N

D. Cl

The correct answer is D Calculate the oxidation number of each of the four atoms in the four molecules H2S2O7 oxidation number of S: (2 × +1) + 2x + (7×-2) = 0, 2x = +12, x = +6 N2O5 oxidaton number of N: 2x + (5×-2) = 0, 2x = +10, x = +5 HIO3 oxidation number of I: +1 + x + (3 × -2) = 0, x = +5 Cl2O7 oxidation number of Cl: 2x + (7 × -2) = 0, x = +7



For quality control, a chemist analyses the vitamin C (molecular formula C6H8O6) content of a new brand of fruit juice. The reaction used is an oxidation-reduction reaction in which I3

- is the oxidant and vitamin C is the reductant. The reaction is C6H8O6(aq) + I3

-(aq) � C6H6O6(aq) + 2H+(aq) + 3I-(aq) The half equation for the reduction of I3

- to I- is I3-(aq) + 2e- � 3I-(aq)

QUESTION 4(a)

(VCAA Q2 June 2005)

(1 mark) (a) Give the half reaction for the oxidation of vitamin C.



For quality control, a chemist analyses the vitamin C (molecular formula C6H8O6) content of a new brand of fruit juice. The reaction used is an oxidation-reduction reaction in which I3

- is the oxidant and vitamin C is the reductant. The reaction is C6H8O6(aq) + I3

-(aq) � C6H6O6(aq) + 2H+(aq) + 3I-(aq) The half equation for the reduction of I3

- to I- is I3-(aq) + 2e- � 3I-(aq)

QUESTION 4(a)

(VCAA Q2 June 2005)

(1 mark) (a) Give the half reaction for the oxidation of vitamin C.

We have two equations to work with The overall equation: C6H8O6(aq) + I3

-(aq) � C6H6O6(aq) + 2H+(aq) + 3I-(aq) The reduction equation: I3

-(aq) + 2e- � 3I-(aq) The oxidation equation is found by subtraction of the reduction equation from the overall equation: C6H8O6(aq) � C6H6O6(aq) + 2H+(aq) + 2e- Quick check – this is an oxidation equation because the electrons are on the RHS (lost)



A 20.00 mL sample of the fruit juice was made up to 250.0 mL with pure water in a volumetric flask. 25.00 mL aliquots of the diluted fruit juice were then placed in a conical flask and titrated with a solution in which [I3

-] = 2.00 × 10-4 M. An average titre of 15.65 mL was obtained.

QUESTION 4(b)i

(VCAA Q2 June 2005)

(1 mark)

Note: Please follow this specific format while entering your answer: For example, if your answer is 10.5 x 10-10, enter it as 10.50*10^(-10) Please do not leave any spaces. Enter ^ by holding [shift] and pressing the 6 at the top of your keyboard.

(i) Calculate the amount of I3- present in the average titre, in mole.



QUESTION 4(b)i (ANSWER)

n(I3-) = cV (concentration of solution × volume of average titre)

= 2.00 × 10-4 × 0.01565 = 3.13 × 10-6 mol in the average titre



(VCAA Q2 June 2005)

(1 mark) (i) Calculate the amount of I3- present in the average titre, in mole.





QUESTION 4(b)ii

(VCAA Q2 June 2005)

(1 mark) (ii) Calculate the amount, in mole, of vitamin C present in each 25.00 mL aliquot.





QUESTION 4(b)ii (ANSWER)

(VCAA Q2 June 2005)

(1 mark) (ii) Calculate the amount, in mole, of vitamin C present in each 25.00 mL aliquot.

25.00 mL aliquots were titrated, so n(vitamin C) in 25.00 mL aliquot can be calculated using the equation for the reaction and the amount of I3

- in the average titre. Molar ratio C6H8O6(aq) : I3

-(aq) 1 : 1 n(C6H8O6)in 25.00 mL = n(I3

-) = 3.13 × 10-6 mol





QUESTION 4(b)iii

(VCAA Q2 June 2005)

(2 marks)

(iii) Calculate the concentration of vitamin C in the original (undiluted) sample of fruit juice in mole per litre.





QUESTION 4(b)iii (ANSWER)

(VCAA Q2 June 2005)

(2 marks)

(iii) Calculate the concentration of vitamin C in the original (undiluted) sample of fruit juice in mole per litre.

n(C6H8O6)in 250.0 mL = × 3.13 × 10-6 = 3.13 × 10-5 This is the same amount of vitamin C in the original 20.00 mL of orange juice, So, c(vitamin C) = in the original sample of fruit juice.



During the analysis the chemist rinsed, but did not dry, each item of glassware. She had available for use: pure water, the original fruit juice, the diluted fruit juice and the standard I3

- solution. For each item listed below, name the liquid that should be used to rinse it by placing a tick in the appropriate box.

QUESTION 4(c)

(VCAA Q2 June 2005)

(4 marks)

Pure Water Original Fruit Juice

Diluted Fruit Juice

Standard I3- Solution

20.00 mL pipette

250.00mL Volumetric Flask

25.00mL pipette

Conical Flask



During the analysis the chemist rinsed, but did not dry, each item of glassware. She had available for use: pure water, the original fruit juice, the diluted fruit juice and the standard I3

- solution. For each item listed below, name the liquid that should be used to rinse it by placing a tick in the appropriate box.

QUESTION 4(c) (ANSWER)

(VCAA Q2 June 2005)

(4 marks)

Pure Water Original Fruit Juice

Diluted Fruit Juice

Standard I3- Solution

20.00 mL pipette

✓

250.00mL Volumetric Flask

✓

25.00mL pipette

✓

Conical Flask ✓



QUESTION 5 (i)

(VCAA Q2 June 2008)

(1 mark)

One method of analysing the manganese content of steel is to dissolve the steel in nitric acid; producing a solution of manganese(II), Mn2+(aq). The Mn2+(aq) ions are then treated with an excess of acidified solution of periodate ions, IO4

-(aq). The products of this reaction are iodate ions, IO3

-(aq), and the deeply purple-coloured permanganate ions, MnO4

-(aq).

(i) Calculate the oxidation number of iodine in the IO4-(aq) ion.



QUESTION 5 (i) (ANSWER)

(VCAA Q2 June 2008)

(1 mark)




-(aq).

(i) Calculate the oxidation number of iodine in the IO4-(aq) ion.

Oxidation number of I in IO4-(aq): x + (4 × -2) = -1, x = +7



QUESTION 5 (ii)

(VCAA Q2 June 2008)

(1 mark)




-(aq).

(ii) Give a half equation for the conversion of IO4-(aq) into IO3

-(aq) in acid solution.

Note: please follow this specific format while entering your answer: Please do not leave any spaces. If your answer is AAB+(I) + CCD-(aq) + 3-> EEF+(I) + GGH-(aq) Please enter AAB(+)(I)+CCD(-)(aq)+3->EEF(+)(I)+GGH(-)(aq) To make the arrow enter a hyphen (next to 0, at the top of the keyboard) and then a greater than sign ([shift]+the second key right from M)



QUESTION 5 (ii) (ANSWER)

(VCAA Q2 June 2008)

(1 mark)




-(aq).

(ii) Give a half equation for the conversion of IO4-(aq) into IO3

-(aq) in acid solution.

IO4-(aq) + 2H+(aq) + 2e- � IO3

-(aq) + H2O(l) Balance Oxygens on LHS with water on RHS, Balance Hydrogens on RHS with H+ on LHS, Balance charge (+1 on LHS and -1 on RHS) with electrons



QUESTION 5 (iii)

(VCAA Q2 June 2008)

(1 mark)




-(aq).

(iii) Is the IO4-(aq) ion acting as an oxidant or reductant? Explain your choice.

Note: please only enter oxidant or reductant. We recommend you write your explanation down on some paper or in a document before you check your answer.



QUESTION 5 (iii) (ANSWER)

(VCAA Q2 June 2008)

(1 mark)




-(aq).

(iii) Is the IO4-(aq) ion acting as an oxidant or reductant? Explain your choice.

IO4- is reduced in the above half equation (it gains electrons), so it is the oxidant. This is

because it causes the other reactant to be oxidised and the IO4- is reduced.



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Chromatography

General Features and TLC

CHEMISTRY



Key(Knowledge:(

Principles(and(applications(of(chromatographic(

techniques((excluding(features(of(instrumentation(

and(operation),(and(interpretation(of(qualitative(and(

quantitative(data(from:(

•  (thin(layer(chromatography((TLC),(including(calculation(of(Rf(

•  high(performance(liquid(chromatography((HPLC)(•  gas(chromatography((GC)(including(Rt(and(the(use(of(a(calibration(graph(to(determine(amount(of(

analyte.(



General(features(of(chromatography(

•  A(technique(which(is(used(to(separate(parts(of(a(mixture.(

•  There(are(always(two(phases(–(the(stationary(phase(and(the(mobile(phase.(

•  Stationary(phase(does(not(move.(–(is(usually(a(solid,(but(may(be(a(viscous(liquid(coated(on(beads.((

•  Mobile(phase(is(a(liquid(or(gas(which(moves(over(the(stationary(phase(



Why(does(separation(occur?(

•  Components(have(different(structures,(so(are(capable(of(different(degrees(of(

intermolecular(bonding(

•  Separation(occurs(due(to(the(difference(in(solubility(in(the(mobile(phase(and(

difference(of(adsorption(to(stationary(

phase(of(the(components(of(the(mixture(



How(does(it(work?(

•  Sample(is(placed(at(the(origin((on(the(stationary(phase)(

(

•  The(mobile(phase(is(added(and(the(sample(starts(to(

move(along(the(stationary(

phase(as(the(mobile(phase(

moves((



•  The(different(components(separate(as(they(adsorb(onto(the(stationary(phase(

and(desorb(back(into(the(mobile(phase.(



Thin(layer(chromatography((TLC)(

•  Stationary(phase(–(glass(or(plastic(plate(with(thin(layer(of(aluminium(

oxide(powder(on(the(plate(

•  Mobile(phase(–(a(solvent(that(will(dissolve(the(sample.((

eg(water,(NaCl(aq)(or(a(mixture(of(two(or(

more(liquids(eg(methylated(spirits(and(

acetone.(



Interpreting(chromatograms(

•  A(chromatogram(is(the(pattern(of(bands(or(spots(formed(on(the(plate.(

•  Each(component(of(the(mixture(travels(a(different(distance(along(the(plate(or(paper.(

•  When(the(chromatogram(is(dried/developed(a(spot(or(line(is(present(to(

represent(the(component.((



Rf(values((Rf(=(retention(factor)(

•  Two(distances(are(measured(from(the(origin:(

– The(distance(that(the(solvent(has(travelled(The(distance(that(the(component(has(

travelled(



Qualitative(use(of(Rf(values(

•  The(Rf(value(is(used(to(identify(a(

component(by(

comparing(it(to(Rf((

(((values(of(known((

(((substances(under((

((the(same(conditions.(



TLC(Sample(exam(question(

1.  Consider(the(following(TLC(plate(of(compounds,(X,(Y(and(Z(developed(using(a(suitable(mobile(phase(on(

a(polar(stationary(phase(

(((((((The(Rf(value(of(the(most(polar(component(in(this((((

(((((((TLC(separation(is(

A.(0.29 (B.(0.62( (C.(0.78( (D.(0.80(


(



Answer(

A.((

•  The(most(polar(component(will(have(the(strongest(attraction(to(the(stationary(phase,(so(will(have(the(

smallest(Rf(value.((

•  Spot(X(has(travelled(the(smallest(distance(and(its(Rf(value(is(0.80/2.75(=(0.29(



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Chromatography

HPLC and GLC

CHEMISTRY



Column(chromatography(

(The(basis(for(HPLC(and(GLC)(

•  In(the(simplest(form,(column(((chromatography(is(carried((

(out(in(the(laboratory(

(in(a(glass(column(packed((

(with(a(solid(such(as((

(alumina,(Al2O3.(



HPLC(

•  Separation(occurss(in(a(short(column(

•  Stationary(phase:((very(@ine(solid((

(particles(tightly(

packed(eg(silica((

•  Mobile(phase:(liquid(under(high(pressure(to(force(its(way(through(the(solid(

&



The&Chromatogram&

137

Injection

Rt mAU

time

Rt

Rt - retention time - determines sample identity

Area or height is proportional to the quantity of analyte.



HPLC(Applications((

138

Chemical

Environmental

Pharmaceuticals

Consumer Products

Clinical

polystyrenes dyes phthalates

tetracyclines corticosteroids antidepressants barbiturates

amino acids vitamins homocysteine

Bioscience proteins peptides nucleotides

lipids antioxidants sugars

polyaromatic hydrocarbons Inorganic ions herbicides

•  HPLC(is(very(sensitive!(



HPLC(Sample(exam(question(

HPLC(uses(a(nonPpolar(stationary(phase(together(with(a(polar(mobile(phase.(Which(of(the(following(molecules(will(have(the(greatest(retention(time(on(such(a(column?(

( ( ( ((VCAA(June(2009(Q(5)(



Answer((

The(answer(is(A(

• Molecules(B,(C(and(D(are(all(polar.(To(see(this(observe(the(–OH(and(–NH(groups(on(the(

hydrocarbon(chain(of(the(molecules.(

• A(nonPpolar(molecule(will(have(the(greatest(attraction(to(the(stationary(phase,(so(will(take(the(

longest(time(to(move(along(the(column(=(greatest(

retention(time.(



GC(

•  Sample(and(the(solvent(it(is(dissolved(in(must(be(volatile(as(they(are(heated(in(an(

oven(

•  Mobile(phase:((((Inert(gas(

•  Stationary(phase:(((((porous(beads((

((((coated(with((

((((high(bpt(liquid(



•  Most(sensitive(of(all(chromatography(techniques(

•  Used(for(testing(urine(samples(for(drugs(•  Compounds(must(be(able(to(be(vaporised(without(decomposing((usually(low(

molecular(mass(<500(g(molP1(samples)(



SeparaFon&of&mixture&

•  Sample(passes(along(column(with(mobile(phase(

•  Passes(in(and(out(of(solution(in(stationary(phase(

•  Component(which(is(least(soluble(in(stationary(phase(will(be(eluted(@irst((moves(quickest(along(column)(

•  As(components(are(eluted(they(are(detected(by(@lame(ionisation(detector.(



Chromatogram(

•  A(graph(with(peaks(which(correspond(to(components(of(mixture(

•  Retention(time(=(time(taken(for(component(to(pass(through(column(



Quantitative(use(of(GC(

•  Run(a(series(of(standards(of(known(concentration(under(the(same(

conditions(as(the(sample.(

•  The(area(under(the(peak(is(proportional(to(the(amount(of(the(substance(present.(

•  Draw(a(calibration(graph(to(link(area(under(peak(to(concentration(

•  Find(sample(concentration(using(graph.(

145



GC(Sample(exam(questions(&

1. Analysis(of(the(components(of(a(mixture(using(gasPliquid(chromatography(normally(involves(measuring(

the(

(((((A.((Rf(values(of(components(using(a(gas(as(the(mobile((

phase(

(((((B.(Rf(values(of(components(using(a(liquid(as(the(mobile(

phase(

(((((C.((Retention(times(of(components,(using(a(gas(as(the(

mobile(phase.(

(((((D.(Retention(times(of(components,(using(a(liquid(as(the(

mobile(phase.(

( ( ( ((VCAA(June(2007(Q71)(

(

(

147



2.  This(diagram(shows(the(gas(chromatogram(of(a(sample(containing(4(straight(chain(alkanes.(Which(of(the(statements(that(follow(are(true?(

I.  The(boiling(points(of(the(compounds(arranged(from(highest(to(lowest(are(Z>Y>X>W(

II.  The(retention(times(will(stay(the(same(if(the(temperature(at(which(the(chromatogram(is(recorded(is(increased(and(all(other(conditions(remain(constant.(

III.  Hydrogen(gas(could(have(been(used(as(a(carrier(gas(to(obtain(this(chromatogram.(((((((((((((((((VCAA(June(2009(Q6)(

148



Answers(

1.  C(is(the(answer(Rf(values(are(used(for(TLC(and(paper(

chromatography,(while(retention(times(are(used(for(

columnPbased(chromatography.(In(GC,(the(mobile(

phase(is(a(gas.(

2.  Statements(I(and(III(are(correct(Changing(the(temperature(will(change(the(retention(

time(of(all(of(the(alkanes(

149



A student used paper chromatography to separate two components, I and II, in a solution. A spot of the solution was initially placed at the origin. When the spot corresponding to component I (Rf = 0.50) had advanced 4.0 cm, the spot corresponding to component II was 1.0 cm behind. The Rf value of component II is closest to

QUESTION 1

(VCAA Q6 June 2006)

A. 0.68

B. 0.38

C. 0.25

D. 0.13



A student used paper chromatography to separate two components, I and II, in a solution. A spot of the solution was initially placed at the origin. When the spot corresponding to component I (Rf = 0.50) had advanced 4.0 cm, the spot corresponding to component II was 1.0 cm behind. The Rf value of component II is closest to

QUESTION 1 (ANSWER)

A. 0.68

B. 0.38

C. 0.25

D. 0.13 The answer is alternative B First we need to calculate the distance that the solvent had travelled.

Since Rf We can calculate that the distance travelled by the solvent

So now we can find the Rf of component II which travelled only 3.0 cm = = 8.0cm (1.0 cm behind component I) Rf = = 0.375=0.38 (to 2 sig figs) (VCAA Q6 June 2006)

4.00.50

3.08.0



QUESTION 2 Chromatogram 1 was obtained by analysis of a sample of a mixture of two sugars, A and B, using high performance liquid chromatography (HPLC). Chromatogram 2 was obtained by analysing another sample of the same mixture by HPLC under different conditions. Consider the following changes, which could be made to the operating conditions for HPLC. I decreasing the pressure of the mobile phase II decreasing the temperature III using a less tightly packed column Which of the changes would be most likely to produce chromatogram 2?

(VCAA Q5 June 2007)

A. I only

B. II only

C. III only

D. I and II only



QUESTION 2 (ANSWER) Chromatogram 1 was obtained by analysis of a sample of a mixture of two sugars, A and B, using high performance liquid chromatography (HPLC). Chromatogram 2 was obtained by analysing another sample of the same mixture by HPLC under different conditions. Consider the following changes, which could be made to the operating conditions for HPLC. I decreasing the pressure of the mobile phase II decreasing the temperature III using a less tightly packed column Which of the changes would be most likely to produce chromatogram 2?



The answer is alternative C (III only). The retention times in chromatogram 1 are greater than those in chromatogram 2, so changes which slow the progress of the mixture will result in chromatogram 1 and those that speed it up will result in chromatogram 2. Decreasing the pressure of the mobile phase will slow down the progress of the components through the column, so this will match chromatogram 1, not 2 Decreasing the temperature of the column will also slow down the progress of the components (chromatogram 1) Using a less tightly packed column will allow the components to move more quickly through the column so this will result in chromatogram 2.

(VCAA Q5 June 2007)

A. I only

B. II only

C. III only

D. I and II only



QUESTION 3

(VCAA Q6 June 2010)

A. 0.29

B. 0.62

C. 0.78

D. 0.80

Consider the following TLC plate of compounds X, Y and Z developed using a suitable mobile phase on a polar stationary phase. The Rf value of the most polar component in this TLC separation is:



QUESTION 3 (ANSWER)

A. 0.29

B. 0.62

C. 0.78

D. 0.80

Consider the following TLC plate of compounds X, Y and Z developed using a suitable mobile phase on a polar stationary phase. The Rf value of the most polar component in this TLC separation is:

The answer is alternative A The question states that the stationary phase is polar, so the most polar component will have the greatest attraction to the stationary phase and will take the longest to move along the TLC plate. It will have the smallest Rf value. It is component X that travels only 0.80 cm (BUT this is not its Rf) Rf (VCAA Q6 June 2010)



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Atomic Absorption Spectroscopy

CHEMISTRY



Key(Knowledge(

Principles(and(applications(of(spectroscopic(

techniques((excluding(features(of(instrumentation(

and(operation),(and(interpretation(of(qualitative(

and(quantitative(data(from:(

! atomic(absorption(spectroscopy((AAS)(including(electron(transitions(and(use(of(calibration(graph(

to(determine(amount(of(analyte(

! visible(and(ultraviolet(spectroscopy((visiblePUV)(including(electron(transitions(and(use(of(

calibration(graph(to(determine(amount(of(analyte(

(



The&electromagnetic&spectrum(

•  Radiation(in(the(electromagnetic(spectrum(has(a(range(of(differing(energies.(



Wavelength&and&energy&

! Wavelength(is(the((distance(between((

adjacent(crests(of(the((

electromagnetic(wave(

! The(shorter(the(wavelength,(the(greater(its(energy(

! Wavelength(is(related(to(energy(by((((((Where(c(is(the(speed(of(light,(h(is(Planck’s(constant(

and(λ(is(the(wavelength.(

hcλ

E =



•  Depending(on(its(energy,(radiation(may(have(varying(effects(on(a(

substance(

•  Ultraviolet(and(visible(radiation(is(absorbed(by(a(compound(and(excites(

the(electrons(of(a(molecule.((

•  The(absorption(of(infrared(radiation(causes(a(molecule(to(vibrate.(



Atomic&emission&spectra&! Heat,(ligh(t(or(electricity(can(excite(the(electrons(of(an(atom(to(higher(energy(

levels(

! An(emission(spectrum(is(formed(when(the(excited(electrons(fall(back(from(higher(

energy(levels(to(the(2nd(electron(shell.(

! Each(line(corresponds(to(radiation(of(a(speci@ic(energy((and(wavelength).(

! The(combination(and(energy(of(lines(is(speci@ic(to(an(element,(like(a(@ingerprint(



Atomic(absorption(spectroscopy(

•  The(light(source((hollow(cathode(lamp)(is(created(by(using(the(light(emitted(by(excited(atoms(of(an(element,(making(it(speci@ic(to(the(element.(

•  The(strongest(line(in(the(emission(spectrum(is(chosen(for(analysis.(



!  Sample(solution(of(very(low(concentration(is(‘aspirated’(into(high(temperature(@lame(

where(it(meets(the(light(from(the(emission(

lamp.(

!  Sample(absorbs(light(!  The(greater(the(concentration(of(the(

element(that(is(present,(the(more(light(is(

absorbed.(

!  Light(that(passes(through(sample(is(detected(and(compared(to(incident(light(

!  Percentage(absorbance(is(recorded.(



ApplicaFons&

! Analysis(of(metals(in(very(low(concentrations.(

! Low(concentrations(are(measured(in(parts(per(million((ppm)(=(mg(per(L(of(solution((

(or(parts(per(billion((ppb)(=(µg(per(L(of(solution(

! Eg(concentration(of(heavy(metal(such(as(mercury(or(lead(in(water,(or(in(@ish,(or(concentration(of(sodium(in(sports(drink(

! Is(a(speci@ic(form(of(analysis(–(you(have(to(know(what(you(are(looking(for.((



Obtaining(Quantitative(results(

•  Standard(solutions(with(known(concentrations(of(the(element(are(measured(

and(results(used(for(calibration(graph.(



AAS(sample(exam(question(

This(is(a(calibration(curve(for(Ba2+(ions(in(an(

Atomic(Absorption(Spectrometer(

(a)  If(the(absorbance(of(a(solution(is(0.11,(@ind(the(

concentration(of(Ba2+(

ions(in(the(solution(

(b) Calculate(the(mass(of(Ba2+(ions(in(10(mL(of(this(solution(




Answer(

a)  Using(the(graph,(an(absorbance(of(0.11(corresponds(to(a(concentration(of(19(

mgLP1(

b)  Concentration(=((((((((mass(=(concentration(×(volume(

(((((((((((((((((((((((((=(19(×(0.010(

((((((((((((((((((((((((((=((0.19(mg(

massvolume



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UV-Visible Spectroscopy

CHEMISTRY



UVBVisible&Spectroscopy&

•  Radiation(in(the(UV(and(visible(parts(of(the(spectrum(has(quite(high(energy(

•  It(is(able(to(be(absorbed(by(atoms,(ions(or(molecules(and(excites(the(electrons(in(the(

compounds(from(low(energy(levels(to(

higher(energy(levels.(



! Different(substances(have(many(different(energy(levels,(so(the(energy(and(wavelength(of(the(light(required(to(promote(the(electrons(vary.(&

! If(a(substance(absorbs(visible(light,(it(will(appear(coloured.(

! The(colour(of(light(that(is(absorbed(is(the(complementary(colour(to(that(shown(by(the(compound(eg(red(is(the(complementary(colour(of(blue,(so(blue(solutions(will(absorb(red(light.(



How(does(it(work?((

•  Light(of(a(selected(wavelength(is(shone(through(a(sample.(

•  The(amount(of(light(that(is(transmitted((goes(through(the(sample)(is(measured:(%(

transmittance.(



Quantitative(use(of(UVPVis(Spec(

! The(relative(absorbances(of(wavelengths(from(200nm(to(800nm(is(measured(for(the(

compound.(

! Wavelength(of(light(that(is(strongly(absorbed(by(compound(is(selected(for(

quantitative(use.(

&



CalibraFon&graph&

•  As(for(AAS,(a(calibration(graph(is(created(by(measuring(the(%(transmittance(of(a(series(of(samples(of(known(concentration(and(plotting(the(two(quantities(against(each(other.(

•  A(straight(line(is(obtained.(•  The(%(transmittance(of(the(sample(is(measured(and(its(concentration(is(found(from(the(calibration(graph.(



ApplicaFons&of&UVBVis&

! Clinical(analysis(eg(determining(the(haemoglobin(content(and(sugar(levels(in(blood(

! Identifying(the(presence(of(elements(by(converting(them(into(coloured(compounds(if(

they(are(not(already(coloured(

! Determining(the(levels(of(nutrients,(additives(and(contaminants(in(water(and(foods(

! Quantitative(analysis(of(DNA(and(proteins(



UVPVis((sample(exam(question(The(UVPvisible(absorption(spectrum(of(a(solution(of(paracetamol(is(shown(below.(The(concentration(of(paracetamol(in(the(solution(is15.1(µg(mLP1((

(

(

(

(

(

The(absorbance(of(another(solution(of(paracetamol(is(measured(under(the(same(conditions,(and(at(245(nm,(the(absorbance(is(0.96.(What(is(the(concentration,(in(µg(mLP1(

of(the(paracetamol(in(this(other(solution?(




Answer(

The(UVPvisible(spectrum(shows(an(

absorbance(of(1.6(for(the(concentration(of(

15.1µg(mLP1(

Therefore,(if(the(absorbance(is(0.96,(we(can(

@ind(the(concentration(

(using(the(ratio(of((

concentration(to((

absorbance(

( -1

15.11.6 0.96

15.10.961.6

9.1 gmL

x

x

µ

=

= ×

=



Which one of the following analyses is best performed using atomic absorption spectroscopy?

QUESTION 1

(VCAA Q2 June 2007)

A. Measuring the amount of potassium in salt B. Determining the amount of caffeine in coffee C. Measuring the carbonate content of mineral water D. Detecting the presence of ethanoic acid in a sample of wine.



Which one of the following analyses is best performed using atomic absorption spectroscopy?

QUESTION 1

A. Measuring the amount of potassium in salt B. Determining the amount of caffeine in coffee C. Measuring the carbonate content of mineral water D. Detecting the presence of ethanoic acid in a sample of wine.



Atomic absorption spectroscopy (AAS) is always used to determine concentration of metals in solution. Each of the four alternatives should be considered with this in mind. In B and D the substances that are being analysed are organic (Carbon-based). There is no metal present in them, so AAS cannot be used. In alternative C, while the carbonate ion (CO3

2-) must have been accompanied by a metal ion, it is the carbonate content that needs to be measured, so AAS is not valid. Alternative A refers to a metal (potassium) present in salt, so this is the correct answer.

(VCAA Q2 June 2007)



A sodium lamp emits a yellow-coloured light. If the light from the lamp was passed through a container of sodium vapour, it is likely that the light emerging from the container would appear

QUESTION 2


A. brighter due to electrons in atoms in the sodium vapour moving from higher to lower energy levels.

B. brighter, due to electrons in atoms in the sodium vapour moving from lower to higher energy levels.

C. duller, due to electrons in atoms in the sodium vapour moving from higher to lower energy levels.

D. duller, due to electrons in atoms in the sodium vapour moving from lower to higher energy levels.



A sodium lamp emits a yellow-coloured light. If the light from the lamp was passed through a container of sodium vapour, it is likely that the light emerging from the container would appear

QUESTION 2 (ANSWER)

A. brighter due to electrons in atoms in the sodium vapour moving from higher to lower energy levels.

B. brighter, due to electrons in atoms in the sodium vapour moving from lower to higher energy levels.

C. duller, due to electrons in atoms in the sodium vapour moving from higher to lower energy levels.

D. duller, due to electrons in atoms in the sodium vapour moving from lower to higher energy levels.



The correct answer is D: duller, due to electrons in atoms in the sodium vapour moving from lower to higher energy levels. The light being emitted by the sodium lamp has the energy that is needed by a sodium atom to excite its electrons from lower energy levels to higher energy levels. When this light is passed through a container of sodium vapour, the sodium atoms will absorb some of this light energy and so the light emerging from the container will be duller. The reason is that the atoms in the sodium vapour are using that light energy to move from lower to higher energy levels.




An experiment was carried out to determine the percentage of manganese in a particular sample of steel. A 13.936g of steel was dissolved in acid and the manganese was converted to MnO4

-(aq) ions. The solution containing the MnO4-(aq) ions was filtered and made up to a

volume of 1.00 L. 25.00 mL of this solution was then further diluted to 100.0 mL in a volumetric flask. The absorbance, at 525 nm, of this solution was 0.70.

QUESTION 3(a)

(VCAA Q2 June 2008)

Next, the absorbance, at 525 nm, of a series of solutions of MnO4

-(aq) ions of known concentration was measured and a calibration graph drawn.

What is the concentration, in mgL-1, of MnO4

-(aq) in the diluted solution in the 100 mL volumetric flask? Concentration = mgL-1









What is the concentration, in mgL-1, of MnO4

-(aq) in the diluted solution in the 100 mL volumetric flask?



The concentration of MnO4-(aq) in the diluted solution in the 100 mL volumetric flask is

35 mgL-1 The calibration graph directly gives us the concentration, in mgL-1, of the diluted sample. You need to find the absorbance (0.70) on the vertical axis and carefully draw a horizontal line across to the calibration graph and from that point draw a vertical line down to the concentration axis.

The value that you read should be 35 mgL-1.

(VCAA Q2 June 2008)






QUESTION 3(b)

(VCAA Q2 June 2008)



Calculate the mass, in mg, of manganese in the steel sample. Mass = mg









Calculate the mass, in mg, of manganese in the steel sample.



Note in reading the question that the g of steel was dissolved and made up to L ( mL). Then mL of this solution was then diluted to mL (a dilution) and it was for this diluted sample that we found the concentration to be mgL-1 The mL of diluted solution contained MnO4

- at a concentration of mgL-1. The concentration of MnO4

- in the original solution is mgL-1 Since the volume of the original solution was L, the mass of MnO4

- in the original solution = mg n(MnO4

-) mol n(Mn) in the 1.00L of steel solution m(Mn) g mg

(VCAA Q2 June 2008)

10025

0.140(54.9+ 4×16.0)

0.140118.9



Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/infrared-spectroscopy/key-knowledge/


Infrared Spectroscopy

CHEMISTRY



Key(Knowledge(

•  infrared(spectroscopy((IR)(including(use(of(characteristic(absorption(bands(to(

identify(bonds(

•  mass(spectroscopy(including(determination(of(molecular(ion(peak(and(

relative(molecular(mass,(and(identi@ication(

of(simple(fragments(

&



Key(knowledge(continued(

•  proton(and(carbonP13(nuclear(magnetic(resonance(spectroscopy((NMR)(including(spin,(

the(application(of(carbonP13(to(determine(

number(of(equivalent(carbon(environments;(

and(application(of(proton(NMR(to(determine(

structure:(chemical(shift,(areas(under(peak(and(

peak(splitting(patterns((excluding(coupling(

constants),(and(application(of(n+1(rule(to(

simple(compounds(



Infrared((IR)(Spectroscopy((

•  Recall(that(infrared(radiation(has(a(longer(wavelength(and(lower(energy(than(visible(

light.(

•  Infrared(radiation(can(be(absorbed(by(molecules(and(makes(the(bonds(in(the(

molecules(vibrate(more(than(they(are(

already.(



•  Bonds(within(molecules(can(vibrate(in(a((((((((((variety(of(ways.(((

• (Each(of(these(different(types(of(vibration(result(when(infrared(radiation(of(different(

frequencies(is(absorbed.(



How&an&infrared&spectrometer&

works&&



Factors&which&affect&the&frequency&of&

radiation&absorbed&include:&

! 'Strength(of(the(bond.&&&&&&As(the(strength(of(the(bond(increases,((((

(((frequency(increases.(

! !Mass(of(atoms(in(the(bond.&&&&&&&As(the(masses(of(the(atoms(increase,((((

((((the(frequency(decreases.(

&



Reminders&about&waves:&

•  All(wavelengths(of(electromagnetic(radiation(travel(at(the(same(speed(

•  Frequency(∝(1(/(wavelength(•  In(infrared(spectroscopy,(radiation(absorbed(is(identi@ied(by(

wavenumber(which(is(measured(in(

cmP1((a(type(of(frequency)(



Two&ways&in&which&an&infrared&

spectrum&may&be&used:&

! The(wavenumber(of(the(bands((peaks)(is(used(to(identify(particular(functional(groups(

! The(‘@ingerprint’(region(may(be(matched(to(that(of(another(infrared(spectrum.(

! An(unknown(compound(can(be(identi@ied(if(its(spectrum(matches(exactly(that(of(a(known(compound.(



General'points'to'note'about'IR'spectra'(eg'ethanol)'

'yPaxis(

xPaxis(has(highest(wavenumber(on(the(left(

Bands(go(downward,(since(all(absorption(amounts(to(less(than(100%(transmittance.(



Identi;ication&of&functional&groups&&

See&Table&7&p7&VCE&Data&booklet&



Identi;ication&of&functional&groups&

! Look(for(C=O(band(at(1670P1750(cmP1(

! If(C=O(band(is(missing,(then(it(is(not(a(carboxylic(acid(or(ester(

! Look(for(OPH(band(at(2500P3300(cmP1(((if(C=O(present)(or(at(3200P3550(cmP1((

(if(C=O(not(present(=(alcohol)(

! Expect(to(@ind(CPH(band(at(((((2850P3300(cmP1(

! Maybe(CPCl(band(at(700P800(cmP1(

&



The&;ingerprint&region&

•  This(is(the(region(of(a(spectrum(below(1500(cmP1.(((

•  Lots(of(peaks(here(–(do(not(try(to(identify(all!(

•  Use(this(region(to(identify(unknown(compounds(by(matching(their(spectra(with(those(of(known(ones.(



Ethanoic'acid'



Ethyl'ethanoate'(an'ester)'



•  Infrared(spectra(cannot(usually(be(used(in(isolation(to(completely(identify(

unknown(compounds.(

•  Instead,(they(are(used(in(combination(with(other(techniques(such(as(mass(

spectroscopy(and(nuclear(magnetic(

resonance(spectroscopy.(



What&functional&group/s&is/are&

present&here?&



What&do&you&see&in&this&spectrum?&



And&this&one?&



IR(sample(exam(question(

When(a(sample(absorbs(infrared(radiation(

A.  Covalent(bonds(are(broken(B.  Covalent(bonds(stretch(and(vibrate(C.  The(spin(alignment(of(certain(nuclei(

changes(

D.  Electrons(in(atoms(move(to(higher(energy(levels(




Answer(

B(is(the(answer(

Infrared(radiation(is(not(high(enough(in(

energy(to(break(covalent(bonds((alternative(

A),(but(it(will(cause(bonds(to(stretch((a(form(

of(vibration)(

UV(radiation(can(cause(electrons(to(change(

energy(levels((C)(

Radio(frequencies(cause(changes(to(the(spin(

alignment(of(nuclei((D)(

(




Mass Spectrometry

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/mass-spectrometry/mass-spectrometry/

CHEMISTRY



Mass&Spectrometry&&&•  Mass(spectrometry(is(used(to(

describe(the(structure(of(a(molecule((

•  The(molecule(breaks(into(‘fragments’(in(the(mass(spectrometer.(

•  Previously(we(have(only(used(a(mass(spectrometer(for(determining(the(

masses(and(abundances(of(isotopes.(



Diagram&of&a&mass&spectrometer&



How(are(fragments(formed?(

•  For(organic(compounds,(during(ionisation,(the(high(energy(electrons(also(cause(parts(of(the(

molecule(to(break(off((fragments).(

•  There(will(be(some(whole(molecules(present(as(ions((the(molecular(ion)(and(also(fragments(

which(correspond(to(parts(of(the(molecule(eg(

CH3+,(CH3CH2

+(etc(

•  Each(positively(charged(fragment(appears(as(a(peak(on(the(mass(spectrum(for(the(compound.(

&&



A(mass(spectrum(

(Propanoic(acid)((



Use'of'mass'spectra'in'analysis'

! The(sizes(of(the(fragments(can(help(us(identify(the(structure(of(a(compound,(

! Other(information(is(used(in(conjunction:(

◦  ((empirical(formula((from(calculations)(◦  ((functional(groups(present((IR((((((((((spectroscopy)(

◦  (details(of(the(arrangment(of(hydrogens(in(the(compound((NMR(spectroscopy).(



Useful(fragments(to(look(for(

! Molecular(ion((M+)(

◦ This(is(usually(the(peak(with(the(greatest(m/e(ratio(on(the(spectrum.(

◦ It(gives(you(the(molecular(mass(of(the(compound(which(can(be(combined(with(

the(empirical(formula(to(@ind(the(

molecular(formula.(



! Peaks(due(to(common(groups(in(organic(compounds(

! m/e(=(15( ( (CH3+(((methyl)(

! m/e(=(29( (CH3CH2+(((ethyl)(

! m/e(=(45( (COOH+(((carboxyl)(

(



Mass(spectrum(of(propanP1Pol(



Another(example(–(ethanol,(C2H5OH(



Mass(spec(sample(exam(question(

A(sample(of(compound(M(is(analysed(in(a(mass(spectrometer(where(it(forms(the(molecular(ion(M+(according(to(

M((+((eP((→(M+(+(2eP(

Some(of(the(molecular(ions(fragment(as(follows:(

M+(→(A+(+(B((and(M+((→ A(+(B+(The(mass(spectrum(would(show(peaks(due(to(the(species(

A.((M+,(A,(A+,(B(and(B+(only(((B.(((M+,(A+(and(B+(only(

C.(((A+(and(B+(only(( (((((((((D.((A(and(B(only(




Answer(

B(is(the(answer(

This(is(the(only(alternative(with(parts(of(the(

answer(being(positively(charged(particles(



The molecules ethanol and nitrogen dioxide have the same molar mass (M = 46 g mol–1). They can be easily distinguished by mass spectrometry. The mass spectra of the two molecules are shown below.

QUESTION 1

(VCAA June 2010 Section B Q3)

Write an equation showing how either an ethanol molecule or a nitrogen dioxide molecule becomes ionised in the mass spectrometer.

Please write down the equation on a piece of paper. You can self-mark it using the answer on the next slide.




QUESTION 1 (ANSWER)

Write an equation showing how either an ethanol molecule or a nitrogen dioxide molecule becomes ionised in the mass spectrometer.



Many different equations were possible and acceptable as answers for this question. CH3CH2OH(g) + e- � [CH3CH2OH]+(g) + 2e- Or CH3CH2OH(g) � CH3CH2OH+(g) + e- Or C2H6O(g) � C2H6O+(g) + e- Or NO2(g) + e- � [NO2]+(g) + 2e- Or NO2(g) � NO2

+(g) + e- The important part of the question is that the molecule is being ionised, so an electron must be given off as a product and the product particle must have a positive charge. There is no need for the molecule to be fragmented (broken by the impact of the electron), as the question asks for the equation to show how the ethanol or nitrogen dioxide molecule is ionised, not fragmented. It is important to show the states of the molecules as gaseous (g), since the first thing that happens to a sample in the mass spectrometer is that it is vaporised to the gaseous phase.

(VCAA Section B Q3 June 2010)




QUESTION 2(a)

Which mass spectrum cannot be that of nitrogen dioxide? cannot be that of nitrogen dioxide.






Which mass spectrum cannot be that of nitrogen dioxide?

Spectrum A cannot be that of nitrogen dioxide.





QUESTION 2(b)

What evidence does the mass spectrum provide to support your answer?

Please write down your explanation on a piece of paper. You can self-mark it using the answer on the next slide. (VCAA June 2010 Section B Q3)





What evidence does the mass spectrum provide to support your answer?

There are only 3 possible peaks for NO2 – m/e = 16 (O+), 30 (NO+) or 46(NO2+)

Peaks at m/e = 45 (or 31 or 29 or 27) will not result from fragmentation of NO2 or the NO2 molecule.





QUESTION 3

What is the formula of the species that produces the peak seen at m/z 30 in spectrum B?

Please write down the formula on a piece of paper. You can self-mark it using the answer on the next slide. (VCAA June 2010 Section B Q3)




What is the formula of the species that produces the peak seen at m/z 30 in spectrum B?


QUESTION 3 (ANSWER)

Spectrum B is the mass spectrum of NO2. The m/z value of 30 corresponds to one N (14) and one O(16) 14 + 16 = 30, so the acceptable answers are [NO]+ or NO+ or NO�+




NMR Spectroscopy

Theory, Spin and H Environments

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/nmr-spectroscopy-theory-spin-h-environments/nmr-spectroscopy/

CHEMISTRY



Nuclear(magnetic(resonance((NMR)(

spectroscopy(! This(is(used(to(identify(the(arrangement(of(hydrogen(atoms(in(a(compound.(

•  It(is(possible(because(1H(nuclei(have(a(‘spin’(of(½(13C(also(has(a(spin(of(½(so(

can(also(be(analysed(using(NMR((also(31P,(19F(and(15N)(



What&is&Spin?&

•  Spin(is(a(fundamental(property(of(nature(like(electrical(charge(or(mass.(

•  (Spin(comes(in(multiples(of(1/2(and(can(be(+(or(P.(

•  A(nucleus(with(a(((((nonPzero(spin((

(((behaves(like(a((

(((small(magnet((



How&does&it&work?&

! An(NMR(spectrometer(applies(a(large(magnetic(@ield((about(10(000(times(that(of(earth’s(magnetic(@ield)(to(the(sample.(

! The(spinning(1H(nuclei(respond(by(either(aligning(with(the(magnetic(@ield(or((opposing((it.(‘Spin(up’(or(‘spin(down’)(



Two(energy(levels((‘spin(states’)(exist(

for(a(spinning(nucleus,(the(lower(one(

being(when(the(nucleus(is(aligned(

with(the(external(magnetic(@ield.(

E

ΔE=hν

BBapp

µ opposedto B

µ alignedwith B



•  When(a(magnetic(@ield(is(being(applied(to(an(1H(nucleus((a(‘proton’)(the(difference(

between(the(spin(states(is(still(quite(small.(

•  So,(radiowaves((low(energy)(provide(enough(energy(to(excite(a(proton(from(one(

spin(state(up(to(the(other((for(it(to(resonate)(

•  Only(1H(NMR(and(13C(NMR(have(to(be(analysed(in(this(course(

•  13C(NMR(spectra(have(a(very(different(scale(to(1H(NMR(spectra((



Magnetic(in@luences(on(an(atom(in(a(

compound.(•  The(applied(magnetic(@ield((Bapp)(comes(from(the(actual(NMR(instrument(

•  A(local(magnetic(@ield(is(due(to(other(atoms(in(the(compound.(

•  The(local(@ield((as(experienced(by(1H(nuclei(in(a(compound)(depends(on(their(

‘environment’(



•  The(environment(of(the(1H(is(made(up(of(the(atom(it(is(bonded(to,(as(well(as(other(

atoms(nearby.(

•  These(change(the(way(a(1H(nucleus(responds(to(the(applied(magnetic(@ield.(

•  A(H(bonded(to(an(O(in(OH(will(resonate(at(a(different(energy(to(one(bonded(to(a(C(

(eg(in(CH3)(



Example&of&an&NMR&spectrum&




Analysing NMR Spectra

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/aos-1-chemical-analysis/analysing-nmr-spectra/how-can-we-use-nmr/#watch

CHEMISTRY



How&can&we&use&NMR?&

•  The(NMR(spectrum(is(made(up(of(sets(of(peaks(

•  The(position(of(a(peak(depends(on(the(environment(of(the(1H(nuclei(producing(that(peak.(

•  The(position(of(the(peak(along(the(horizontal(axis(is(known(as(chemical(shift.&



•  The(location(of(an(NMR(signal(in(a(spectrum(is(measured(relative(to(a(reference(signal(from(a(reference(compound(added(to(the(sample.(

•  The(protons(in(the(reference(compound,(TMS,(tetramethylsilane,(Si(CH3)4,(are(assigned(a(chemical(shift(of(zero.(((

((((this(will(always(be((

((((present,(but(does(not(

((((�count�(as(a(peak)(•  A(chemical(shift(of(((((1(ppm(means(that((

(((the(signal(is(shifted(by(200(Hz(on(a(200MHz(((

(((instrument.(



•  H(atoms(bonded(to(more(electronegative(atoms(will(have(a(

greater(shift((further(to(left)(than(those(

in(more(electron(dense(environments.(

•  Eg(a(H(bonded(to(an(O(will(have(a(greater(shift(than(one(bonded(to(C(

•  Tables(of(chemical(shifts(help(us(to(identify(a(H(atom(–(See(table(5(in(Data(

booklet(



p5 of data booklet

Also see p6 of data booklet



The(size(of(peaks(

•  The(size(of(peaks(relative(to(each(other(is(often(indicated(by(an(integration(

trace.(

•  The(ratio(of(the(areas(under(the(peaks((from(the(integration(trace)(gives(the(

ratio(of(H(atoms(of(a(particular(‘type’(



example(

•  In(CH3CH2CH2CH3(there(are(two(different(environments(for(Hs.(They(may(either(be(part(of(a(CH3(group(or(a(CH2(group.(

•  So(there(will(be(two(peaks(on(the(NMR(spectrum(for(butane(–(one(at(chemical(shift(of(0.9(ppm((for(CH3(groups)(and(the(other(at(chemical(shift(of(1.3(ppm(for(RPCH2PR(.(



•  An(integration(trace(of(these(peaks(will(show(a(ratio(of(peak(areas(of((

(((3(:(2(re@lecting(the(ratio(of(Hs(in(CH3((((

(((groups(to(Hs(in(CH2(groups.(



Ethanol&–&3&environments&



SpliFng'of'peaks''(high'resolu:on'NMR)'

•  The(effect(of(neighbouring(1H(nuclei(is(to(split(the(peak(corresponding(to(a(

particular(group(of(Hs(into(several(

small(peaks.((

•  This(effect(is(called(a(splitting(pattern.(



•  Eg(If(the(Hs(in(a(CH3(group(on(the(end(of(a(molecule(has(a(neighboring(C(with(

2Hs(on(it,(the(peak(for(the(CH3(Hs(will(

be(split(into(three((a(triplet).((n(+(1(

rule)(

Triplet would represent these Hs Due to the 2 neighbouring Hs



•  In(the(example(of(butane,(the(peak(at(0.9ppm((CH3(peak)(would(be(a(triplet(because(it(would(be(split(by(

the(neighboring(group(of(two(Hs(on(CH2(

•  The(peak(at((1.3ppm((due(to((

CH2)(would(be(a((

multiplet(due(to((

the(3(neighboring((

CH3(Hs(AND(the((

2(neighbouring((

CH2(Hs(



Chloroethane(–(2(environments,(one(

triplet(and(one(quartet(



13C(NMR(

! 13C(is(a(naturally(occurring,(but(very(low(concentration(isotope(of(carbon.(

! It(can(be(used(for(identifying(the(different(carbon(environments(in(a(

molecule.(

! Chemical(shifts(are(much(greater(for(13C(NMR(than(1H(NMR((up(to(200(ppm)(

! 13C(NMR(spectra(tend(to(be(simpler(than(1H(due(to(the(smaller(differences(

between(Cs.(



13C(NMR(of(ethanol(

! Notice(that(there(are(only(2(peaks(since(there(are(only(2(different(Cs((one(on(end(

and(one(in(middle)(

! There(is(no(splitting(in(a(13C(NMR(&



In(summary(! Chemical(shift(provides(information(about(the(position(in(the(molecule(in(which(the(H(is(found.(

! Number(of(peaks(=(number(of(different(environments(

! Peak(area(gives(information(about(the(ratio(of(equivalent(Hs(

! Peak(splitting(gives(information(about(the(number(of(neighbouring(Hs.(



NMR(Sample(exam(question(

A(sample(of(a(hydrocarbon(for(analysis(is(placed(in(a(strong(magnetic(@iled(and(irradiated(with(electromagnetic(radiation(of(radio(wave(frequency.(This(is(most(likely(to(result(in(

(((((A. (ionisation(and(fragmentation(of(molecules(

(((((B.((An(increase(in(bond(vibrations(of(molecules(

(((((C.((The(promotion(of(electrons(to(higher(energy(((

(((((((((((levels(

(((((D.((A(change(in(the(energy(of(the(nuclei(of(the((

(((((((((((hydrogen(atoms.(

(VCAA(June(2008(Q(15)(



Answer(

D(describes(NMR(

A(describes(mass(spectroscopy(

B(describes(IR(spectroscopy(

C(describes(atomic(emission(spectroscopy(



The disease sickle cell anaemia is marked by the presence of an abnormal protein in the blood of people with this disease. The sixth position in the normal protein chain is occupied by the amino acid, glutamic acid. The sickle cell protein chain has the amino acid, valine, in the sixth position. This is the only difference between the two protein chains. A section of each protein chain containing glutamic acid and valine is shown below.

QUESTION 1



It is possible to determine the molecular mass of these proteins in a mass spectrometer. It is also possible to record their 1H NMR spectra. Which one of the following alternatives is correct?

Molecular mass 1H NMR spectrum A. Sickle cell protein chain has the

greater molecular mass. Both protein chains have the same 1H NMR spectrum.

B. Sickle cell protein chain has the greater molecular mass.

The protein chains have different 1H NMR spectra.

C. Normal protein chain has the greater molecular mass.

Both protein chains have the same 1H NMR spectrum.

D. Normal protein chain has the greater molecular mass.


(VCAA June 2008 Q5)



The disease sickle cell anaemia is marked by the presence of an abnormal protein in the blood of people with this disease. The sixth position in the normal protein chain is occupied by the amino acid, glutamic acid. The sickle cell protein chain has the amino acid, valine, in the sixth position. This is the only difference between the two protein chains. A section of each protein chain containing glutamic acid and valine is shown below.

QUESTION 1 (ANSWER)



It is possible to determine the molecular mass of these proteins in a mass spectrometer. It is also possible to record their 1H NMR spectra. Which one of the following alternatives is correct?

Molecular mass 1H NMR spectrum

A. Sickle cell protein chain has the greater molecular mass.


B. Sickle cell protein chain has the greater molecular mass.


C. Normal protein chain has the greater molecular mass.


D. Normal protein chain has the greater molecular mass.




The difference between the two protein chains is the different amino acid in the 6th position. Normal protein has glutamic acid and the sickle cell protein has valine. From the Chemistry Data Book we see that the structures of the two differing amino acids are

Glutamic acid has a larger molar mass than valine, so the Normal protein chain would have a greater molecular mass. Because the 1H environments are different in glutamic acid (3 environments) compared to valine (2 environments), the protein chains would have different 1H NMR spectra.

(VCAA June 2008 Q5)

The correct answer is D.



The polymer polylactic acid, PLA, shown above, is used to make soluble stitches which are absorbed by the body following surgery. Other than the peak given by the TMS reference, the monomer from which PLA is formed would give

QUESTION 2

(VCAA June 2009 Q4)

A. one set of peaks in the 1H NMR spectrum B. two sets of peaks in the 1H NMR spectrum C. three sets of peaks in the 1H NMR spectrum D. four sets of peaks in the 1H NMR spectrum



The polymer polylactic acid, PLA, shown above, is used to make soluble stitches which are absorbed by the body following surgery. Other than the peak given by the TMS reference, the monomer from which PLA is formed would give

QUESTION 2 (ANSWER)

A. one set of peaks in the 1H NMR spectrum B. two sets of peaks in the 1H NMR spectrum C. three sets of peaks in the 1H NMR spectrum D. four sets of peaks in the 1H NMR spectrum



The section of the polymer, polylactic acid, shown in the question shows repeating ester groups –COO- which can be used to identify the monomer from which the condensation polymer is produced. The ester groups form by reaction between carboxyl and hydroxyl groups, so we would expect a carboxyl group on the right hand end of the monomer and a hydroxyl on the left hand end of the monomer.

The monomer would look like this:

It is lactic acid, although this knowledge is not necessary to answer the question correctly. It would have four hydrogen environments. Since each 1H environment is represented by a peak, the correct answer is D.

(VCAA June 2009 Q4)



The structure of an organic molecule, with empirical formula CH2O, is determined using spectroscopic techniques. The molecular formula of this molecule is C2H4O2. The infrared spectrum and 1H NMR spectrum for this molecule are given below.

QUESTION 3(a)

(VCAA June 2009 Section B Q5 (modified))

How many different proton environments are there in this molecule? There are different proton environments.






How many different proton environments are there in this molecule? Because there are two peaks in the NMR spectrum, there must be two different proton (1H) environments.




QUESTION 3(b)

Draw the structure of the unknown molecule, clearly showing all bonds. Please draw your answer on a piece of paper. You can self-mark it using the answer on the next slide.






Draw the structure of the unknown molecule, clearly showing all bonds.



(colour is not important for this answer) (VCAA June 2009 Section B Q5 (modified))




QUESTION 3(c)

Explain how the structure of the compound you have drawn in part (b) is consistent with its IR spectrum.

Please write your explanation on a piece of paper. You can self-mark it using the answer on the next slide. (VCAA June 2009 Section B Q5 (modified))




QUESTION 3(c) (ANSWER)

Explain how the structure of the compound you have drawn in part (b) is consistent with its IR spectrum.



There is a strong band at 1750 cm-1 which indicates that there is a C=O (carbonyl) group. And there is a broad band at 2500-3300 (cm-1) indicating an O-H bond. Together these two bands confirm the existence of the carboxyl functional group.





QUESTION 3(d)

Name the compound you have drawn in part (b).

Enter your answer here: (VCAA June 2009 Section B Q5 (modified))




QUESTION 3(d) (ANSWER)

Name the compound you have drawn in part (b).



Ethanoic acid (Eth – 2 carbons, -oic acid due to the carboxyl functional group)





Exam Question Combining Spectroscopic Techniques

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CHEMISTRY



Exam(question(that(combines(all(

three(techniques(The(structure(of(an(organic(molecule,(with(

empirical(formula(CH2O,(is(determined(

using(spectroscopic(techniques.(The(mass(

spectrum,(infrared(spectrum(and(1H(NMR(

spectrum(for(this(molecule(are(given(below.(

Use(the(information(provided(by(these(

spectra(to(answer(these(questions.(



a) What(is(the(molecular(formula(of(this(molecule?(

b) How(many(different(proton(environments(are(there(in(this(molecule?(

c)  Draw(the(structure(of(the(unknown(molecule,(clearly(showing(all(bonds.(




Calculations

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CHEMISTRY



Key(Knowledge(

•  calculations(including(amount(of(solids,(liquids(and(gases;(concentration;(volume,(

pressure(and(temperature(of(gases(



Revision(of(Unit(2(

•  When(working(out(what(formula(to(use(in(calculations(classify(the(reagents(in(

terms(of(their(state.(

•  If(the(mass(of(a(solid(is(required(or(given,(use(

( (((((n(=((

•  If(a(solution(is(involved(use(((n(=(cV(

mM



Gases(•  If(a(gas(is(involved,(then(the(general(gas(equation(is(most(useful:(

( (PV(=(nRT((((R(=(8.31(J(KP1molP1)(

•  However,(keep(in(mind(that((((n(=(((((can(be(used(when(the(gas(is(

(((((at(STP((0°C,(1(atm(pressure)(or(

(((((at(SLC((25(°C,(1(atm(pressure)(

(((((where(VM(=(22.4LmolP1(or(24.5(L(molP1(

See(the(Exam(data(book(p5(for(these(values(

M

VV



Density(

•  Density(values(often(occur(as(part(of(a(calculation(

•  Units:(g(mLP1((or(it(could(be(g(LP1(

•  Use(the(units(to(help(you(with(density((•  eg(density(of(ethanol(is(0.785(g(mL,(so(1mL(of(ethanol(has(a(mass(of(0.785g.((

•  So(50.0(mL(of(ethanol(has(a(mass(of(((((0.785(×(50(=(39.25(g(



Sample(exam(questionsPgases(

The(reaction(that(occurs(in(an(airbag(when(an(accident(occurs(is(

10(NaN3(s)((+((2KNO3(s)((→ 5Na2O(s) + K2O(s) + 16N2(g) A particular car�s airbag was found to inflate to a volume of 62.0L at a pressure of 100kPa when the temperature reached 36.6 °C. The molar mass of NaN3 is 65.0 gmol-1. What was the mass of sodium azide contained in the car�s airbag? A. 97.9 g B. 156.6 g C. 250.6 g D. 828.1 g(



Answer(

PV(=(nRT,(so(n(=(

(

n(= ( ((((((((((=(2.41(mol((

(

From(the(equation(N2(:((NaN3(

( ((((((((((((16(:(10(

( ((((((((2.41((: ( (=(1.51(mol(

m(NaN3)(=(1.51(×(65.0(

((((((((=(97.9(g(

The(answer(is(A(

(

&

PVRT

100 62.08.31 309.6

××

102.4116

×



Sample(exam(questionsPdensity&

An(analysis(is(carried(out(on(a(sample(of(unknown(gas.(The(density(of(the(gas(is(2.86(gLP1(at(STP.(The(molecular(formula(of(the(gas(is(

A.  HCl(B.  Cl2(C.  NO2(D.  SO2(

VCAA(June(2011(Q14(



Answer:(

Density(=(2.86(gLP1(

So,(1(Litre(of(gas(has(a(mass(of(2.86(g(

At(STP,(1(mole(of(gas(occupies(22.4(L(

So,(1(mole(of(gas(has(a(mass(of((

22.4(×(2.86(=(64.06(g(=(molar(mass((

Molar(mass(of(SO2(=(32.1(+(32.0(=(64.1(

D(is(the(answer.&



The concentration of K+ ions in 100 mL of 0.0500 M K2CO3 solution, in gL-1, is

QUESTION 1


Note the careful reading required to make sure that you get the answer right here – the question is asking for gL-1 NOT molL-1

A. 0.196 B. 0.391 C. 1.96 D. 3.91



The concentration of K+ ions in 100 mL of 0.0500 M K2CO3 solution, in gL-1, is

QUESTION 1 (ANSWER)

A. 0.196 B. 0.391 C. 1.96 D. 3.91



The concentration is 3.91 gL-1 (Alternative D) Because concentration is being asked for, the volume is irrelevant. [K+] = 2 × 0.0500 molL-1 = 0.100 molL-1 Convert mol to g so m = n × M(K+) = 0.100 × 39.1 = 3.91 g




One possible reaction that occurs when trinitrotoluene (TNT), C7H5N3O6, explodes is 2 C7H5N3O6(s) � 2C(s) + 12CO(g) + 5H2(g) + 3N2(g) When one mole of TNT explodes the total volume of the gases produced from this reaction, measured at 27 °C and 1.00 × 102 kPa, is closest to

QUESTION 2

(VCAA Q5 June 2010)

A. 0.249 L B. 22.7 L C. 249 L D. 274 L



One possible reaction that occurs when trinitrotoluene (TNT), C7H5N3O6, explodes is 2 C7H5N3O6(s) � 2C(s) + 12CO(g) + 5H2(g) + 3N2(g) When one mole of TNT explodes the total volume of the gases produced from this reaction, measured at 27 °C and 1.00 × 102 kPa, is closest to

QUESTION 2 (ANSWER)

A. 0.249 L B. 22.7 L C. 249 L D. 274 L



The important term here in the question is �the total volume of the gases�. We can see from the equation that when 2 mole of TNT explodes, 20 mole of gases are produced (12CO + 5H2 + 3N2). Therefore when one mole of TNT explodes, 10 mole of gases are produced, and now we just need to convert to volume at 27 °C and 1.00 × 102 kPa. PV = nRT V= = =249.3L To 3 sig figs this answer is 249 L – alternative C

(VCAA Q5 June 2010)

nRTP

10×8.31× (27+ 273)1.00×102



A sample of the insecticide dichlorodiphenyltrichloroethane (DDT), C14H9Cl5, was found to contain 0.120 g of carbon. What mass of chlorine was present in the sample?

QUESTION 3

(VCAA Q6 June 2010)

A. 0.127 g B. 0.355 g C. 0.994 g D. 1.01 g



A sample of the insecticide dichlorodiphenyltrichloroethane (DDT), C14H9Cl5, was found to contain 0.120 g of carbon. What mass of chlorine was present in the sample?

QUESTION 3 (ANSWER)

A. 0.127 g B. 0.355 g C. 0.994 g D. 1.01 g



The answer is alternative A The formula of the compound, C14H9Cl5, gives us the molar ratio of elements in the compound. If we convert the mass of carbon into mole, we can find the amount (in mole) of chlorine and hence the mass.

n(C) = C Cl (Hydrogen can be ignored for the purposes of this question) m(Cl) =

(VCAA Q6 June 2010)

mM

0.12012

0.0114

×5



Unit 3, Area of Study 2: Organic Chemical Pathways

Alkanes and their Isomers

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CHEMISTRY



Key(Knowledge(

! structure(including(molecular,(structural(and(semiPstructural(formulae,(and(

International(Union(of(Pure(and(Applied(

Chemistry((IUPAC)(nomenclature(of(

alkanes,((alkenes,(amines,(haloalkanes,(

alkanols((CnH2n+1OH),(alkanoic(acids(

(CnH2n+1COOH)(and(esters)(up(to(C10(

&



Families(of(carbon(compounds(

! Carbon(compounds(are(classi@ied(into(homologous(series(according(to(their(structure(and(the(atoms(that(make(them(up.(

(

! An(homologous(series(can(be(described(as(a(group(of(compounds(which(have(the(same(general(formula(and(similar(chemical(properties.(



Alkanes(

•  General(formula(CnH2n+2(•  Single(bonds(occur(between(all(carbon(atoms(=(saturated(hydrocarbons(

•  Alkane(molecules(are(always(nonPpolar(•  The(systematic(names(of(all(alkanes(ends(with(–ane(



•  The(beginning((pre@ix)(of(the(name(of(any(organic(compound(indicates(the(number(of(

carbon(atoms(in(that(compound(



The&first&four&alkanes&



! As(the(size(of(the((alkane(increases,((

the(boiling(point((

increases,(due(to((

increased(strength((

of(dispersion(forces.(

! Remember&that!!only!intermolecular!forces!break!upon!!boiling.!&



Other(molecules(to(be(aware(of(! Cyclic(molecules(P(these(also(have(single(((((CPC(bonds,(BUT(they(do(not(match(the(formula,(

CnH2n+2,(their(formula(is(CnH2n((

(

(

! Benzene(is(an(arene.(It(has(the(formula(C6H6(and(is(carcinogenic.(Arenes(are(cyclic(molecules(

with(delocalised,(shared(electrons(in(a(ring.(

Naphthalene(is(also(an(arene.(

(



Isomers(

•  Structural(isomers(P(compounds(with(the(same(molecular(formula(but(different(

structures.(

•  Note(that(formulas(can(be((represented(((((in(several(

((((ways:(



Isomers(of(butane(

! The(molecular(formula(of(both(isomers(is(C4H10(! The(semi(structural(formula(of(these(molecules(would(be(

(((CH3CH2CH2CH3(and(CH3CH(CH3)CH3(



•  These(isomers(would(have(the(same(chemical(reactivity(because(they(are(both(alkanes.(

•  Their(physical(properties(differ(slightly.(•  Butane(has(a(higher(boiling(point(than(methylpropane(because(the(linear(butane(molecules(can(pack(together(more(closely(than(the(branched(methylpropane(molecules(and(stronger(dispersion(forces(can(form.(



Naming(hydrocarbons(

(

1.  Identify(longest(chain(of(Cs((⇒((main(part(of(name(

2.  Look(for(any(branches(off(the(chain(((((((branches(are(named(according(to(no.(of((Cs(eg(1(C(=(((

((((((((methyl,(2(Cs(=(ethyl)(

3.  Indicate(the(position(of(branches(by(adding(a(number,(working(from(the(end(nearest(to(the(branch((∴(lowest(number)(

4.  Numbers(are(separated(from(words(by(hyphens(and(from(each(other(by(commas.&

&



What(is(the(name(of(this(

compound?(



Sample(exam(question(–(naming(alkanes(

What(is(the(correct(systematic(name(for(the(following(compound?(

(

(

(

(

A.  2PethylP3Pmethylpentane(B.  3PmethylP4Pethylpentane(C.  3,4Pdimethylhexane(D.  2,3Pdiethylbutane(

VCAA(June(2010(Q10(




Alkenes, Haloalkanes, Amines and Alkanols

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CHEMISTRY



Key(knowledge(

•  structure(including(molecular,(structural(and(semiPstructural(formulae,(and(



(alkanes),(alkenes,(amines,(haloalkanes,(

alkanols((CnH2n+1OH),((alkanoic(acids(

(CnH2n+1COOH)(and(esters(up(to(C10)(



Alkenes(

•  Alkenes(always(have(one(CPC(double(bond.(•  The(general(formula(of(the(alkene(family(is(CnH2n(

•  They(are(more(reactive(than(alkanes(•  The(shape(around(the(C=C(bond(is(trigonal(planar,(not(tetrahedral(as(in(alkanes.(



Naming(alkenes(

•  The(ending(of(any(alkene(will(be(–ene(•  The(position(of(the(double(bond(must(be(indicated(from(C4H8(upwards.((

•  This(is(done(with(a(number(((((eg(butP1Pene,(((((((((butP2Pene(((



Functional(groups(

•  A(functional(group(is(an(atom(or(group(of(atoms(which(in@luences(the(chemical(

properties(of(an(organic(compound.(

•  You(are(required(to(name(and(draw(molecules(that(can(be(classi@ied(as(amines,(

alkanols((alcohols),(alkanoic(acids(

(carboxylic(acids),(haloalkanes(and(esters(



Amines(

•  One(H(atom(is(replaced(by(a(PNH2(group(•  General(formula(is(CnH2n+1(NH2(•  The(amine(functional(group(is(basic(–(can(gain(an(H+(ion.(

•  Amines(can(be(classi@ied(as(primary,(secondary(or(tertiary,(according(to(how(many(alkyl(chains(

are(bonded(to(the(–NH2(group.&

&



•  Amines(are(named(with(the(suf@ix(–amine(•  Eg(ethanamine(C2H5NH2(

•  Isomers(are(named(according(to(the(position(of(the(amine(group((

(((eg(butanP2Pamine(

•  Amines(are(polar(and(are(soluble(in(water(due(to(their(ability(to(form(hydrogen(bonds.(



Haloalkanes(

•  Members(of(this(homologous(series(are(alkanes(with(a(halogen((F,(Cl,(Br,(I)(atom(

replacing(one(H(atom.(

•  General(formula(CnH2n+1X(•  The(single(halogen(atom(makes(the(molecule(polar(and(makes(it(susceptible(

to(further(reactions.(



•  Naming:(Add(@luoroP,(or(chloroP(or(bromoP(or(iodoP(as(a(pre@ix(

•  Eg(chloroethane(has(the(formula(C2H5Cl(•  Isomers(are(possible:((((Isomers(of(Iodopropane(

((((((1Piodopropane(:(CH2ICH2CH3(

(2Piodopropane(:(CH3CHICH3(

(((((Numbers(are(used(to(indicate(the(position(((

(((((of(the(halogen(atom,(directly(in(front(of((

(((((the(pre@ix.(



Alkanols((alcohols)(

•  One(H(is(replaced(by(–OH(•  General(formula(CnH2n+1OH(•  The(name(of(an(alcohol(always(ends(in(–ol(•  Eg(ethanol(C2H5OH(•  The(functional(group((POH)(is(called(a(hydroxyl(group(



•  Isomers(are(named(according(to(the(position(of(the(POH(group(

(

•  Eg(butanP1Pol(:(CH3CH2CH2CH2OH(and(butanP2Pol:(CH3CH2CH(OH)CH3(

•  The(presence(of(the(hydroxyl((POH)(group(makes(the(molecule(polar(and(also(able(to(

hydrogen(bond(with(water(molecules((

(∴(small(alcohols(can(dissolve(in(water.(



Sample(exam(questions(–(

functional(groups(and(isomers(For(which(one(of(the(following(molecular(formulae(is(there(only(one(possible(structure?(

A.  C2HCl3(B.  C2H4Cl2(C.  C2H2Cl2(D.  C4H9OH(

(

VCAA(June(2010(Q11(



How(many(structural(isomers,(each(containing(a(double(bond,(have(the(molecular(formula(C5H10?(

A.  3(B.  4(C.  5(D.  6(

(

VCAA(June(2008(Q16(




Alkanoic Acids and Esthers

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CHEMISTRY



Key(knowledge(

•  structure(including(molecular,(structural(and(semiPstructural(formulae,(and(



(alkanes,(alkenes,(amines,(haloalkanes,(

alkanols((CnH2n+1OH),)(alkanoic(acids(

(CnH2n+1COOH)(and(esters(up(to(C10(



Alkanoic((Carboxylic)(acids(

•  One((H(is(replaced(by(PCOOH((

(

(

•  Only(the(end(carbon(can(have(this(functional(group(on(it,(so(few(structural(isomers(can(occur,(although(don’t(forget(branched(structures.(

•  The(functional(group(is(called(a(carboxyl(group(



•  General(formula(is(RCOOH(where(R(is(an(alkyl(group((methyl,(ethyl,(propyl(etc)(

•  The(name(of(a(carboxylic(acid(always(ends(in(((((((–oic(acid.(

•  The(total(number(of(Carbons(in(the(compound(gives(us(the(name(so(C3H7COOH(with(4(Cs(is(butanoic(acid.(

(

(

(

•  These(compounds(are(acidic,(the(H(of(the(((PCOOH(group(can(be(donated(in(an(acid(base(reaction.(

•  Alkanoic(acids(are(the(most(common(weak(acids(that(you(will(encounter.(



•  Carboxylic(acids(are(polar(molecules(with(high(melting(points(

•  The((formation(of(hydrogen(bonds(between(carboxylic(acids(creates(dimers((so(their(melting(

point(becomes(effectively(equal(to(that(of(a(

molecule(with(double(the(molar(mass).((

•  Hydrogen(bonding(with(water(makes(them(soluble(in(water(



Esters(•  Esters(have(a(functional(group(with(the(formula(–COPOP(

•  The(ending(–oate(indicates(((((an(ester(functional(group.(

•  Esters(are(formed(when(((((alkanols(react(with(alkanoic(acids,(so(their(names(((

((((are(formed(from(these(two(compounds,(the(alkanol((

((((name(is(@irst(and(is(reduced(to(�alkyl�(eg(if(the((((

(((((alkanol(was(ethanol,(then(the(ester(name(would((

(((((start(with(ethyl.(

•  An(ester(that(is(formed(from(propanol(and(ethanoic(acid(is(called(propyl(ethanoate(



Naming(esters(from(their(

structures(•  When(trying(to(name(an(ester(from(its(structure,(you(need(to(locate(the(functional(group(@irst.(

(

(

•  The(alkyl(chain(which(included(the(C=O((carbonyl(group)(has(come(from(the(carboxylic(acid,(and(the(alkyl(chain(nearest(the(–OP(has(come(from(the(alkanol.(

•  Name(the(ester(with(the(alkanol(@irst:(this(one(is(ethyl(ethanoate.(



Amides(

•  Although(this(functional(group(is(not(on(the(key(knowledge(list,(it(occurs(in(proteins(and(is(often(

used(in(past(exam(questions.(

•  The(amide(functional(group(can(appear(((((((as ( ( ( (or(

(

(

depending(on(whether(it(is(on(the(end(or(in(the(

middle(of(a(compound(



Sample&exam&quesFons&–&alkanoic&acids,&esters&and&amides&

The(structure(of(tami@lu®,((

an(anti@lu(drug(is(shown((

opposite.(

The(names(of(the(

functional(groups(

labelled(I,(II(and(III(are(I& II& III&

A.( Amide( Amino( Carboxylic(acid(

B.( Amino( Amide( ester(

C.( Amide( Amino( ester(

D.( Amino( Amide( Carboxylic(acid(

VCAA(June(

2010(Q19(



The(number(of(structural(isomers(that(

are(carboxylic(acids(with(the(formula(

C4H8O2(is(

A.  1(B.  2(C.  3(D.  4((

VCAA(June(2006(Q9(

&




Substitution Reactions of Alkanes and

Addition Reactions of Alkenes

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CHEMISTRY



Key&knowledge&

•  common(reactions(of(organic(compounds(including(equations:(addition(reactions(of(

alkenes((addition(of(hydrogen(halides(and(

water(limited(to(symmetrical(alkenes),(

substitution(reactions(of(alkanes(



&Combustion(reactions(

! Most(hydrocarbons(will(undergo(combustion(in(the(presence(of(oxygen.(

! There(are(two(types(of(combustion(reactions(–(complete(combustion(and(incomplete(

combustion.(

! The(products(of(complete(combustion(are(CO2(and(H2O,(while(incomplete(combustion(may(

form(CO(and/or(C(and(H2O(

! Eg(CH4(g)(+(2O2(g)(→(CO2(g)(+(2H2O(l)(((((2CH4(g)(+(3O2(g)(→(2CO(g)(+(4H2O(l)(



Substitution(reactions(of(alkanes(

•  In(a(substitution(reaction,(one(or(more(of(the(hydrogen(atoms(on(the(alkane(is(replaced(by(

another(atom(or(functional(group.(

•  Heat(or(UV(light(is(needed(to(start(a(substitution(reaction(when(the(bond(in(the(halogen(molecule(is(

broken(and(two(free(radicals(are(formed.(

•  Haloalkanes(are(made(when(alkanes(react(with(halogens(such(as(chlorine(and(bromine(in(this(way.(



Formation(of(a(haloalkane(

! Alkane(+(halogen(→(haloalkane(+(hydrogen(halide((

eg(CH4((+((Cl2((((((((((((((((((((((((CH3Cl((+((HCl(

(

! After(the(substitution(of(one(chlorine(onto(the(alkane,(another(can(be(substituted:(

(CH3Cl((+((Cl2((→((CH2Cl2((+((HCl(

!  If(enough(chlorine(is(present,(this(can(continue(right(up(to(CCl4(

! This(applies(to(other(halogens(reacting(in(the(same(way.(

UV light!!!!→



Addition(reactions(of(Alkenes(

! The(CPC(double(bond,(is(more(reactive(than(the(CPC(single(bond(so(alkenes(are(more(reactive(than(alkanes.((

! Addition(reactions(involve(the(CPC(double(bond(becoming(a(single(bond((‘breaking’)(and(extra(atoms(or(functional(groups(‘adding’(onto(the(molecule.(

! The(new(atoms(or(functional(groups(always(add(‘across’(the(double(bond(–(with(one(atom((or(functional(group)(on(each(side(of(what(used(to(be(the(double(bond.(



Some(typical(addition(reactions(

(all(follow(the(same(pattern)(1.  Reaction(with(a(halogen(2.  Reaction(with(hydrogen((hydrogenation)(3.  Reaction(with(a(hydrogen(halide(4.  Reaction(with(water((steam)(5.  Addition(polymerisation(



1.(Reaction(with(a(halogen(

•  Alkene(+(bromine((→((dibromoalkane(

•  Eg(CH2=CH2((+((((((Br2((((((→((CH2BrCH2Br(

((((((colourless((redPbrown(colourless(

•  This(reaction(is(used(to(identify(the(presence(of(unsaturation((double(bonds)(in(a(hydrocarbon.(

•  The(redPbrown(colour(of(bromine(disappears(when(it(reacts(with(an(alkene,(but(not(with(an(alkane((unless(UV(light(is(present).(



•  An(alkane(will(not(react(with(bromine(unless(UV(light(is(present,(whereas(an(

alkene(will(instantly(react(with(bromine(and(

the(brown(colour(disappears.(



2.(Reaction(with(hydrogen(

! This(is(used(to(decrease(the(number(of(double(bonds(in(an(unsaturated(hydrocarbon(–(in(

particular(in(making(margarine.(

! Alkene(+(hydrogen(((→(((alkane(

(

! Eg(CH2=CH2(+(H2((→((CH3CH3(

→ +



3.(Reaction(with(a(hydrogen(halide(

•  While(the(reaction(with(a(halogen(produces(a(dihaloalkane,(this(reaction(adds(just(one(halogen(

atom(onto(the(alkane,(making(a(haloalkane.(

•  Only(symmetrical(alkenes((with(the(double(bond(exactly(in(the(middle(of(the(molecule)(need(to(be(

used(as(examples(

•  Alkene(+(hydrogen(chloride(→(chloroalkane(



examples&

•  CH2=CH2(+(HCl(→(CH3CH2Cl(

•  CH3CH=CHCH3+(HBr(→CH3CH2CH2BrCH3(



4.(Reaction(with(water(

•  This(is(an(easy(method(for(making(an(alkanol(•  A(catalyst(is(used(–(phosphoric(acid(•  Alkene(+(steam(→(alcohol(

( ( ( ( (((((((H3PO4(

•  Eg(CH2=CH2(g)(+(H2O(g)(((→(((CH3CH2OH(l)(

•  (catalyst(is(always(written(over(the(arrow)&•  Only(symmetrical(alkenes(need(to(be(used(

+ →



Sample(exam(questionP(

substitution(and(addition(reactions(A(student(was(given(four(colourless(liquids(that(were(labelled(A,(B,(C(and(D.(They(were(known(to(be(ethanol,(

ethanoic(acid,(pentane(and(hexene,(but(the(exact(identity(

of(each(liquid(was(unknown.(The(student(tested(the(

properties(of(each(liquid(and(obtained(the(results(shown(

below.(

( A& B& C& D&

Solubility(in(water(

insoluble( soluble( soluble( insoluble(

Addition(of(Br2(solution(

Colour(disappears(

No(immediate(

reaction(

No(immediate(

reaction(

No(immediate(

reaction(

Addition(of(Na2CO3(powder(

No(reaction( Gas(evolved( No(reaction( No(reaction(

VCAA(June(2006(Q1(




Substitution Reactions of Haloalkanes,

Oxidation of Alkanols and Esterification Reactions

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CHEMISTRY



Key&knowledge&

•  common(reactions(of(organic(compounds(including(equations:(substitution(reactions(

of(primary(haloalkanes,(oxidation(of(

primary(alkanols,(and(esteri@ication)(



Primary&haloalkanes&

•  Haloalkanes(are(named(according(to(the(number(of(carbon(atoms(that(are(bonded(to(the(carbon(on(

which(the(halogen(is(bonded.(

•  A(primary(haloalkane(has(the(halogen(atom(bonded(to(a(carbon(that(is(on(the(end(of(the(

carbon(chain(–(it(is(only(bonded(to(one(other(

carbon((hence(‘primary’)(

•  eg((CH3CH2CH2Cl(



Substitution(reactions(of(haloalkanes(

•  In(this(case(the(substitution(reaction(involves(the(replacement(of(one(functional(group(with(

another.(

•  The(halogen(atom(makes(the(carbon(atom(into(a(positive(charge(centre,(so(nucleophiles(

(functional(groups(with(a(nonPbonding(pair(

of(electrons(or(a(negative(charge)(are(

attracted(to(it.(

•  Hydroxide(ions,(water((and(ammonia(are(all(nucleophiles(



Equations:(

CH3Cl(+(OHP((→(CH3OH(+(Cl

P(

C2H5Cl(+(H2O(→(C2H5OH(+(HCl(



Oxidation(reactions(of(alkanols(

•  Oxidation(of(a(primary(alkanol(produces(a(carboxylic(acid(

•  NB(The(oxidant(used(is(either(the(permanganate(ion,(or(the(dichromate(ion.(In(addition,(heat(is(required(and(acid((eg(H2SO4)(

•  This(is(how(vinegar(is(made(from(wine!(•  When(wine(�goes�(off,(we(often(say(it(has(gone(�vinegary�(–(because(ethanoic(acid(has(been(made(by(the(oxidation(of(the(ethanol(by(oxygen(in(the(air((and(bacteria)(



•  Only(primary(alkanols(produce(carboxylic(acids(when(oxidised:(

•  Secondary(alkanols(oxidise(to(ketones(and(tertiary(alkanols(cannot(be(oxidised.(



Alkanoic(acids(as(weak(acids(

•  Alkanoic&acids&ionise&to&a&limited&extent&in&water,&producing&a&weakly&acidic&soluFon.&

&

•  Watch&for&opportuniFes&in&which&acidBbase&reacFons&may&occur&between&an&alkanoic&acid&and&a&base,&such&as&sodium&hydroxide.&

&



Esteri@ication(reactions(•  Esteri@ication(is(a(condensation(reaction(in(which(an(ester(is(produced(

•  The(reaction(occurs(between(an(alkanoic(acid(and(an(alkanol.(

•  (Alkanol(+(alkanoic(acid((→(ester(+(water(

•  An(acid(catalyst(–(eg(H2SO4(is(required(for(this(reaction(to(work(and(the(mixture(must(be(

heated(



•  The(name(of(an(ester(is(taken(from(the(names(of(the(alcohol(and(carboxylic(acid(from(which(it(

is(formed.(

•  The(name(of(an(ester(ends(in((Poate((eg(the(ester(made(from(ethanol(and(propanoic(

acid(would(be(ethyl(propanoate((note(the(

alcohol(name(comes(@irst)(

From the carboxylic acid From the

alcohol



Properties(of(esters(

•  Many(esters(have(a(strong(smell(or(@lavour.(•  Many(arti@icial(@lavourings((eg(banana(essence)(are(esters.(

•  Small(molecular(esters(are(volatile((become(vapour(easily)(and(are(smelly.(

•  Large(molecular(esters(include(waxes(and(oils(



General(equation(for(esteri@ication(



Equations(for(the(formation(of(esters(

Ethanoic acid ethanol ethyl ethanoate water

CH3COOH((((((+(((((C2H5OH(( ( (((((CH3COOC2H5((((+(((((((H2O(((

1.(Ethyl(ethanoate(



2.  Hexyl(propanoate(Hexanol(+(propanoic(acid ((((((((hexyl(propanoate(+(water(

(

C6H13OH((+((C2H5COOH( ((((((C2H5COOC6H13((+(H2O(

&&&



Sample(exam(question(–(substitution,(oxidation(and(esteri@ication(

Which(one(of((

the(following((

organic(reactions((

does(not(result(in((

the(product((

shown(on(the((

rightPhand(side((

of(the(reaction?(



Answer(•  Alternative(A(is(a(substitution(reaction(between(sodium(hydroxide(and(1Pchlorobutane(to(make(butanP1Pol.(

•  Alternative(B(is(an(addition(reaction(between(butP2Pene(and(HCl(which(should(make(2Pchlorobutane,(however(the(product(given(is(1Pchlorobutane(which(is(impossible.(

•  Alternative(C(is(an(esteri@ication(reaction(between(methanol(and(ethanoic(acid(forming(methyl(ethanoate(

•  Alternative(D(is(an(addition(reaction(between(propene(and(steam(forming(propanP2Pol(

(




Reaction Pathways

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CHEMISTRY



Key(knowledge(

•  common(reactions(of(organic(compounds(including(equations:(addition(reactions(of(

alkenes((addition(of(hydrogen(halides(and(water(

limited(to(symmetrical(alkenes),(substitution(

reactions(of(alkanes(and(primary(haloalkanes,(

oxidation(of(primary(alkanols,(and(esteri@ication(

•  organic(reaction(pathways(including(appropriate(equations(and(reagents:((

–(production(of(esters(from(alkenes(



Reaction(Pathways((

In(the(previous(sections(we(have(found(a(range(of(

ways(to(produce(certain(chemicals.(

eg(Ethanol(can(be(produced(by((

1.  the(addition(reaction(between(ethene(and(steam((

2.  the(substitution(reaction(between(chloroethane(and(sodium(hydroxide(

&



•  These(different(methods,(sometimes(with(many(stages,(are(known(as(reaction(pathways.(

•  It(is(important(to(be(aware(of(the(principles(of(green(chemistry(including(the(minimisation(of(

waste(materials,(of(energy(use(and(the(use(of(

environmentally(friendly(solvents.(



•  Reaction(pathways(can(be(represented(visually(as(a(web(of(reactions.((



The(synthesis(of(ethyl(propanoate(

•  Ethyl(propanoate(is(an(ester(which(is(made(from(ethanol(and(propanoic(acid(

•  Ethanol(can(be(made(by(two(different(reaction(pathways(



Similarly(propanoic(acid(can(be(made(by(a(reaction(pathway(from(propane(



&The(two(pathways(join(to(make(ethyl(

propanoate&&



Sample(exam(question(–(reaction(

pathways(The(ester(methyl(propanoate(has(a(characteristic(fruity(odour(and(has(been(isolated(from(many(fruits(including(pineapple.(A(sample(of(this(ester(is(to(be(prepared(in(the(laboratory.(A(partly(completed(reaction(pathway(for(this(preparation(is(shown(below.(

C3H7Cl(

((((((((reagent(X(

(

(

(

Compound(K ( ((((((((C3H6O2 ( (((((((methyl ( ( ( ( (( ((((((((( ( ( ( ( ( ( ((((((((((((((propanoate(

(

( (((((((((((compound(L(((

2-2 7

+Cr Oand H!!!→

2 4

concentratedH SO catalyst!!!!!→



(i)  Write(a(structural(formula,(showing(all(bonds,(for(methyl(propanoate(

(ii) Write(structural(formulae,(showing(all(bonds,(for(compounds(K(and(L(

(iii) Write(the(formula(of(reagent(X((

(

VCAA(June(2008(Q6(




Proteins: Formation and Structure

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CHEMISTRY



Key(Knowledge(•  organic(reaction(pathways(including(appropriate(equations(and(reagents:(

((((P(condensation(and(polymerisation(reactions((((

(((((((that(produce(large(biomolecules(including(((

((((((((carbohydrates),(proteins((and(DNA)(

•  chemical(bonding:(–(primary,(secondary(and(tertiary(structures(of(proteins(

–(the(role(of(the(tertiary(structure(of(proteins(in(enzyme(

action(

–(denaturing(of(proteins:(effect(of(changes(in(pH(and(

temperature(on(bonding(



Proteins&

•  Proteins(are(fundamental(to(the(structure(of(cells(as(well(as(their(operation.(

•  They(may(be(structural,(such(as(proteins(in(muscle,(hair,(nails(etc(

•  Enzymes(are(proteins(which(catalyze(many(reactions(that(occur(in(the(human(body.(

•  Hormones(are(proteins,(as(is(haemoglobin(which(carries(oxygen(around(in(the(blood.(



Amino(acids(

•  The(monomers(from(which(proteins(are(built(are(called(2Pamino(acids((or(αPamino(acids).(

•  They(consist(of(a(central(C(atom(which(has(bonded(to(it(a(carboxyl((COOH)(group(and(

an(amine((NH2)(group(as(well(as(a(H(atom(

and(a(side(chain(denoted(((

(((as(–Z(which(may(be(one(of(20(

(((different(groups.((



The&side&chains&The(20(different(side(chains(are(shown(in(the(data(

book((table(8)(

(



The(functional(groups(•  The(carboxyl(group(allows(an(amino(acid(to(behave(in(solution(as(an(acid.(

•  When(the(pH(is(high,(the(amino(acid(donates(an(H+(ion(to(the(solution(and(it(becomes(negatively(charged.(

•  The(amine(group(allows(an(((((amino(acid(to(behave(as(a((

((((base(in(solution.(

•  When(the(pH(is(low,(the((((((amino(acid(can(accept(an((

((((H+(ion(from(the(solution((

((((and(it(becomes(positively((

(((charged.(



•  In(an(approximately(neutral(solution,(an(amino(acid(will(have(both(gained(and(lost(an(H+,(so(will(

have(a(positive(and(a(negative(charge.(

•  This(is(called(a(‘Zwitterion’.(•  The(pH(at(which(the(amino(acid(exists(as(a(zwitterion(is(called(its(isoelectric(point(and(

depends(on(the(side(chain(of(the(amino(acid.(

&



Formation(of(proteins(

•  Amino(acids(undergo(condensation(reactions(with(other(amino(acids(to(form(dipeptides,(

polypeptides(and(proteins.(

(((An(amide(functional(group(joins(the(residues(of(

the(alkanoic(acid(and(amine.(

((((This(functional(group(may(also(be(called(a(

peptide(link.(



Forming(a(dipeptide(

A(condensation(reaction(causes(a(molecule(of(water(to(be(formed(each(time(two(amino(acids(join(via(an(

amide(functional(group(or(peptide(link.(



Structure(of(proteins(

•  The(structure(of(proteins(is(very(involved(and(may(be(described(at(different(levels(of(complexity.(

•  These(levels(are(known(as(the(primary,(secondary,(tertiary(and(quaternary(structures(of(a(protein.(



Primary(structure(

•  This(is(the(type,(number(and(the(sequence(of(amino(acids(in(a(protein(chain.(

•  The(bonding(involved(here(is(covalent(bonding.(



Secondary(structure(

•  A(protein(chain(is(very(long((more(than(50(amino(acids)(and(coils(up(due(to(hydrogen(

bonds(between(different(parts(of(the(chain.(

•  The(chain(may(form(a(spiral((αPhelix)(or(a(pleated(sheet((like(corrugated(cardboard)(



Tertiary(structure(

•  The(coiled(protein(chain(is(still(long(and(folds(up(to(form(the(operational(shape(of(the(protein.((

•  This(is(the(tertiary(structure.(•  Bonds(form(between(ZPgroups(of(the(amino(acids.(These(may(be(dispersion(forces,(hydrogen(bonds,(

ionic(bonds,(or(even(covalent((disul@ide(bridge)(

bonds.(



•  This(overall(threePdimensional(shape(helps(to(determine(the(function(of(a(protein.(

•  Many(proteins(have(a(metal(ion(as(part(of(their(structure,(or(may(be(made(up(of(several(protein(

chains(bound(together.(

•  This(fully(working(shape(of(the(protein(is(its(quaternary(structure.(



Sample(exam(question(P(proteins(

The(following(structure(shows(part(of(a(polypeptide(

(

(

(

(

(i)  Name(the(amino(acids(that(make(up(this(section(of(the(polypeptide(

At(a(particular(pH,(an(amino(acid(in(solution(can(exist(as(ions(that(have(both(a(negative(and(positive(charge.(These(ions(are(called(zwitterions.(

((ii)((Choose(one(of(the(amino(acids(in(this(section(of((((

((((((((((polypeptide(and(draw(the(structure(of(its((

((((((((((zwitterion(clearly(showing(all(bonds.(

(



Answer(

(i)(

(

(

(

(

(

(

(

(ii)((Zwitterion:(




Proteins: Tertiary Structure and Enzymes

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CHEMISTRY



Key(Knowledge(

•  chemical(bonding:(–(primary,(secondary(and(tertiary(

structures(of(proteins(

–(the(role(of(the(tertiary(structure(of(

proteins(in(enzyme(action(

–(denaturing(of(proteins:(effect(of(changes(

in(pH(and(temperature(on(bonding(

&



The&four&levels&of&protein&structure&



Enzymes(•  Enzymes(are(proteins(that(act(as(biological(catalysts((increase(the(rate(of((biological(reactions).(

•  An(example(of(a(most(ef@icient(enzyme(is(catalase.((

•  Each(catalase(molecule(can(decompose(millions(of(hydrogen(peroxide(molecules(every(second(

((((((((((((((((((2H2O2((→ (2H2O((+((O2((



The&catalase&enzyme&



•  Compared(to(inorganic(catalysts,(enzymes(are:(

– More(ef@icient(–(resulting(in(much(faster(reactions(

– More(speci@ic(–(may(only(work(for(one(reaction(

– Able(to(act(only(in(a(narrow(temperature(range(–(body(temperature(

– Able(to(act(only(in(a(narrow(pH(range(



Enzyme(action(

•  The(tertiary(structure(of(the(enzyme(enables(it(to(form(intermolecular(bonds(with(speci@ic(

reactants((the(substrate)(and(so(determines(

the(catalytic(ability(of(an(enzyme.(

•  The(enzyme(has(an(active(site(which(is(where(the(substrate((reactants)(binds(by(

intermolecular(bonding.(

•  The(active(site(@its(the(required(molecules(exactly(and(this(is(where(the(reaction(occurs.(



•  When(the(products(are(released(from(the(active(site,(the(enzyme(is(able(to(accept(

another(substrate(and(so(on.(

•  It(is(not(changed(by(the(reaction(it(is(catalysing.(

•  Enzymes(are(thought(to(act(according(to(the(lock(and(key(mechanism.(

•  This(describes(the(enzyme’s(active(site(as(@itting(the(substrate(perfectly.(



The(lock(and(key(mechanism(of(enzyme(

action(



Denaturation(of(enzymes(

•  When(enzymes(are(heated(to(a(temperature(above(their(normal(

operation(temperature,(or(when(the(pH(of(

the(solution(is(changed,(their(structure(is(

disrupted,(intermolecular(bonds(are(

broken(and(the(enzyme(is(denatured.(



•  After(denaturation,(the(protein(chains(may(come(together(again,(but(

the(working(shape(has(been(lost(and(

the(chains(just(clump.((

•  This(is(coagulation.(



•  Examples(of(coagulation(–(cooking(eggs:(clear(egg(white(becomes(hard(and(white(

(P(cooking(meat(–(becomes(brown(and(

harder(

(P(Curdling(milk(with(lemon(juice(or(

vinegar.(

&



•  Below(normal(operating(temperatures,(enzymes(become(inactive.((

•  They(may(work(very(slowly(or(not(at(all.((•  If(the(temperature(increases(again,(their(structure(is(still(intact.(

•  SO,(in(summary,(denaturation(stops(the(enzyme(from(working(altogether(because(

the(tertiary(structure(is(changed,(while(

deactivating(slows(it(right(down,(but(the(

enzyme(can(become(active(again.(



Sample(exam(question(P(enzymes(Which(one(of(the(following(statements(about(enzymes(is(not(true?(

A.  Enzymes(can(only(be(denatured(by(an(increase(in(temperature(

B.  Enzymes(may(form(temporary(ionPdipole(bonds(with(substrate(molecules(

C.  Enzymes(speed(up(reactions(by(holding(substrate(molecules(in(positions(necessary(for(reaction.(

D.  The(tertiary(structure(of(an(enzyme(may(be(altered(if(one(amino(acid(in(its(primary(structure(is(substituted(for(another,(different((amino(acid.(

VCAA(June(2009(Q(17(



Answer(A.  Is(not(true,(as(a(change(in(pH(also(causes(

enzymes(to(be(denatured.(

B.  Is(true,(as(ionPdipole(bonds(may(indeed(be(formed(between(substrates(and(enzymes(

C.  Is(true.(This(is(the(method(by(which(enzymes(work.(

D.  Is(true,(since(a(change(in(the(primary(structure(may(indeed(have(an(effect(on(the(

tertiary(structure.(

A(is(the(answer!(




Lipids

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CHEMISTRY



Key(Knowledge(

organic(reaction(pathways(including(

appropriate(equations(and(reagents:(

–(condensation(reactions(that(produce(lipids(

(limited(to(triglycerides)(



Lipids(

•  Lipids(are(a(class(of(molecules(that(include(fats,(oils,(steroids((including(cholesterol)(

and(waxes.(

•  Fats(and(oils(are(triglycerides.(•  Each(triglyceride(molecule(is(formed(by(the(condensation(reaction(between(one(

glycerol(molecule(and(three(fatty(acids.((



FormaFon&of&a&triglyceride&

•  Fatty(acids(are(carboxylic(acids(with(a(long(hydrocarbon(chain(eg(H3C(CH2)16COOH(



•  The(difference(between(fats(and(oils(is(that(fats(are(solid(at(room(temperature(

whereas(oils(are(liquid.(

•  Fats(tend(to(come(from(animal(sources(whereas(oils(tend(to(come(from(plants.(

•  There(are(other(lipids(such(as(phospholipids((used(to(make(the(

membrane(of(cells)(and(steroids(

(including(cholesterol),(but(in(this(course(

we(will(only(discuss(triglycerides.(



Types(of(fats(

•  A(fat((or(oil)(is(named(according(to(the(type(of(fatty(acids(in(it.(

•  Saturated(fats(are(made(from(fatty(acids(with(only(carbonPcarbon(single(bonds.(

•  They(are(generally(considered(to(be(unhealthy.(

•  They((saturated(fatty(acids)(have(the(general(formula(CnH2nO2(



Unsaturated(fats(•  A(monoPunsaturated(fat(is(made(from(fatty(acids(with(only(one(carbonPcarbon(double(bond(per(fatty(

acid.(

•  General(formula(CnH2nP2O2(•  The(reduced(number(of(hydrogens(is(due(to(the(presence(of(the(double(bond.(

•  PolyPunsaturated(fats(are(found(in(vegetable(oils.(•  They(have(more(than(one(carbonPcarbon(double(bond(per(fatty(acid.(

•  General(formula(may(be(one(of(((CnH2nP4O2((two(double(bonds)((

or(CnH2nP6O2((three(double(bonds)((etc(

&



&

&Type&of&

fat&

Name&of&

fatty&acid&

Semi.structural&formula& Molecular&

formula&

saturated( Stearic( CH3(CH2)16COOH( C18H36O2(MonoP

unsaturated(Oleic( CH3(CH2)7CH=CH(CH2)7COOH( C18H34O2(

PolyP(

unsaturated(Linoleic( CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH( C18H32O2(

PolyP(

unsaturated(Linolenic( CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH(

(C18H30O2(

(



Table(9(from(the(data(book(



Melting(point(of(triglycerides(

•  The(presence(of(CPC(double(bonds(in(the(fatty(acid(chains(creates(‘kinks’(in(the(chain.(

•  This(prevents(them(from(packing(closely(and(reduces(the(strength(of(the(dispersion(forces(between(the(chains.(

•  This(lowers(the(melting(point(of(the(unsaturated(fat.(

•  So(unsaturated(fats,(with(double(bonds((and(kinks)(are(liquids(and(have(lower(melting(points(than(saturated(fats((solids)(with(only(single(bonds(with(only(single(CPC(bonds.(

&



Digestion(of(triglycerides(

•  Fats(are(emulsi@ied(by(bile(in(the(small(intestine,(then(enzymes(catalyse(the(alkaline(hydrolysis(of(the(ester(linkages(to(form(fatty(acids(and(glycerol.(

•  These(small(molecules(are(absorbed(into(the(blood(stream(and(are(reassembled(into(triglycerides(which(are(transported(in(lipoproteins(to(adipose(tissue(where(the(fats(are(stored.(



Condensation(Polymerisation(–(a(

summary(

•  If(a(monomer(has(a(functional(group(on(each(end,(it(can(react(with(other(monomers(in(a(

series(of(condensation(reactions(to(form(a(

condensation(polymer.(

•  Condensation(polymers(occur(in(biomolecules(as(well(as(synthetic(@ibres(

such(as(nylon(and(polyesters.(



Functional(groups(and(their(

polymers(Polymer& Functional&

group&

Other&name& Formed&from&

these&

functional&

groups&

Proteins(

(dipeptides(and(

polypeptides)(

Nylon(

Amide( Peptide(linkage( Amino(and(

carboxyl((

Carbohydrate( Ether( Glycosidic(

linkage(

Two(hydroxyl(

Triglyceride((not(

really(a(polymer)(

Polyester(

Ester( Carboxyl(and(

hydroxyl(



Sample(exam(question(P(triglycerides(

(a)((i)(A(long(chain(carboxylic(acid(can(be(represented(by(the(general(formula(RCOOH(where(R(represents(a(

hydrocarbon(group.(Draw(the(structure(of(a(fat(formed(by(

the(reaction(between(glycerol(and(three(molecules(of(

RCOOH.(Clearly(show(the(structure(of(all(ester(groups(in(

the(fat.(



(ii)(Palmitic(acid((C16H32O2)(and(oleic(acid((C18H34O2)(are(both(long(chain(carboxylic(acids.(Which(one(of(them(is(classi@ied(as(an(unsaturated(carboxylic(acid?(

Answer:(

General(formula:(CnH2nO2(

(

(

(

(

(b) Unsaturated(fats(can(be(converted(into(saturated(fats(by(reaction(with(hydrogen(gas(in(the(presence(of(a(metallic(catalyst.(In(one(such(conversion,(2.50(mole(of(an(unsaturated(fat(is(converted(to(a(saturated(fat(by(reaction(with(15.0(g(of(H2(gas.(Calculate(the(number(of(carbon(to(carbon(double(bonds(present(in(a(molecule(of(the(unsaturated(fat.(

(

VCAA(Nov(2006(Q9(



Answer((b)(

n(H2)(=(

(

n(fat)(=(2.50(mol(

1(mol(of(H2(reacts(with(1(mol(of(double(

bonds(

So(n(double(bonds)(=(

(

There(are(3(double(bonds(in(each(molecule(

of(the(unsaturated(fat.((

15.07.50mol

2.02=

7.503 mol

2.50=




Carbohydrates

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/unit-3-area-study-2/organic-chemical-pathways-carbohydrates/key-knowledge/

CHEMISTRY



Key(Knowledge(

•  organic(reaction(pathways(including(appropriate(equations(and(reagents:(

–(condensation(and(polymerisation(reactions(

that(produce(large(biomolecules(including(

carbohydrates,((proteins(and(DNA)(



Carbohydrates(

•  Carbohydrates(are(our(primary(energy(source.(

•  They(include(monosaccharides(such(as(glucose,(disaccharides(such(as(sucrose,(and(

polysaccharides(such(as(starch(and(

cellulose.(



Monosaccharides(

•  All(have(the(general(formula(CH2O(•  They(are(the(simplest(sugars(•  Glucose(has(the(formula(C6H12O6(and(can(occur(in(solution(as(one(of(two(cyclic(

molecules((α(and(β(glucose)(or(a(straight(chain(version.(

•  This(is(α(glucose:(&&&&



•  Fructose(and(galactose(are(also(common(monosaccharides.(

•  Fructose:(

•  All(are(very(soluble(in(water(due(to(the(presence(of(a(large(number(of(hydroxyl(groups(and(the(consequent(hydrogen(bonding(that(is(possible(between(the(hydroxyl(groups(and(the(water(molecules.(



Disaccharides(

•  A(condensation(reaction(between(hydroxyl(groups(on(adjacent(monosaccharides(will(

result(in(a(disaccharide.(

•  Maltose(is(formed(when(two(glucose(molecules(join(in(a(condensation(reaction(

with(a(water(molecule(being(released.(

&&



•  Glucose(+(galactose(→(lactose(

•  Glucose(+(fructose(→(sucrose(

•  The(monomers(are(joined(by(a(glycosidic(linkage,(also(known(as(an(ether(functional(

group.(

&



Polysaccharides(

! There(are(three(different(types(of(polysaccharides(that(can(be(formed(from(

glucose(

◦  Starch(" The(molecule(that(plants(use(to(store(energy(◦  Cellulose(" A(structural(molecule(used(in(plant(cell(walls((" Cannot(be(digested(by(humans((dietary(@ibre)(◦  Glycogen(" The(molecule(that(animals(use(to(store(energy.(



Starch(•  This(is(made(up(of(long(chains(of(αPglucose.(•  There(is(little(branching(in(starch(making(it(slow(to(be(hydrolysed((broken(down(into(glucose(

molecules)(/(digested(by(enzymes(in(presence(of(

water.((



Cellulose(

•  Cellulose(is(a(linear(polymer(of(αPglucose(and(βPglucose.(

•  Individual(bundles(of(cellulose(molecules(are(joined(by(hydrogen(bonds(



Glycogen(

•  This(is(a(branched(polymer(of(αPglucose.(•  The(branches(make(it(easier(for(enzymes(to(hydrolyse(the(ether(linkages(and(

release(the(glucose(for(respiration((and(

the(production(of(energy).(

&



Sample(exam(question(P(carbohydrates(

Amylase(is(an(enzyme(that(speci@ically(digests(

starch(in(humans.(A(major(product(of(this(starch(

hydrolysis(reaction(is(

A.  Maltose(B.  Glycogen(C.  Cellulose(D.  Glycerol((

VCAA(June(2006(Q(14(



Answer(

•  Starch(is(a(condensation(polymer(of(glucose(((((When(it(is(hydrolysed,(it(breaks(down(into(((

(((((smaller(molecules,(such(as(the(disaccharide,(((

(((((maltose.(

•  Glycogen(and(cellulose(are(both(also(condensation(polymers(of(glucose,(but(one(polymer(will(not(be(hydrolysed(to(make(a(different(polymer.(

•  Glycerol(is(a(small(molecule(that(is(produced(when(fats(are(hydrolysed.(

•  The(answer(is(A.((




DNA

Watch this lesson online: https://edrolo.com.au/vce/subjects/chemistry/vce-chemistry/unit-3-area-study-2/organic-chemical-pathways-dna/key-knowledge/

CHEMISTRY



Key&Knowledge&

! chemical(bonding:(–(primary(and(secondary(structure(of(DNA(

! organic(reaction(pathways(including(appropriate(equations(and(reagents:(

–(condensation(and(polymerisation((

((((reactions(that(produce(large(biomolecules((

(((((including((carbohydrates,(proteins(and)((((

(((((DNA(



Biological(Importance(of(DNA(

•  Chromosomes(are(found(in(the(nucleus(of(almost(all(cells.(

•  Chromosomes(contain(sections(called(genes(•  Genes(are(made(of(DNA(•  Genes(blueprint(the(production(of(proteins(



The(bonding(and(structure(of(DNA(

•  DNA((deoxyribonucleic(acid)(is(a(condensation(polymer(

•  There(are(four(nucleotide(monomers(•  Nucleotides(are(made(up(of(three(molecules(joined(by(condensation(reactions(–(a(sugar((deoxyribose)(

a(phosphate(group(and(one(of(four(different(

organic(bases(–(adenine,(thymine,(cytosine(and(

glycine(



Structure(of(the(bases(is(in(the(VCE(Chemistry(

data(book(

Adenine(and(guanine(are(purine(bases(

cytosine(and(thymine(are(pyramidine(bases(



Formation(of(nucleotides(

•  Carbon(1(of(the(sugar(bonds(to(the(organic(base(and(carbon(5(of(the(sugar(bonds(to(the(

phosphate(group(in(condensation(reactions(

(water(released).(

•  These(structures(are(in(the(data(book((table(10)(

1



Condensation(reactions(to(form(the(

polynucleotide(chain(



Degrees(of(DNA(structure(

•  Primary(structure(–(order(of(nucleotides(•  Held(together(by(covalent(bonding((

•  Secondary(structure(–(held(together(by(hydrogen(bonding.(

•  DNA(is(made(up(of(two(strands(•  Organic(bases(pair(up(with(corresponding(base(on(second(DNA(strand(using(HP

bonding.(



Hydrogen(bonding(between(the(bases(



•  Tertiary(structure(–(negative(charge(due(to(phosphate(groups(allows(DNA(to(supercoil(around(

proteins(called(histones.(

•  This(tight(packaging(creates(a(chromosome.(



Sample(exam(question(P(DNA(

In(the(piece(of(doublePstranded(DNA(shown,(the(letters(A,C,(G(and(T(represent(the(bases(adenine,(cytosine,(

guanine(and(thymine(respectively.(Each(vertical(line(

represents(a(sugarPphosphate(backbone.(

(

Which(of(the(following((

alternatives(correctly(

identi@ies(the(DNA(piece(

that(is(most(readily((

separated(by(heating(

and(the(strand(of(the(

highest(molecular(mass?(

(

VCAA(June(2008(Q10(



Use&the&data&booklet!&

Piece(most(readily(separated(by(

heating(

Strand(of(highest(molecular(mass(

A.( 1( X(

B.( 2( W(

C.( 2( X(

D.( 1( W(




Biochemical Fuels

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CHEMISTRY



Key(Knowledge(

! organic(reaction(pathways(including(appropriate(equations(and(reagents:(

–(production(of(biochemical(fuels(including(

the(fermentation(of(sugars(to(produce(

ethanol(



Biochemical(fuels((biofuels)(

! These(are(fuels(derived(from(plant(materials(such(as(grains,(sugarcane(or(vegetable(waste(

(biomass),(and(vegetable(oils.(

! They(may(be(used(alone(or(mixed(with(fossil(fuels.(

! Ethanol(and(biodiesel(((((are(the(most(common(

(((((biofuels.(



! Biofuels(are(considered(carbon(neutral(because(they(are(made(from(plants(which(used(CO2(for(

photosynthesis,(so(when(they(are(burnt(that(same(

CO2(is(returned.(

! Recall(the(equation(for(photosynthesis:(6CO2(g)(+(6H2O(l) ( ((C6H12O6(aq)((+(6O2(g)(

(

! Combustion(of(ethanol:((((((C2H5OH(l)((+((O2(g)((→((2CO2(g)((+((3H2O(l)(

sunlight!!!→



Ethanol(

! Made(by(the(fermentation(of(sugars(! This(is(an(anaerobic((in(the(absence(of(O2)(process(

C6H12O6(aq)( ( ((2(C2H5OH(aq)((+(2CO2(g)(

&

! The(product(is(not(pure(ethanol(–(only(about(20%,(so(must(be(distilled(to(purify.(

! Recall(that(distillation(uses(the(difference(in(boiling(points(of(liquids(to(separate(them(

enzymes!!!→



Distillation(



Production(of(ethanol(as(a(‘green’(

process(•  CO2(from(the(fermentation(is(sold(to(soft(drink(manufacturers.(

•  5%(petrol(is(added(to(prevent(people(drinking(it.(•  Waste(water(used(for(irrigating(crops(•  Remains(of(fermentation(used(for(feedstock.(•  Recycle(byproducts(as(fertiliser(



Biodiesel(

•  This(is(a(mixture(of(esters(produced(by(a(chemical(reaction(between(vegetable(oil(and(an(alcohol(such(

as(methanol.(

•  The(properties(of(biodiesel(are(very(similar(to(those(of(diesel,((

•  In(virtually(all(models(of(equipment(and(vehicles(currently(in(production,(a(biodiesel(blended(fuel(is(

compatible.((

•  Raw(materials:(fresh(vegetable(oils(or(recycled(vegetable(oil(or(animal(fats.(



How(biodiesel(is(made:(

•  The(triglyceride(is(hydrolysed&by(warming(it(with(KOH(aq).(

•  KOH(also(acts(as(a(catalyst(•  Overall(the(triglyceride(breaks(down(to(three(fatty(acid(molecules,(plus(glycerol.(

•  Methanol(is(added(and(reacts(with(the(fatty(acid(to(make(biodiesel.(



Equation(for(the(formation(of(

biodiesel(



Biogas&

•  Equal(mix(of(CO2(and(methane(((CH4)(•  Generated(when(organic(material(decomposes(in(the(absence(of(oxygen.(

•  Particularly(suited(to(farms(



•  Lots(of(sources(of(organic(waste(can(be(adapted(to(biogas(generation.(

•  eg(Werribee(waste(treatment(plant(– Rubbish(tips(– Chicken(farms(– Piggeries(– Food(processing(plants(



Sample(exam(question(P(biofuels(A(product(derived(from(palm(tree(oil(is(used(as(an(alternative(fuel(in(diesel(engines.(Palm(oil(is(converted(to(biodiesel(by(the(following(reaction(

(

(

(

(

(

(

Glycerol(is(separated(from(the(reaction(mixture.(The(mixture(of(the(compounds(labelled(X,(Y(and(Z(is(used(as(palm(oil(biodiesel.(The(term(that(best(describes(the(mixture(of(compounds(in(palm(oil(biodiesel(is(

A.  Methyl(esters ( (B.((carbohydrates(((

C.  Carboxylic(acids ( (D.((monoglycerides(

VCAA(June(2009(Q18(

(




The Design and Synthesis of Medicines including Aspirin

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CHEMISTRY



Key(Knowledge(

•  organic(reaction(pathways(including(appropriate(equations(and(reagents:(

P  function(of(organic(molecules(in(the(design(and(synthesis(of(medicines(including(the(production(of(

aspirin(from(salicylic(acid.(



Aspirin((•  Aspirin(is(an(ester.(•  It(is(derived(from(salicylic(acid(which(was(known(as(a(pain(killer(and(reduced(fever(but(

caused(irritation(to(the(lining(of(the(stomach(

and(the(mouth.(

•  The(full(name(of(aspirin(is(acetyl(salicylic(acid.(•  Aspirin(is(much(less(irritating(to(the(stomach(and(mouth(than(salicylic(acid.(

•  It(is(broken(down(into(salicylic(acid(in(the(alkaline(surroundings(of(the(small(intestine.(



Preparation(of(Aspirin(

•  Aspirin(can(be(made(by(two(different(pathways(

•  Salicylic(acid(+(ethanoic(acid(



•  Or(salicylic(acid(+(ethanoic(anhydride(



•  Alkaline(hydrolysis(breaks(aspirin(down(

•  Aspirin(can(be(made((soluble(by(creating(a((

sodium(salt.(



Another(example(P(Penicillin(

•  An(example(of(a(drug(developed(after(chance(observations(in(the(lab.(

•  A(culture(of(staph(bacteria(was(growing(and(a(mould(which(grew(on(the(plate(by(mistake(was(found(to(kill(the(bacteria.(

•  Isolation/extraction(of(the(mould(was(dif@icult(when(it(was(@irst(discovered.&

•  Increased(need(for(the(drug((WW2)(and(improved(methods(extraction(12(years(later((1940)(

•  Initially(tested(on(mice,(but(quickly(moved(to(humans(due(to(the(need(to(save(the(lives(of(soldiers(who(were(suffering(from(infections(after(surgery(on(the(battle(@ield.(



Effect&of&changing&the&structure&slightly&

•  Different(side(chains(are(possible(in(penicillin.(•  Stomach(acid((broke(penicillin((

down.((

•  Change(of(side(chain(improved((

stability.(

&



Resistance&to&drugs&

•  Bacteria(reproduce(very(rapidly(•  Those(bacteria(that(are(slightly(different(and(can(survive(the(drug,(get(to(reproduce(and(so(a(strain(

of(drug(resistant(bacteria(are(created.(

•  Taking(a(full(course(of(antibiotics(minimises(the(chance(of(bacteria(surviving.(



Developing(a(new(drug(

•  ‘Lead’(compounds(can(potentially(be(made(into(drugs.(

•  Sources(may(be(herbal(or(traditional(((remedies.(eg(aspirin.((

•  Computer(modelling(is(used(for(design(of(speci@ic(drugs(

&



Steps(in(drug(design(

•  Computer(modelling(•  Development(of(synthetic(pathway(•  Formulation(for(administering(drug(is(required(•  Testing(is(needed(–(clinical(trials(•  Comparison(with(placebos(to(see(how(effective(the(drug(actually(is.(

•  Analysis(of(the(drug(tests(purity(



Sample(exam(question(–(functional(

groups(in(drugs(The(compound(salicin(can(be(converted(into(aspirin(using(the(steps(below:(

(

(

(

(

(

(

(

(

VCAA((June(2010(Q(8(

(



(a)(What(type(of(linkage(is(circled(in(the(structure(of(salicin?(

(b) In(step(1,(salicyl(alcohol(and(another(compound(is(produced.((

(((((((i)What(group(of(biomolecules(does(this(compound((

(belong(to?(

((((((ii)(The(structure(of(this(other(compound(is(not(

(complete.(Write(the(formula(of(the(atom(or(group(of((atoms(represented(by(A(in(the(reaction(scheme( (above.(

(c)  Step(2(involves(the(conversion(of(salicyl(alcohol(into(salicylic(acid.(

(i)  What(type(of(reaction(is(step(2?((ii)  Suggest(a(suitable(reagent(to(carry(out(the(reaction.(

(



(d)(Step(3(requires(sulfuric(acid(catalyst(and(another(reagent.(Name(this(reagent.(

(

(

(e)(Aspirin(reacts(with(a(strong(base(according(to(the(equation(

(

(

(

(

Draw(the(structure(of(the(product(B.(

(

vce chemistry unit 3

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