3.2.9 alkenes - mrmortonsciencemrmortonscience.weebly.com/uploads/3/1/5/7/31575951/_3.2... · 2020....

3.2.9 Alkenes

Addition Reactions

271 minutes

268 marks

of 39

M1. (a) Electrophile: e– pair / lone pair acceptor or e– deficient species or e–

seeking species (1) For ‘species’ accept atom, molecule, ion NOT ‘+’ ion NOT ‘attracted to ‘-’ charge’

Addition: reaction which increases number of substituents or convert double bond to single bond or where two molecules form one molecule (1)

2

(b) (High) e– dense or e– rich C=C or e– rich π bond or 4 e– between the C’s (1)

NOT just ‘C=C’

causes induced dipole in Br2 (1)

Ignore refs to ‘temporary’

can score M2 from δ+ / δ– on Br2 in (c) unless a contradicting error

in (b) 2

(c) Mechanism:

If incorrect alkene, lose M3 (wrong cation) Mark M4 conseq on M3

Name of product: 1,2-dibromopropane (1) 5

(d) addition (1) Not additional

1 [10]

M2. (a) (i) Reagent: Hydrogen of H2 (1)

Conditions: Ni (catalyst) (Ignore Pt) (1) 100 – 200 °C or heat (1)

Not ‘high temp’ or ‘warm’ M1 = 0, M2 = 1 then M3 = 0 max or M1 = M2 = 0 then M3 = 0 M3 tied to M1. Only award M3 if M1 earned

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(ii) Difference in structure: soft margarine less hydrogenated or has more C=C bonds or is more unsaturated than hard margarine (1) Difference in melting point: soft has lower melting point (1)

Must be comparison 5

(b) (i) 3-methylbutan-2-ol (1) No alternatives

(ii) elimination or dehydration (1)

(iii) (c) H2SO

4 or (c) H

3PO

4 – name or correct formula (1)

(iv)

Double bond must be shown Accept any correct unambiguous structures if but- 1-ene and but-2-ene offered, allow M2

5 [10]

M3. (a) % O = 21.6 % (1) If % O not calculated only M2 available

Ratio: 4 : 10: 1 ( C4H

10O) (1)

If arithmetic error in any result lose M3 If percentage composition calculation done zero

3

= 5.41 = 13.5 = 1.35

(b) (i) Type of alcohol: Tertiary (1) Reason: No hydrogen atom on central carbon (1)

C

H

O (1)

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Penalise missing bonds / incorrect bonds once per paper 4

(c) (i) Aldehyde (1) Ignore named aldehydes or their structures, penalise wrong named compound

(ii) CH3CH

2CH

2CH

2OH + [O] → CH

3CH

2CH

2CHO + H

2O (1)

Balanced (1) C

4H

10O is OK as a reactant

[O] can be over arrow C

3H

7CHO not accepted for product, but C

2H

5CH

2CHO is OK

If use C3 or C

5 compounds no marks in (ii) C.E of wrong alcohol

(iii) Name Butanoic acid (1) Structure: CH

3CH

2CH

2COOH (1)

mark conseq. or as stated 5

(d) Advantage: Fast reaction OR pure product OR continuous process OR cheap on manpower OR high yield, 100% alcohol (1) Disadvantage: High technology OR ethene from non renewable source OR expensive equipment not just costly (1)

Not answers based on fermentation 2

(ii)

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(e)

4

[18]

M4.May circle 4 C’s separately

1

(b)

Ignore δ+ and δ- unless wrong

4

(c) Reagent: H2O or water OR steam, Or dilute sulphuric acid (1)

Condition: heat, or warm, or boil or reflux [50-100°C] (1) Name of compound C: 2-methylbutan-2-ol (1)

Allow 2-methylbutane-2-ol Penalise hydroxy-2-methylbutane and 2-methylbut-2-ol once only in the paper

3

(a)

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(d) Identity of alcohol D: 2-methylbutan-1-ol (1), OR its structure, could describe structure

Explanation: C formed via t-carbocation; D via p-carbocation, (1) tertiary more stable than primary (1)

If have wrong carbocation can still score stability mark 3

[11]

M5. (a) (i)

If wrong carbocation, lose structure mark If wrong alkene, lose structure mark Can still score ¾ i.e. penalise M3 Penalise M2 if polarity included incorrectly no bond between H and Br bond is shown as or

(ii) credit secondary carbocation here if primary carbocation has been used in (i)

Ignore attack on this carbocation by 5

(b) (i) Structure:

No credit for propan-1-ol even when named correctly Credit propane-2-ol

Name: propan-2-ol (1) Not 2-hydroxypropane

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(ii) Name of mechanism: nucleophilic substitution (1) (both words) (NOT S

N1 orS

N2)

Mechanism:

penalise incorrect polarity on C-Br (M1) Credit the arrows even if incorrect haloalkane If S

N1, both marks possible

5

(c) (i) elimination (1) Ignore nucleophylic elimination Penalise electrophilic elimination

(ii) base (1) OR proton acceptor NOT nucleophile (base)

2 [12]

M6. (a) ethan(e)-1,2-diol OR 1,2-ethan(e)diol (1) antifreeze (1) OR production of Terylene / polyester feedstock for polyester / PET

NOT surfactant NOT plasticizer NOT solvent NOT de-icer 2

(b) Reaction 1 H2O or steam (1)

Reaction 2 O2 (1) NOT air

Ignore reaction 3

Reaction 4 H2O (1)

Reaction 5 NH3 (1)

For Reaction 4; credit dil H2SO

4 OR H

2SO

4(aq) OR HCl (aq) but

NOT steam and NOT NaOH(aq) 4

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(c)

Penalise M2 incorrect δ+ / δ–

Penalise δ– on alkene (M1)

Penalise dots on bonds once Penalise M4 (structure) for use of wrong alkene Penalise M1 for use of Br

2

4

(d) Water OR aqueous solution OR (aq) in equation (1) M1

Yeast OR enzyme/zymase OR T 45°C but T not below 20°C and allow warm

N.B. yeast and T=60° con Ignore pH Ignore anaerobic / oxygen Ignore time Ignore pressure

M2

C6H

12O

6 → 2C

2H

5OH (or CH

3CH

2OH) + 2CO

2

Allow C12H

22O

11 if balanced equation

M4 OR M5 needs the use of good English and correct chemistry to gain credit

M3

M4: The rate of fermentation is slower (1) OR The rate of hydration is faster

QoL OR (The rate of) fermentation is slow and (the rate of) hydration is fast

reference correctly to time rather than rate gains credit

M5: The product of fermentation is less pure or lower purity OR The product of hydration is more pure or higher purity OR The product of fermentation is impure and that of hydration is pure OR Specific reference to 10–15% versus 90–100% OR correct reference to higher or lower yield

5 [15]

M7. (a) (i) Electrophilic addition

(Both words required) 1

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(ii) M1 the reaction to form 1-bromopropane goes via the primary carbocation OR 1o carbocation

M2 primary carbocations are less stable than secondary carbocations (Credit converse arguments for M1 and M2 i.e. the reaction to form 2-bromopropane goes via the secondary carbocation , M1, and secondary carbocations are more stable than primary carbocations, M2) (Accept the use of “carbonium ions” as an alternative to carbocation)

1

(b) M1 NaOH OR KOH OR correct name 1

M2 aqueous or solution in water (ignore heat, reflux etc.) (Penalise M1 for hydroxide ion alone, but mark on and credit M2) (Credit M2 ONLY for H

2O as reagent and heat / warm / T=50 to

100oC) (NaOH(aq) scores M1 and M2 provided it is not contradicted) (Penalise M2 if NaOH(aq) followed by concentrated or ethanol) (Penalise M1 and M2 if followed by acid)

1

(c) Ethanolic OR alcoholic OR CH3CH

2OH / CH

3OH solvent OR

aqueous ethanol/alcohol OR higher temperature (must be comparative)

(Ignore heat or heat under reflux) (Credit part (c) independently from part (b)) (Penalise “ethanoic”)

1

OR via

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(d) (i) Secondary OR 2o

1

M1 arrow from double bond to H of H – O bond M2 arrow from bond to oxygen atom to show H – O bond breakage M4 arrow from lone pair of electrons to carbon atom of carbocation

(Penalise M1 if arrow goes to H2SO

4 or to formal positive charge on

H, but ignore partial charges on sulphuric acid unless wrong)

(Credit M2 for H+ ion)

(For M4, accept negative charge anywhere on the ion) 4

(iii) Catalyst ONLY (Ignore homogeneous, heterogeneous)

1 [12]

M8. (a) M1 X is 1,2-dibromoethane only 1

M2 electrophilic addition (both words needed)

1

M3 the double bond is a centre of electron density OR electron-rich OR nucleophilic OR a source of an electron pair OR a pi cloud/bond of electrons

1

M4 a dipole or polarity is induced/created/formed in the Br-Br bond/molecule - award this mark only if the quality of language justifies the award.

1

(ii)

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(b) nucleophilic substitution (both words needed)

1

Mechanism M1 curly arrow from lone pair on oxygen of hydroxide ion to C atom of C-Br

1

Mechanism M2 curly arrow from C-Br bond to side of Br atom (a possible repeat error here from Question 4a) (award a maximum of one mark for the wrong haloalkane) (credit an SNl mechanism in which Ml will be a curly arrow from the lone pair on oxygen of the hydroxide ion to the correct positive carbon atom)

1

Y is susceptible to attack by hydroxide ions for one of the following reasons

o the C-Br bond is polar

o the carbon atom is partially positive (or shown as such)

o the carbon atom is electron deficient 1

(c) M1 oxygen (ignore “air”)

1

M2 silver or silver-based (penalise silver nitrate)

1

M3 Z is epoxyethane 1

M4 epoxyethane

o has a strained ring structure

o has a bond angle of 60°

o has a bond angle significantly less than tetrahedral (ignore “unstable”, “has strained bonds”, “is stressed”)

1

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(d) Ethane-1,2-diol is used in antifreeze OR in the manufacture of PET/Terylene/polyester

(penalise “solvent” or “plasticiser”) 1

Hazard in Route via X/Y

o bromine is toxic or corrosive

o sodium hydroxide is corrosive or caustic 1

Hazard in Route via epoxyethane

o risk of explosion in reaction 4

o epoxyethane is toxic

o epoxyethane is a respiratory irritant

o epoxyethane causes neurological damage 1

[15]

M9. (a) M1 fermentation 1

M2 dehydration or elimination 1

(b) (i) yeast OR zymase OR an enzyme 1

(ii) concentrated sulphuric or phosphoric acid (penalise aqueous or dilute as a contradiction)

1

(c) (i) primary or 1° 1

(ii) sugar or glucose or ethanol is renewable OR ethanol does not contain sulphur-containing impurities OR ethanol produces less pollution or is less smoky or less CO/C

(the objective is a positive statement about ethanol) (penalise the idea that ethanol is an infinite source or vague statements that ethanol has less impurities) (penalise the idea that ethanol produces no pollution)

1

(d) C2H

6 → C

2H

4 + H

2

1

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(e) Addition (ignore self or chain as a preface to “addition “) (penalise additional)

1 [8]

M10. (a) M1 curly arrow from lone pair on oxygen of hydroxide ion to H atom on C-H adjacent to C-Br

1

M2 curly arrow from single bond of adjacent C-H to adjacent single bond C-C

(only credit M2 if M1 is being attempted to correct H atom) 1

M3 curly arrow from C-Br bond to side of Br atom (credit M3 independently)

1

(b) Ml credit a correct structure for either geometrical isomer and its designation as either cis or trans. OR credit two correct geometrical isomer structures (ignore the names) OR credit two correct names for cis pent-2-ene and trans pent-2-ene (ignore the structures)

1

M2 credit a second mark if all four parts of the required structures and names are correct.

(credit “linear” structures) (insist on the alkyl groups being attached clearly by C-C bonds)

1

(c) (i) Ml curly arrow from middle of C = C bond to H atom on H-Br (penalise M1 if partial negative charge or formal positive charge on H) (penalise Ml if pent-2-ene is used)

1

M2 curly arrow from H-Br bond to side of Br atom 1

M3 correct structure for correct secondary carbocation 1

M4 curly arrow from lone pair on bromide ion to the positive carbon of carbocation, ensuring that bromide ion has a negative charge.

(with the exception of pent-2-ene, if the wrong alkene is used, only penalise the structure M3) (penalise the use of two dots in addition to a covalent bond, once only)

1

(ii) 1-bromopentane 1

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(iii) Ml 2-bromopentane is formed via the secondary (or 2°) carbocation

1

OR 1-bromopentane is formed via the primary (or 1°) carbocation M2 a secondary carbocation is more stable than a primary carbocation - award this mark only if the quality of language justifies the award.

(the argument must involve clear statements about carbocations) 1

[12]

M11. (a) (i) C6H

12O

6 → 2C

2H

5OH + 2CO

2;

(penalise C2H

6O once only in this question)

1

(ii) Concentrated H2SO

4 OR concentrated H

3PO

4 OR Al

2O

3;

(penalise aqueous or dilute as a contradiction) 1

C2H

5OH → C

2H

4 + H

2O OR C

2H

5OH → H

2C = CH

2 + H

2O;

(penalise CH2

.CH2 and CH

2-CH

2 and CH

2 : CH

2 for ethene)

1

(b) Nickel OR Ni OR platinum OR Pt OR palladium OR Pd; 1

Hydrogen OR H2;

1

(c) (i) C18

H34O

2 Only;

1

C9H

17O Only;

(empirical formula is not consequential on molecular formula) 1

(ii) (An unsaturated compound) contains (at least) one double bond

OR

Contains C=C; (must be a positive statement)

1

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(iii) M1: Bromine water

OR

Br2(aq)

OR

Bromine

OR

Br2;

(penalise “bromide water”, but mark on) 1

M1: decolourised or goes colourless

OR

from brown/red/orange/yellow to colourless; (Must be “colourless” not “clear” for M2) (chemical error if no reagent or wrong reagent, loses both marks) (credit KMnO

4 for M1, (purple) to colourless for M2 (if acidified)

OR (purple) to brown/brown precipitate (if alkaline or unspecified) (No credit for hydrogen or iodine as reagents)

1 [10]

M12. (a) (i) Electron pair/ lone pair acceptor OR seeking/bonds with an electron pair

(insist on reference to a pair of electrons) 1

(ii) M1 curly arrow from middle of C=C bond of the alkene towards/ alongside the H atom of the H-Br;

(penalise arrows which go towards one of the carbon atoms) (ignore a partial negative charge on the C=C)

1

M2 curly arrow from H-Br bond to side of Br atom; (penalise M2 if there are formal charges on HBr or if there are partial charges which are the wrong) (penalise M2 if the single bond has two dots in addition to the line)

1

M3 correct structure for carbocation; (penalise M3 if the positive charge is placed on the end of a bond) (penalise M3 if any alkene other than ethene is used - all other marks can score)

1

M4 curly arrow from lone pair on bromide ion to the positive carbon of carbocation, ensuring that bromide ion has a negative charge;

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(b) (i) M1 Oxygen OR O2;

(do not credit “air” alone, but otherwise ignore)

M2 silver OR Ag OR silver-based (penalise silver nitrate)

1

(ii) correct structure for epoxyethane; (penalise poorly presented C-O bonds)

1

(iii) water

OR

H2O;

(credit steam OR H2SO

4 (aqueous OR dilute) OR NaOH(aq) OR

HCl(aq), OR H

3PO

4(aq), but insist that (aq) is included)

(do not credit HCl or H2SO

4 (concentrated or without water

present)) 1

(c) (i) M1: potassium cyanide OR KCN OR sodium Cyanide OR NaCN; (ignore conditions - dissolved in (aq) or (alc) or KOH(aq) all work) (penalise HCN)

1

M2: propanenitrile; (credit propan-1-nitrile OR propan nitrile, but not propanitrile)

1

(ii) M1: ammonia OR NH3;

(If formula is written, insist that it is correct) (ignore conditions, but penalise acidic)

1

M2: ethylamine; (credit aminoethane)

1

(iii) M1: curly arrow from lone pair on nitrogen of (correct formula for) ammonia towards/alongside C atom of C-Br;

(penalise M1 if formula of ammonia is wrong or has a negative charge or has no lone pair or arrow is from negative charge)

1

M2: curly arrow from C-Br bond towards/alongside side Br atom; (credit M2 independently) (penalise M2 if formal positive charge on C atom of C-Br)

1

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M3: correct structure of the ethylammonium ion; (credit the structure drawn out with all four bonds around the nitrogen atom OR written as C

2H

5NH

3

+ OR CH3CH

2NH

3

+)

1

M4: curly arrow from the middle of one of the H-N bonds towards the positive N atom;

(possible to credit M4 on an incorrect ethylammonium ion with no positive charge) (ignore use of ammonia or bromide ion etc. to remove proton from ethylammonium ion) (If the wrong haloalkane is used, award MAX. 3 marks for the mechanism) (If S

N1 mechanism is used, give full credit in which

M1 is for a curly arrow from the lone pair of the N atom of (correct formula for) ammonia towards/alongside the positive carbon atom

of CH3CH

2

+)

[17]

M13. (a) Ag or silver or silver-based or silver on an alumina base

(penalise specific silver compounds) 1

epoxyethane 1

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(b) electrophilic addition 1

M1: curly arrow from C=C bond towards/alongside the side of H atom on H-OSO

2OH

(penalise M1 if arrow to H2SO

4 OR to formal charge on H

of H-O bond) (ignore partial charges on H and O of H

2SO

4, but penalise

if these are incorrect on the H atom being attacked) (credit M1 and M2 if correct curly arrow to H+ provided the anion is present)

1

M2: curly arrow from H–O bond towards/alongside the side of the O atom on H–OSO

2OH

(credit the arrow even if there are partial or formal charges on H and O but the structure of H

2SO

4 is correct)

1

M3: correct structure of the carbocation

(penalise use of ‘sticks’ in this structure) 1

M4: curly arrow from lone pair on an individual oxygen atom of (correct formula for) hydrogensulphate ion towards/alongside C atom bearing the positive charge

(insist that the an ion has the correct formula with a lone pair of electrons and a negative charge)

1

(c) (i) ethanal 1

correct structure for ethanal (aldehyde functional group must be drawn out)

1

(ii) oxidation or redox 1

[10]

M14. (a) hydration OR (electrophilic) addition

(penalise incorrect words in front of the word “addition” e.g. “nucleophilic”) (penalise “indirect hydration” but credit “direct hydration” or “steam hydration”)

1

of 39

H2C=CH

2 + H

2O → CH

3CH

2OH

(ignore state symbols) (credit use of C

2H

5OH for ethanol)

(penalise use of C2H

6O for ethanol on the first occasion)

(credit C2H

4 and CH

2=CH

2 for ethene)

(penalise CH2CH

2, CH

2.CH

2, CH

2:CH

2 for ethene on the first

occasion)

(ignore H2SO

4 OR extra H

2O OR H+ if it appears on both sides)

1

conc. H2SO

4 OR conc. H

3PO

4

1

(b) (i) Carbon OR C (credit “soot” or “sooty”) (penalise “coke” or “coal”) (credit “carbon + carbon monoxide” provided it is clear that carbon is solid; penalise “carbon + carbon dioxide”)

1

(ii) CH3CH

2OH + O

2 → 2C + 3H

2O

OR CH

3CH

2OH + 1½O

2 → C + CO + 3H

2O

(credit multiples of these equations) (credit use of C

2H

5OH for ethanol)

(penalise use of C2H

6O for ethanol, but note a possible repeat error

from part (a) above) 1

[5]

M15. (a) Contains a C=C OR a double bond 1

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(b) Electrophilic addition

Both words needed 1

Mechanism:

Ignore partial negative charge on the double bond. M2 Penalise partial charges on bromine if wrong way and penalise formal charges Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M1 Must show an arrow from the double bond towards one of the Br atoms on a Br-Br molecule.

Deduct 1 mark for sticks.

M2 Must show the breaking of the Br-Br bond.

M3 Is for the structure of the secondary carbocation with Br substituent.

M4 Must show an arrow from the lone pair of electrons on a negatively charged bromide ion towards the positively charged carbon atom.

Deduct 1 mark for wrong reactant, but mark consequentially. If HBr, mark the mechanism consequentially and deduct one mark If but-1-ene, mark the mechanism consequentially and deduct one mark. If both HBr and but-1-ene, mark the mechanism consequentially and deduct ONLY one mark.

4

(c) (i) M1 Compounds with the same structural formula

Penalise M1 if “same structure” Ignore references to “same molecular formula” or “same empirical formula”

1

M2 With atoms/bonds/groups arranged differently in space OR atoms/bonds/groups have different spatial arrangements/ different orientation. Mark independently.

1

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(ii)

Award credit provided it is obvious that the candidate is drawing the trans isomer. Do not penalise poor C–C bonds Trigonal planar structure not essential

1 [9]

M16. (a) (i) 3-bromo-3-methylpentane ONLY

Must be correct spelling but ignore hyphens and commas 1

(ii) Electrophilic addition (reaction) Both words needed Accept phonetic spelling

1

(iii) M1 Displayed formula of 2-bromo-3-methylpentane

All the bonds must be drawn out but ignore bond angles

M2 Position(al) (isomerism)

Do not forget to award this mark 2

(iv) Structure of (E)-3-methylpent-2-ene

The arrangement of groups around the double bond must be clear with the ethyl group attached in the correct order. Ignore bond angles. Accept C

2H

5 for ethyl

Be lenient on C ─ C bonds. The main issue here is whether they have drawn an (E) isomer. Accept “sticks” for C ─ H bonds and correct skeletal formula

1

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(b) (i) M1 R is represented by Spectrum 2

M2 Spectrum 2 shows an infrared absorption/spike/dip/ trough/peak with any value(s)/range within the range 1620 to

1680 (cm–1) OR this range quoted/identified and this

is due to C=C OR this information could be a correctly labelled absorption on the spectrum

OR Spectrum 1 does not have an infrared absorption in range 1620 to 1680 (cm–1) and does not contain C=C.

Award M1 if it is obvious that they are referring to the second spectrum (or the bottom one) M2 depends on a correct M1 Ignore other correctly labelled peaks Ignore reference to “double bond” or “alkene”

2

(ii) Functional group (isomerism) 1

(iii) Cyclohexane

OR

Methylcyclopentane etc. Named correctly Ignore structures and ignore numbers on the methyl group of methylcyclopentane

1 [9]

M17. (a) (i) (Free-) radical substitution

Both words needed 1

(ii) UV light/Ultra-violet light/sunlight OR high temperature/150 °C ≤ T ≤ 500 °C

1

(iii) Propagation (Step) Ignore “first” or “second” Accept phonetic spelling

1

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(iv) M1 Termination (Step)

M2 2CH3CH

2CH

2•

C

6H

14

In M2 C

6H

14 may be drawn out as CH

3CH

2CH

2CH

2CH

2CH

3

The dot may be anywhere around the terminal CH2 on the radical

Accept C3H

7• with dot anywhere

Penalise the absence of any radical dot 2

(v) C3H

8 + 8Br

2 C

3Br

8 + 8HBr

Or multiples 1

(b) (i) M1 Double bonds are

electron-rich

OR electron pair donors

OR centres of electron density.

M2 Bromine becomes polarised/becomes polar

OR forms an induced dipole

OR becomes δ+/δ– M1 QoL – require one of these terms Ignore “(very) negative” and “nucleophile” as applied to the double bond. Penalise M2 for ion formation from bromine For M2, do not credit dipole formation solely as a consequence of electronegativity

2

(ii) Electrophilic addition Both words needed Accept phonetic spelling

1

(iii) Structure for 1,2,4,5-tetrabromopentane, for example BrCH

2CHBrCH

2CHBrCH

2Br

OR

Must be clear that they have drawn 1,2,4,5-tetrabromopentane and does NOT need to be displayed Credit use of “sticks” for each C-H bond

1

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(c) +

M1 Structure of CH3CHCH

3

M2 (Secondary) Carbocation OR (secondary) carbonium ions

Mark independently For M1 the positive charge must be on the central carbon atom Penalise bond to positive charge Penalise answers which show more than the correct carbocation e.g. the mechanism, unless the intermediate is clearly identified Credit use of “sticks” for each C-H bond For M2, penalise “primary” or “tertiary”

2 [12]

M18. (a) Position(al) (isomerism) 1

(b)

Penalise one mark from their total if half-headed arrows are used

M1 must show an arrow from the double bond towards the H atom of the H–Br molecule

M1 Ignore partial negative charge on the double bond.

M2 must show the breaking of the H–Br bond.

M2 Penalise partial charges on H–Br bond if wrong way and penalise formal charges

M3 is for the structure of the secondary carbocation.

Penalise M3 if there is a bond drawn to the positive charge

M4 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom of either a primary or secondary carbocation.

Penalise once only in any part of the mechanism for a line and two dots to show a bond Maximum any 3 of 4 marks for wrong reactant or primary carbocation. If Br

2 is used, maximum 2 marks for their mechanism

Do not penalise the use of “sticks”

NB The arrows here are double-headed 4

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(c)

Penalise one mark from their total if half-headed arrows are used

M1 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to a correct H atom

Penalise M1 if covalent KOH

M2 must show an arrow from a C–H bond adjacent to the C–Br bond towards the appropriate C–C bond. Only award if an arrow is shown attacking the H atom of an adjacent C–H (in M1)

M3 is independent provided it is from their original molecule.

Penalise M3 for formal charge on C of the C–Br or incorrect partial charges on C–Br Penalise M3 if an extra arrow is drawn from the Br of the C–Br

bond to, for example, K+

Ignore other partial charges Penalise once only in any part of the mechanism for a line and two dots to show a bond. Maximum any 2 of 3 marks for wrong reactant or wrong product (if shown) or a mechanism that leads to but-1-ene Accept the correct use of “sticks” for the molecule except for the C–H being attacked

Award full marks for an E1 mechanism in which M2 is on the correct carbocation.


[8]

M19. (a) (i)

Penalise one mark from their total if half-headed arrows are used Penalise M3 for formal charge on C of the C-Br or incorrect partial charges on C-Br Ignore other partial charges

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M1 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to the correct H atom

Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M2 must show an arrow from the correct C–H bond to the correct C–C bond. Only award if an arrow is shown attacking the H atom of the correct C–H bond in M1

M3 is independent but CE=0 if nucleophilic substitution

N.B these are double-headed arrows 3

(ii)

Award 1 mark if both correct stereoisomers but in the wrong places Accept no other alkenes. Be reasonably lenient on the bonds to ethyl (or to CH

2CH

3) since

the question is about E and Z positions but penalise once only if connection is clearly to the CH

3 of CH

2CH

3

Accept linear structures 2

(iii) M1 (Compounds / molecules with) the same structural formula

Penalise M1 if “same structure”

M2 with atoms/bonds/groups arranged differently in space

Ignore references to “same molecular formula” or “same empirical formula” or any reference to “displayed formula”

OR atoms/bonds/groups that have different spatial arrangements / different orientation. Mark independently

2

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(b)

M1must show an arrow from the double bond towards the H atom of the H – O bond OR HO on a compound with molecular formula for H

2SO

4

M1 could be to an H+ ion and M2 an independent O – H bond break on a compound with molecular formula for H

2SO

4

M1 Ignore partial negative charge on the double bond.

M2 must show the breaking of the O – H bond.

M2 Penalise partial charges on O – H bond if wrong way and penalise formal charges In M2 do not penalise incorrect structures for H

2SO

4

M3 is for the structure of the carbocation.

M4 must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards a correct (positively charged) carbon atom.

M4 NOT HSO4

–

For M4, credit as shown or –:OSO3H ONLY with the negative

charge anywhere on this ion OR correctly drawn out with the negative charge placed correctly on oxygen Penalise once only in any part of the mechanism for a line and two dots to show a bond

NB The arrows here are double-headed

Max 3 of any 4 marks for wrong organic reactant or wrong organic product (if shown) Accept the correct use of “sticks”

4 [11]

of 39

M20. (a) M1 electrophilic addition

For M1, both words required Accept phonetic spelling

For the mechanism M2 Ignore partial negative charge on the double bond

M2 must show an arrow from the double bond towards the H atom of the H–Br molecule

M3 Penalise partial charges on H–Br bond if wrong way and penalise formal charges

M3 must show the breaking of the H–Br bond Penalise once only in any part of the mechanism for a line and two dots to show a bond

M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the correct (positively charged) carbon atom

Maximum any 3 of 4 marks for the mechanism for wrong (organic) reactant OR wrong organic product (if shown) OR primary carbocation Accept the correct use of sticks

NB These are double-headed arrows 5

of 39

(b) M1 Nucleophilic substitution

For M1, both words required Accept phonetic spelling

For the mechanism Penalise M2 if NH

3 is negatively charged

M2 must show an arrow from the lone pair of electrons on the nitrogen atom of an ammonia molecule to the correct C atom

Penalise M3 for formal charge on C of the C−Br or incorrect partial charges on C−Br

Penalise M3 for an additional arrow from the Br to something else

M3 must show the movement of a pair of electrons from the C–Br bond to the Br atom. Mark M3 independently provided it is from their original molecule

The second mole of ammonia is not essential for M5; therefore ignore any species here

M4 is for the structure of the alkylammonium ion, which could be a condensed formula. A positive charge must be shown on / or close to, the N atom

Penalise once only for a line and two dots to show a bond

M5 is for an arrow from the N–H bond to the N atom Maximum any 3 of 4 marks for the mechanism for wrong organic reactant OR wrong organic product if shown

Award full marks for an SN1 mechanism in which M2 is the attack of the ammonia on

the intermediate carbocation Accept the correct use of “sticks”


(c) M1 (addition) polymerisation OR poly-addition Ignore “additional” Credit polyprop-1-ene and polypropylene

M2 poly(propene) / polypropene Penalise “condensation polymerisation”

2

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(d)

Penalise M1 if covalent KOH

M1 must show an arrow from the lone pair on the oxygen of a negatively charged hydroxide ion to a correct H atom

Penalise M3 for formal charge on C of C–Br or incorrect partial charges on C−Br.

M2 must show an arrow from a correct C–H bond adjacent to the C–Br bond to the appropriate C–C bond. Only award if an arrow is shown attacking the H atom of a correct C−H bond in M1

Ignore other partial charges Penalise once only in any part of the mechanism for a line and two dots to show a bond

M3 is independent provided it is from their original molecule, but CE=0 if nucleophilic substitution

Maximum any 2 of 3 marks for wrong organic reactant

Award full marks for an E1 mechanism in which M3 is on the correct carbocation.

Accept the correct use of “sticks” for the molecule except for the C–H being attacked


[15]

M21. (a) (i) Structure of (Z)-but-2-enenitrile with or without either or both of the CH3 and the

CN groups displayed

Penalise C−NC

Do not penalise C−H3C

Ignore bond angles. 1

(ii) Restricted rotation / no (free) rotation about the double bond / about the C=C OR does not rotate (about the double bond)

Must use the word rotate / rotation. 1

of 39

(b) Repeating unit of polyalkene

All the bonds relevant to the unit must be drawn out including those on either side of the unit. There is no need to expand either the CH

3

or the CN Penalise C−NC

Penalise “sticks”. Ignore brackets. Penalise “n”

1

(c) Feature 1

Absorption / peak in the range 2220 to 2260 cm−1 or specified value in this range or marked correctly on spectrum and (characteristic absorption / peak for) C≡N / CN group / nitrile / cyanide group

Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption.

Allow a peak at 2200 cm−1 to 2220 cm−1 in this case.

Feature 2

Absorption / peak in the range 1620 to 1680 cm−1 or specified value in this range or marked correctly on spectrum and (characteristic absorption / peak for) C=C group / alkene / carbon-carbon double bond

Ignore reference to other absorptions eg C-H Either order.

2 [5]

M22. (a) Structure for 3-methylbut-1-ene

H2C=CHCH(CH

3)

2

Any correct structural representation. Credit “sticks” and require the double bond.

1

(b) Structure for 2-methylpropan-2-ol

(CH3)

3COH

Any correct structural representation. Credit “sticks”.

1

of 39

(c) Structure for propene

H2C=CHCH

3

Any correct structural representation. Credit “sticks” and require the double bond.

1

(d) Structure for 2-aminobutane

CH3CH

2CH(NH

2)CH 3

Any correct structural representation. Credit “sticks”.

1 [4]

M23. (a) M1 concentrated sulfuric acid OR c(onc) H2SO

4

If no reagent or incorrect reagent in M1, CE= 0 and no marks for M2 or M3

M2 (cream solid) turns orange OR orange / red / brown fumes / gas / vapour

If dilute sulfuric acid OR “aq” (alone) CE=0

M3 (yellow solid) turns black OR purple fumes / gas / vapour OR correct reference to H

2S observation (eg bad egg smell)

If H2SO

4 / sulfuric acid given but not stated whether dilute or

concentrated, penalise M1 and mark on for M2 and M3 If incorrect formula for the acid, penalise M1 but mark M2 and M3

OR as an alternative

M1 concentrated ammonia OR c(onc) NH3

If NH3 / ammonia / aq ammonia given, but not stated as

concentrated OR if dilute ammonia given, penalise M1 but mark on for M2 and M3 Ignore “partially” and ignore “clear” in M2

M2 (cream solid) dissolves / solution formed

M3 precipitate remains / does not dissolve / insoluble OR no reaction / no change / (yellow solid) turns to white solid

If incorrect formula for ammonia, penalise M1 but mark M2 and M3 In M3 for ammonia. ignore “nothing (happens)”. ignore “no observation”.

3

of 39

(b) M1 AgNO3 OR silver nitrate OR any soluble silver salt

If no reagent OR incorrect reagent in M1, CE= 0 and no marks for M2 OR M3

M2 white precipitate or white solid / white suspension An insoluble silver salt OR Tollens’ OR Ag OR ammoniacal silver nitrate or HCl / AgNO

3 CE= 0 for the clip.

M3 remains colourless OR no reaction OR no (observed) change OR no precipitate For M1 Credit acidified (OR HNO

3) silver nitrate for M1 and mark on.

If silver ions or incorrect formula for silver nitrate, penalise M1 but mark M2 and M3

Credit alternative test for nitrate ions For M2 Ignore “cloudy solution” OR “suspension”. For M3 Ignore “nothing (happens)”. Ignore “no observation”. Ignore “clear”. Ignore “dissolves”.

3

of 39

(c) M1 Br2 OR bromine (water) OR bromine (in CCl

4 / organic solvent)

If no reagent or incorrect reagent in M1, CE= 0 and no marks for M2 or M3

Either Order M2 (stays) Orange / red / yellow / brown / the same

OR no reaction OR no (observed) change OR reference to colour going to cyclohexane layer

No credit for combustion observations; CE=0 For M2 in every case. Ignore “nothing (happens)”. Ignore “no observation”. Ignore “clear”.

M3 decolourised / goes colourless / loses its colour With bromine (water) For M1, it must be a whole reagent and / or correct formula. If oxidation state given in name, it must be correct. For M1 penalise incorrect formula, but mark M2 and M3

OR as an alternative

Use KMnO4/H

2SO

4

M1 acidified potassium manganate(VII) or KMnO4/H

2SO

4

OR KMnO4/ H+ OR acidified KMnO

4

M2 (stays) purple or no reaction or no (observed) change With potassium manganate(VII) For M1

M3 purple to colourless solution OR goes colourless If “manganate” or “manganate(IV)” or incorrect formula or no acid, penalise M1 but mark M2 and M3

Credit alternative test using iodine (for M1) M2 (brown) to purple or accept no change, M3 colourless Credit alternative test using concentrated H

2 SO

4

M2 no change, M3 brown Credit alkaline / neutral KMnO

4 for possible full marks but M3 gives

brown precipitate or solution goes green. 3

of 39

(d) M1 Tollens’ (reagent) OR ammoniacal silver nitrate OR a description of making Tollens’ (Ignore either AgNO

3 or [Ag(NH

3)2

+] or “the silver mirror test” on their own, but mark

M2 and M3) M2 silver mirror OR black solid / precipitate (Ignore silver precipitate) M3 (stays) colourless or no reaction or no (observed) change

If no reagent or incorrect reagent in M1, CE= 0 and no marks for M2 or M3 For M3 in every case Ignore “nothing (happens)”. Ignore “no observation”.

Alternative using Fehling’s (solution) M1 Fehling’s (solution) or Benedict’s solution

(Ignore Cu2+(aq) or CuSO4 on their own, but mark M2 and M3)

M2 Red solid / precipitate (Credit Orange or brown solid) M3 (stays) blue or no reaction or no (observed) change

With potassium dichromate(VI) For M1 If “dichromate” or “(potassium) dichromate(IV)” or incorrect formula or no acid, penalise M1 but mark M2 and M3

Alternative using K2Cr

2O

7/H

2 SO

4

M1 acidified potassium dichromate or K2Cr

2O

7/H

2SO

4

OR K2Cr

2O

7/H+ OR acidified K

2Cr

2O

7

M2 (Orange to) green solution OR goes green M3 (stays) Orange or no reaction or no (observed) change

For M3 Ignore dichromate described as “yellow” or “red”.

With potassium manganate(VII) For M1 If “manganate” or “(potassium manganate(IV)” or incorrect formula or no acid, penalise M1 but mark M2 and M3

Alternative using KMnO4 /H

2 SO

4

M1 acidified potassium manganate(VII) or KMnO4 /H

2 SO 4

OR KMnO 4 /H + OR acidified KMnO 4

M2 purple to colourless solution OR goes colourless M3 (stays) purple or no reaction or no (observed) change

Credit alkaline / neutral KMnO4 for possible full marks but M2 gives

brown precipitate or solution goes green. 3

[12]

of 39

M24. (a) (i) M1 (Yield) increases / goes up / gets more

If M1 is blank, mark on and seek to credit the correct information in the explanation. If M1 is incorrect CE=0 for the clip.

M2 The (forward) reaction / to the right is exothermic or gives out / releases heat OR The reverse reaction / to the left is endothermic or takes in / absorbs heat M3 depends on a correct statement for M2

M3 depends on correct M2 and must refer to temperature / heat The (position of ) equilibrium shifts / moves left to right to oppose the decrease in temperature For M3, the equilibrium shifts / moves to release heat OR to raise the temperature OR to heat up the reaction.

3

(ii) M1 Concentration(s) (of reactants and products) remain or stay constant / the same

For M1 credit [ ] for concentration.

M2 Forward rate = reverse / backward rate Not “equal concentrations”. Not “concentrations is / are the same”. Not “amount”. Ignore “dynamic” and ignore “speed”. Ignore “closed system”. It is possible to score both marks under the heading of a single feature.

2

(b) KBr + H2SO

4 KHSO

4 + HBr

Credit this equation in its ionic form. Ignore state symbols. Credit multiples.

1

of 39

(c) M1 SO2 identified

M2 correctly balanced equation (would also gain M1) Credit M2 equation in its ionic form. Ignore state symbols.

2HBr + H2SO

4 Br

2 + SO

2 + 2H

2O

Credit multiples. Not H

2SO

3 on the right-hand side.

Mark M3 independently M3 Oxidising agent OR electron acceptor OR oxidant OR to oxidise the bromide (ion) / HBr

M3 Not “electron pair acceptor”. 3

of 39

(d) (i) M1 Electrophilic addition

M1 both words required. For the mechanism M3 Penalise incorrect partial charges on O − H bond and penalise formal charges Ignore partial negative charge on the double bond.

M5 Not HSO4

–

For M5, credit as shown or −:OSO3H ONLY with the negative

charge anywhere on this ion OR correctly drawn out with the negative charge placed correctly on oxygen.

M2 must show an arrow from the double bond towards the H atom of the H − O bond / HO on a compound with molecular formula for H

2SO

4

M2 could be to an H+ ion and M3 an independent O − H bond break on a compound with molecular formula for H

2SO

4

Max any 3 of 4 marks for a correct mechanism using the wrong organic reactant or wrong organic product (if shown) or a primary carbocation.

M3 must show the breaking of the O − H bond on H2SO

4

Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M5 must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards the positively charged carbon atom on their carbocation

Credit the correct use of “sticks”. For M5, credit attack on a partially positively charged carbocation structure, but penalise M4


(ii) Hydrolysis Credit “(nucleophilic) substitution” but do not accept any other prefix. Credit phonetic spelling.

1

(iii) Catalyst 1

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