lecture+01+chem+equil+&+grav anal+for+web

Lecture 01 Chemical Equilibrium

1週次日期單元主題第 1週 2/26, 28 Chemical Equilibrium & Gravimetric Analysis (Ch 6 & 7) 第 2週 3/05, 07 Activity & Systematic Treatment of Equilibrium (Ch 12)第 3週 3/12, 14 Buffers & Acid-Base Titrations (Ch 8~10) 第 4週 3/19, 21 Polyprotic Acids & Bases (Ch 11) & EDTA Titrations (Ch 13)第 5週 3/26, 28 EDTA Titrations (Ch 13) & Experimental Error (Ch 3)

第 6週 4/024/04

第一次期中考 (佔學期總成績 30%)Statistics (I) (Ch 4)

第 7週 4/09, 11 Statistics (II) (Ch 4)

第 8週 4/164/18

Quality Assurance and Calibration Method (Ch 5)Fundamentals of Electrochemistry (Ch 14)

第 9週 4/23, 25 Electrodes, ISE, and Redox Titrations (Ch 15 & 16)第 10週 4/30, 5/02 Instrumental Methods in Electrochemistry (Ch 17)

第 11週 5/07, 09 Instrumental Methods in Electrochemistry (Ch 17)

第 12週

5/14,5/16

第二次期中考 (佔學期總成績 30%)Basics of Spectroscopy (Ch 18)

第 13週 5/21, 23 Spectrophotometry: Instruments (Ch 19)

第 14週 5/28, 30 Atomic Spectroscopy (Ch 20)

第 15週 6/04, 06 Principles of Chromatography (Ch 21)

第 16週 6/11, 13 GC & LC (Ch 22)

第 17週 6/18, 20 Electrophoresis (Ch 23)

第 18週 6/25 期末考 (佔學期總成績 40%)


2

Chemical EquilibriumaA + bB ⇌ cC + dD

at equilibrium

_____________

K =[C]c[D]d

[A]a[B]b concentration ratio:([A] or PA) ÷ (standard state,

i.e., M or bar)

the law ofmass action rateforward

= ratereverse

K, equilibrium const

solution: M or mol/Lgas: bar or atm

(1 bar~ 0.987 atm)

ex. pure liquidpure solidsolvent

pure materials: __

ex: ion-product const for water

solubility product const

standard state

2H2O ⇌ H3O+ + OH– K =[H3O+][OH–]

[H2O]2 [H2O]2K = [H3O+][OH–]

[H2O]: enormous concw.r.t. [H3O+] or [OH–]

= [H3O+][OH–]as if [H2O] → 1

Ba(IO3)2(s) ⇌ Ba2+(aq) + 2IO3–(aq)

K =[Ba2+][IO3

–]2

[Ba(IO3)2(s)] [Ba(IO3)2(s)]K = [Ba2+][IO3

–]

= [Ba2+][IO3–]


3

dimensionless


standard state

= e–Go/RT

Chemical EquilibriumaA + bB ⇌ cC + dD

K =[C]c[D]d

[A]a[B]b

Keq = f(, , )

= e–(Ho – TSo)/RT

= e–Ho/RT + So/R

Le Chaterlier's Principle

Go < 0 Keq

[products]standard state [reactants]

standard state spontaneous rxn (i.e., rxn direction: ___)

Keq = f(T)

Ho or So rxn direction: ___

Ho >< 0 when T e–Ho/RT Keq

Q: favored rxn direction when T ?A: it _________ whether the rxn is

____thermic or ___thermic

Q: rxn quotient predicting the rxn direction (p 99) Q >< Keq

favored rxn direction


the position of a rxn shifts toward the directionthat relieves the effects of the disturbance

heat/temperature: treated as if reactant/product


4

important equilibria in analytical chemistry

name ofequil constion-productconst

solubilityproduct

dissociationconst

formationconst

redoxconst

distributionconst

Skoog 8th edp 235, Table 9-2


5

Harris Fig 10-11 (7th ed)

Ka & Kb

acids/bases

http://web.jjay.cuny.edu/~acarpi/NSC/7-ph.htm

http://www.science.uwaterloo.ca/

~cchieh/cact/c123/stacids.html

Arrhenius

Brnsted-Lowry

Lewis

acid/base notes

_________

______ donorsacceptors

__ acceptorsdonors

limited to _______ soln

applicable to ___aqueous soln

more generalized;applicable to

organometallicsQ: Regarding the rxn:NH3(g) + HCl(g) ⇌ NH4Cl(s)is HCl an Arrhenius acid?

A: ___

Q: advantage of the concept ofBrnsted-Lowry acids/basesin titrimetry?

A: leveling effect (11.8) Ka of HClO4 & HCl

in water? leveling solvent differentiating solvent ex: titration in Me-C(O)-i-Bu

(methyl isobutyl ketone)w/ Bu4N+OH– (TBAOH)

acidity: HClO4 HClBF3 + NH3 ⇌Ni2+ + 6NH3 ⇌ Ni(NH3)6

2+

examples of Lewis acids/bases


6

Ka & Kb (section 6.5~6.7)

proton/hydronium ion (hydroxonium)

H2O + H2O ⇌ H3O+ + OH– Kw = [H+][OH−] = 1.0 x 10−14

proton does not exist by itself in water.

autoprotolysis

cluster ingas phase

in aqueoussolution

ion-dipoleattraction

protic/aprotic solvent protic: chemistry involving proton transfer

from one molecule to another protic solvent: having a reactive H+

aprotic solvent:no acidic H+, eg. CH2Cl2

NH3 + NH3 ⇌ NH4+ + NH2

–

AcOH + AcOH ⇌ AcOH2+ + AcO–

temp-dependent

oC pKw0 14.938

25 13.99550 12.265

pH pH = –logAH+ ≈ –log[H+]

Q: is there such a thing as Pure Water?

pH ≈ –log[H+], an approximation

Q: find pH of neutral soln at 50 oCA: pH ~

pH = 7.0 for neutral soln:true ____ at 25 oC

activity = conc x act. coeffAC = [C]C eq 8-4

A: no, if no precaution for___ + H2O ⇌ HCO3

– + __


7

dative/coordinate covalent bond: a bond betweena Lewis acid & a Lewis base

n or Ki

complex formation Lewis acid + Lewis base ⇌

formation constant n: _______ Ki: _______

formation constant

n = K1 x K2 x ... x Kn

ex: Pb2+ + 4I– ⇌ PbI42–

Pb2+ + I– ⇌ PbI+

PbI+ + I– ⇌ PbI2(aq)

PbI2(aq)+ I– ⇌ PbI3–

PbI3– + I– ⇌ PbI4

2–

K1

K4

K3

K2

=[PbI+]

[Pb2+][I–]

= [PbI42–]

[PbI3–][I–]

4 = K1 x K2 x K3 x K4

= [PbI2(aq)][PbI+][I–]

[PbI3–]

[PbI2][I–][PbI4

2–][PbI3

–][I–]

[PbI+][Pb2+][I–]

=[PbI4

2–][Pb2+][I–]4

rxns Keq = n

= K1 x K2 x ... x Kn


8

Ksp

to find ion conc (if the conc of the other(s) is(are) known)

common ion effect:____ soluble for a salt when one of its constituents already present

ex: given that Hg2Cl2(s) ⇌ Hg22+ + 2Cl–

MXn(s) ⇌ Mp+(aq) + nXq–(aq) Ksp = [Mp+][Xq–]n

Q: find (1) [Cl–] in pure water(2) solubility of Hg2Cl2 in pure water(3) solubility of Hg2Cl2 in 0.10 M KCl soln

Ksp = [Hg22+][Cl–]2 = 1.2 x 10–18

ex: given that solubility for KCl is 3.7 M(i.e., Ksp ≈ ___ x ___ = 13.7)explain the different behaviorsbetween the two test tubes (p 102)

6 M 12 M

1 volume sat'd KCl(aq)

w/o precipitant

homo-geneoussoln

KCl(s)

add 1 volumeof HCl(aq) ex: SCaSO4

= f(dissolved CaCl2)

Harris Fig 6-1, 7th ed


9

Harris Fig 6-1, 7th ed

ex: SCaSO4

= f(dissolved CaCl2)

Ksp

to find ion conc (if the conc of the other(s) is(are) known)


common ion effect

ex: for a soln containing 0.010 M Pb2+ & 0.010 M Hg22+

given that Hg2I2(s) ⇌ Hg22+ + 2I– Ksp = [Hg2

2+][I–]2 = 1.1 x 10–28

PbI2(s) ⇌ Pb2+ + 2I– Ksp = [Pb2+][I–]2 = 7.9 x 10–9

Can [I–] be used to precipitate 99.99% Hg22+

and to keep Pb2+ soluble in soln?

simple cases: no rxns other than Ksp involved

A: [Hg22+] = S; [I–] = __

Ksp = [Hg22+][I–]2 =

S =

separation by precipitation

solubility of salts

ex: find solubility of Hg2I2 in pure watergiven that Hg2I2(s) ⇌ Hg2

2+ + 2I–

Ksp = [Hg22+][I–]2 = 1.1 x 10–28

complicated cases:other rxns also taking place,such as hydrolysis, disproportionation,

ion pairs, complex formation, redox, ... ...

= [Ca2+] + [CaSO4(aq)]

Hg22+ + H2O

⇌ Hg2OH+ + H+

Hg22+ ⇌ Hg2+ + Hg()


10

solubility solubility of salts


complicated cases: when [Xq–] precipitate MXn may redissolve as MXij–

ex: Pb2+ + 4I– ⇌ PbI42–

Pb2+ + I– ⇌ PbI+

PbI+ + I– ⇌ PbI2(aq)

PbI2(aq)+ I– ⇌ PbI3–

PbI3– + I– ⇌ PbI4

2–

K1

K4

K3

K2

=[PbI+]

[Pb2+][I–]

= [PbI42–]

[PbI3–][I–]

2=[PbI2(aq)][Pb2+][I–]2

Q: write solubility of PbI2(s) = f([I–])A: S = [Pb2+] + [PbI+] + [PbI2(aq)] + [PbI3

–] + [PbI42–]

i.e., find [Pb2+], [PbI+], ... ... , [PbI42–] = f( )

[Pb2+] = Ksp/[I–]2

[PbI+] = K1[Pb2+][I–]

[PbI2(aq)] = K2[PbI+][I–]= __________

[PbI3–] = K3K2K1[Pb2+][I–]3 = 3[Pb2+][I–]3

[PbI4–] = K4K3K2K1[Pb2+][I–]4 = 4[Pb2+][I–]4

= K2_____[I–]2

Pb2+ + 2I– ⇌ PbI2(aq)

Q: find solubility of PbI2(s)when [I–] = (a) 1.0 mM, (b) 1.0 M

A: S = [Pb2+] + [PbI+]+ [PbI2(aq)]+ [PbI3

–] + [PbI42–]

put the #s into the eqns straightforward

Q: which formdominate the solubility?

A:


11

solubility (Ksp, ion pairs, charged complexes)

solubility of salts complicated cases: when [Xq–] precipitate MXn may redissolve as MXi

j–

Harris Fig 6-3

A: S = [Pb2+] + [PbI+] + [PbI2(aq)]+ [PbI3

–] + [PbI42–]

[Pb2+] = Ksp/[I–]2

[PbI+] = K1[Pb2+][I–][PbI2(aq)] = 2[Pb2+][I–]2

[PbI3–] = 3[Pb2+][I–]3

[PbI4–] = 4[Pb2+][I–]4

ex: solubility of PbI2(s) at 1.0 mM & 1.0 M

7.9 x 10–3

[I–] = 1.0 mM & 1.0 M

7.9 x 10–4

1.1 x 10–5

6.6 x 10–8

2.4 x 10–10

7.9 x 10–9

7.9 x 10–7

1.1 x 10–5

6.6 x 10–5

2.4 x 10–4

Solubility = 8.7 x 10–3

+

3.2 x 10–4

Q: why do complex formsdominate solubility when [I–] ?

Q: why does [PbI2(aq)] ≠ f([I–])?A: [PbI2(aq)] = 2[Pb2+][I–]2


12

Skoog Fig 11-2

solubility (Ksp, ion pairs, charged complexes)

solubility of salts complicated cases: when [Xq–] precipitate MXn may redissolve as MXi

j–

ex: solubility of AgCl(s) is cKCl–dependent

Q: why does[AgCl(aq)] ≠ f([Cl–])?

Q: why docomplex formsdominate solubilitywhen [Cl–] ?

AgCl ⇌ Ag+ + Cl– Ksp = [Ag+][Cl–]= 1.8 x 10–10

A: S = [Ag+] + [AgCl(aq)] + [AgCl2–] + [AgCl3

2–]


13

precipitate gravimetric analysis (Chapter 7)

general concept

A: introduce ______ Ag+ collect & weigh AgCl(s) calculate mole of precipitate calculate [Cl–]

ex: how to find [Cl–] in an aqueous soln AgCl ⇌ Ag+ + Cl– Ksp = [Ag+][Cl–]= 1.8 x 10–10

ex: find [Cl–] in a 10.00-mL aqueous solngiven that treatment with excess AgNO3

resulting in precipitate of 0.4368 g of AgClA: mol of Cl– = mole of AgCl(s)

= [wt of AgCl(s)]/[(formal mass of AgCl)]= 0.4368/143.321= 3.048 x 10–3 mol

[Cl–] = (3.048 x 10–3 mol)/(10.00 mL) = 0.3048 M

( selective (not specific)–Table 27.1Ksp, AgCl: sufficiently small Ag+: precipitant for Cl–)

Q: how good is the result?what may cause false results

—heavier/lighter than the theoretical wtdesired properties of precipitate

for gravimetric analysis?

A: very pure, easily filterable, known composition math: easy; good precipitate: difficult

ideal precipitate: large & crystalline

Ci−

excessAg+

AgCl

Harris Fig 6-3

Q: disadvantages ofsmall particles of precipitate?

A: colloidal suspension ___ precipitating

________ filter passing filter false resultslarge ________ impurity

adsorption


14

determination of [Cl–] in soln (Skoog 37B-1)


15

Gravimetric Determination [Cl–] in a soluble sample

Harris Fig 2-12


16


HarrisFigs 2–14

17


17


http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/labtech/trans2.jpg


18


http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/labtech/filter3.htm

place & wetthe filter paper


19

relative supersat'n

mech of precipitate formation & expt'l strategies general concept

ideal precipitate: large & crystalline mech of crystal growth mixing reagents → nucleation & particle growth

expt'l strategies Q term:

as few as 4~5 nuclei form stable clusters

& ads on dusts/contaminants super-saturation

relativesupersat'n

mixing analytew/ precipitant

nucleation

furthernucleation

particlegrowth

=

Q: Csolute at ___ instantS: ________ at equilibrium

S term:

dilution Csolute ______ adding precipitant

T S

______ while adding precipitant

adjusting soln pH for those w/ S = f(pH)

Harris Fig 6-3

Cl–

excessAg+

AgCl


20

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–

NO3–NO3

–

NO3–

NO3–

NO3–

NO3–

NO3–

H+

H+

H+

H+

H+

2d2

2d1

particle counter-ionlayer

effect of electrolyte on precipitation & expt'l strategies electrical double layer of a colloid

expt'l strategies Q term: S term:

excess precipitant Qads dctr-ion layer

primary adsorption layer originated from bonding forces for crystal growth resulting in excess/___ surface ______

counter-ion layer driven by electroneutrality excess # of counter ions

preventing colloidsfrom colliding/precipitation

strength of chemisorption: Agads > Hads

bond strength: Ag−Cl > H−Cl

repulsion/stability of colloids= f(dcounter-ion layer)

Celectrolyte densityctr ion dctr-ion layer

Celectrolyte:

d: thickness ofcounter ion layer

heating adsorbility Qads

stirring Ek overcome Erepulsion

heating stirring Skoog Fig 12-1~3Harris Fig 7-2


21

coprecipitation

types of coprecipitation

—introducing contaminants/impurity coprecipitation errors

—species that should be _______is precipitated along with the desired product

soln ____ ______________ forms

a process thata coagulated colloid______ _____

losing weakly bound water ______ solid/smaller surf area easier to filter

digestion

washing

reprecipitation

surface adsorption mixed-crystal formation: lattice sites occupied by

impurities w/ properties similar to those of analyte

occlusion: ions in the counter-ion layerare _______ in the ______ formed during particle growth

methods to remove impurities/improve purity

precipitate is heated (w/o stirring) for ~1 hr in mother liquor

a process after filtration to remove impurity washed w/ pure water dctr-ion layer peptization washed w/ soln containing ________ electrolyte

ex: washing AgCl(s) w/ diluted HCl which evaporates later upon drying (high T)

redissolve the filtered solid & reprecipitate it

effective (but )redissolved soln: ____ contaminants

ex: SrSO4 in BaSO4MnS in CdS


22

homogeneous precipitation

drying & ignition of precipitates

—precipitating agent:homogeneously & slowlygenerated throughout the soln

aluminum hydroxide

NH4OH (H2N)2COex:

Q – SS

very small __ in ________ ______Skoog Fig 12-5

(Harris p 137 & Table 7-3)

1~2 hrs

const mass& known compositionex:

removal of solvent, volatile species decomposition

purpose: to obtain the weighing form

Harris Fig 7-3

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