A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF...

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TOPIC 23 ANSWERS & MARK SCHEMES A2 Level QUESTIONSHEET 1 E/Z (CIS/TRANS) ISOMERISM a) Explanation Restricted rotation (1) of atoms or groups about a C=C bond / when C atoms are joined together by a double bond (1) (Do not allow restricted rotation of molecules.) Due to the π- bond locking atoms in position (1) Structures and names Z-pent-2-ene or (cis pent-2-ene) (1) E-pent-2-ene or (trans pent-2-ene) (1) b) Suggestion Alicyclic ring prevents rotation / locks the molecule in position (1) Structures c) CH 2 =CHCH 2 CH 3 No (1) (CH 3 ) 2 C=CH 2 No (1) CHCl=CHCl Yes (1) CHCl=CHCH 3 Yes (1) CHCl=CClCH 3 Yes (1) CH 3 CH=CClCH 2 CH 3 Yes (1) Structural feature Both C atoms of the C=C bond must be joined to different atoms or groups (1) C C C C CH 3 CH 3 CH 2 H H CH 3 CH 2 CH 3 H H (1) (1) (1) Cl Cl Cl Cl (1)

Transcript of A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF...

Page 1: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 1

E/Z (CIS/TRANS) ISOMERISM

a) Explanation Restricted rotation (1)of atoms or groups about a C=C bond / when C atoms are joined together by a double bond (1)(Do not allow restricted rotation of molecules.)Due to the π- bond locking atoms in position (1)

Structures and names

Z-pent-2-ene or (cis pent-2-ene) (1) E-pent-2-ene or (trans pent-2-ene) (1)

b) Suggestion Alicyclic ring prevents rotation / locks the molecule in position (1)

Structures

c) CH2=CHCH

2CH

3No (1)

(CH3)

2C=CH

2No (1)

CHCl=CHCl Yes (1)CHCl=CHCH

3Yes (1)

CHCl=CClCH3

Yes (1)CH

3CH=CClCH

2CH

3Yes (1)

Structural feature Both C atoms of the C=C bond must be joined to different atoms or groups (1)

C CC CCH

3CH

3CH

2

H H

CH3CH

2

CH3

H

H(1)

(1)

(1)

Cl Cl

Cl

Cl

(1)

Page 2: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 2

OPTICAL ISOMERISM

a) (i) Structures

(Tapered bonds (or similar) to show tetrahedral distribution about C are essential)

Means of distinguish between them Equal rotation (1)of the plane of polarised light (1)but in opposite directions (1)

(ii) Butan-2-ol has a chiral centre / asymmetric carbon atom (1)but butanone does not (1)

b) (i) Isomers whose molecules bear an object to mirror image relationship (1)

(ii) No effect on the plane of polarised light / optically inactive (1)

(iii) Racemic mixture / racemate (1)

(iv) Ethanal is trigonal planar about the carbonyl C atom (1)There is an equal probability / 50:50 chance of CN- attacking from above and below the plane (1)so that equal amounts of the mirror image ions are formed (1)

This leads to (±)-CH3CH(OH)CN / dl-CH

3CH(OH)CN (1)

Or to (±)-lactic acid / dl-lactic acid (1)Maximum 4 marks

C

CH3

C2H

5

OHHC

CH3

C2H

5

HO H

(1) (1)

C

CH3

CN

O -

HC

CH3

NC

- O H(1)

c)

H C HC C C C

H

H

HH

H H

O

H

C

H

HH

CH3

CH3

CH2

CH C

O

O H

NH2

C

H

C N H

OH

H H

CH3

HO

HO

CH2C

CH3

CH3CH

2

CH2

C CH3

H

NH2 H C C

CH2OH

N

CH2Cl

CH3CH3

C O CH2

CH2

CH CH3

O CH3

CHCl

CH2

C O

CH2

CH2

CH2

* *

* * *

*

1 mark per correctly placed * and - ½ per wrongly placed *.

d) Only one of the isomers is beneficial (1)So half the dose needed if single isomer used (1)The other isomer may have unpleasant side effects (1)

Page 3: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 3

TEST QUESTION ON ISOMERISM

a) (i) Skeletal isomerism CH3CH

2CH

2CH

2OH / CH

3CH(OH)CH

2CH

3 (1)

and (CH3)

2CHCH

2OH / (CH

3)

3COH (1)

Positional isomerism CH3CH

2CH

2CH

2OH (1) and CH

3CH(OH)CH

2CH

3 (1)

Or (CH3)

2CHCH

2OH (1) and (CH

3)

3COH (1)

Functional group isomerism Accept any of the C4 alcohols (1) and any of the C

4 ethers (1)

Stereoisomerism

(ii) Butan-2-ol has a chiral centre / asymmetric C atom (1)∴ can exhibit optical isomerism / exist in two non-superimposable forms (1)but none of the compounds has a C = C bond (or other structural feature) which can cause restricted rotationof atoms (1)∴there is no possibility of geometrical isomerism / existence of cis and trans isomers (1)

b) (i) Geometrical / cis-trans isomerism (1)

(ii)

C

CH3

C2H

5

OHHC

CH3

C2H

5

HO H(1) and (1)

(iii) Melting point / solubility (1)

CH3 CH2

C=N

CH3

.N

H

C6H5 (1)

CH3 CH2

C=N

CH3

..

NH

C6H5

(1).

Page 4: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 4

STRUCTURE OF BENZENE

a) (i) Platinum catalyst, room temperature / nickel catalyst, heat (1)

(ii)

(iii) Since three double bonds are hydrogenated, ∆H = 3(-120) = -360 kJ mol-1 (1)

(iv) Benzene is more stable than expected (1)by (360 – 208) = 152 kJ mol-1 (1)This is because benzene contains a delocalised system of electrons (1)

b) (i) Delocalised Electrons are not restricted to “2-electron, 2-centre” bonds (1)but are dispersed / spread / mobile over a greater number of nuclear centres (1)

Unsaturated One or more (carbon-carbon) bonds are multiple bonds / the compound will undergo an additionreaction with hydrogen (1)

(ii)

X

X

(1)

(iii) Benzene does not undergo electrophilic addition reactions (1)

(1)

and

X

X(1)Benzene does not produce disubstituted isomers of the form

Electron-diffraction measurements show that all the carbon-carbon bonds are of equal length / intermediatebetween C-C and C=C (1)The enthalpy of hydrogenation of benzene is less exothermic than expected (1)The enthalpy of formation of benzene is less endothermic than expected (1)Maximum 3 marks

Page 5: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 5

STRUCTURES OF CYLOALKENES

a) Alkene I Cyclohexene (1)Alkene II 1,3-Cyclohexadiene (1)Alkene III 1,4-Cyclohexadiene (1)

b) + H

2 → (1)

+ 2H2 → (1)

c) If the π-orbitals of II were completely localised / by comparison with cyclohexene (1)enthalpy of hydrogenation of II could be calculated as –119.6 x 2 = -239.2 kJ mol-1 (1)This is 7.5 kJ mol-1 different from the experimental value (1)∴II is energetically more stable than if it had two completely localised π-bonds (1)A slight degree of delocalisation of π-electrons must be occurring (1)Maximum 4 marks

d) Shortest bonds will be a and c (1)Longest bonds will be d, e and f (1)b will be slightly shorter than d, e, and f (1)because of the slight degree of delocalisation (1)

e) Estimate -239.2 kJ mol-1 (1)

Reasons π-bonds are too far apart to overlap (1)No delocalisation of π-electrons (1)∴ no increase in stability (1)

Page 6: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 6

BOND TYPE AND REACTIVITY

a) (i) Electrophiles are attracted by electrons of the π-bond (1)The π-bond is weak / easily broken (1)

(ii) C⎯H bonds are little polarised / C and H have similar electronegativity (1)For an alkane to react, strong σ-bonds would have to be broken (1)

b) (i) Polarisation of the bond / Cδ+ ⎯Xδ- (1)due to the high electronegativity of halogens compared with carbon (1)

(ii) RCl < RBr < RI (1)

(iii) Bond strength decreases from C⎯Cl to C⎯I (1)hence a halide ion can leave more readily (1)This outweighs the decreasing strength of the –I effect / the lower electronegativity of the halogens (1)Maximum 2 marks

c) (i) Nucleophilic reagents / nucleophiles (1)

(ii) Bond polarisation Cδ+ Oδ- / oxygen is much more electronegative than carbon (1)The π-bond is easily polarised (1)

(iii) The π-bond is weak / easily broken (1)but the σ-bond is strong (1)

(iv) They are repelled by the π-electrons of the C C bond (1)

(v) HCN would have to undergo heterolytic fission / dissociation (to H+ and CN-) (1)This is difficult because HCN is a very weak acid / because of the strength of the H⎯CN bond (1)

⎯⎯

⎯⎯

Page 7: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 7

(ii) Aluminium chloride / iron (III) chloride (1)

(iii) Electrophilic (½) substitution (½)

(iv) Heterolytic fission / heterolysis (1)

c) Example CH3CH

2Br CH

3CH

2OH (1)

Nucleophilic substitution (1)

CH3CH

2Br CH

2 = CH

2 (1)

Elimination (1)

REACTION CONDITIONS AND PRODUCT

a) (i) Free radical (½) substitution (½)

(ii) Homolytic fission / homolysis (1)

(iii) Stage 1

Ethanolic / alcoholic NaOH(1)

Aqueous NaOH (1)

Cl Cl.. 2Cl

.(1)

CH3

+ Cl.

+ HCl (1)

Stage 2

.CH

2

+ Cl2

CH2Cl

+ HCl (1)

.CH

2

Stage 3

+ Cl.

(1)

.CH

2 CH2Cl

Or 2Cl.

Cl2

Or .CH

2 CH2 CH

2(1)

b) (i) CH3

+ Cl2

CH3

+ HCl (1)Cl

Or

CH3

+ Cl2

CH3

+ HCl (1)

Cl

(1)

2

Page 8: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 8

NITRATION OF ARENES

a) Reagents Concentrated nitric acid (1)and concentrated sulfuric acid (1)

Conditions 50 - 60 °C (1)

Equation + HNO

3 → + H

2O (1)

Or C6H

6 + HNO

3 → C

6H

5NO

2 + H

2O (1)

b) (i) Lower temperature / 30 - 40 °C (1)

(ii) Use fuming nitric acid / more concentrated nitric acid (1)and a higher temperature (1)

(iii) Formula

(1)

Use High explosive (1)

c) (i) C6H

5NO

2 + 6[H] → C

6H

5NH

2 + 2H

2O (1)

Or + 6[H] → + 2H2O (1)

(ii) Reduction(1)

(iii) Tin (1) and concentrated hydrochloric acid (1)(Accept HCl (aq) but not just ‘HCl’.)

(iv) Primary aromatic amines form the basis of the azo dyestuffs industry (1)

NO2

CH3

NO2

NO2

O2N

NO2

NH2

Page 9: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 9

HALOGENATION OF ARENES

a) (i) Conditions Br2 in solution (in a named solvent) (1)

Room temperature / 20 °C (1)

Equation + Br2 → (1)

Or with molecular formulae in place of the structural formulae

(ii) (Electrophilic) addition (1)

b) (i) Conditions Br2 + AlBr

3 / Al catalyst (1) (Allow AlCl

3)

Room temperature / 20 °C (1)

Equation + Br2 →

+ HBr (1)

Or with molecular formulae in place of the structural formulae

(ii) (Electrophilic) substitution (1)

c) π-electrons in cyclohexene are localised between two adjacent C atoms (1)π-electrons in benzene are delocalised over the six-membered ring (1)Therefore π-electrons in benzene attract bromine / the reagent / the electrophile less strongly (1)

BrBr

Br

Page 10: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 10

ALKYLATION AND ACYLATION OF ARENES

a) (i) Reagent Chloromethane / bromomethane / iodomethane (1)

Conditions AlCl3 catalyst (1)

Room temperature / 20 °C (1)

Equation + CH3Cl → + HCl (1)

Or C6H

6 + CH

3Cl → C

6H

5CH

3 + HCl (1)

(ii) It is difficult to prevent further alkylation / a dimethylbenzene or trimethylbenzene is formed readily (1)

(iii) Type of reaction Oxidation (1)

Reagent KMnO4 (½) + NaOH(aq) (½)

Or K2Cr

2O

7 (½) + dil. H

2SO

4 (½)

Or dilute HNO3 (1)

b) (i) Conditions AlCl3 catalyst (1)

50 ºC / heat (1)

Equation + CH3COCl → + HCl (1)

Or C6H

6 + CH

3COCl → C

6H

5COCH

3 + HCl (1)

Name of product Phenylethanone / acetophenone (1)

(ii) Type of reaction Reduction (1)

Reagent NaBH4 / Zn + dil. H

2SO

4 / other named combination of metal and protic solvent (1)

CH3

COCH3

Page 11: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 11

PHENOL

a) Identity of phenols I, II, & IV (1) (All must be correct)Basis of identification A phenol must have at least one –OH group attached directly to a benzene ring (1)

b) (i) Identity of A Sodium phenoxide / sodium phenate / C6H

5O Na (1)

Identity of B Mainly phenol / (saturated) solution of water in phenol (1)(Allow just ‘phenol’)

Equations

Or C6H

5OH + NaOH → C

6H

5O Na + H

2O (1)

Or C6H

5O Na + HCl → C

6H

5OH + NaCl (1)

(ii) Reason 1 Lone pair of electrons on O (1)is drawn towards the benzene ring (1)O⎯H bond is weakened / increasingly polarised (1)so that H+ is lost relatively easily (1)Maximum 3 marks

Reason 2 The phenoxide ion / C6H

5O is stabilised (1)

by delocalisation of –ve charge (1)over O and the benzene ring (1)This encourages dissociation / ionisation / formation of C

6H

5O (1)

No scope for delocalisation in an alkoxide ion / corresponding anion from an alcohol (1)Maximum 3 marks

c) (i) White (½) precipitate (½)

(ii)

+ 3Br2 → + 3HBr (1)

(iii) Lone pair of electrons on O (1)is drawn towards the benzene ring / occupies a p-orbital which overlaps the delocalised π-orbital of the ring (1)Hence electron density on the ring is increased (1)and the ring is activated towards electrophiles / electrophiles are more strongly attracted (1)Maximum 3 marks

d) Antiseptics / disinfectants (1)

+

-

OH

+ NaOH → + H2O (1)

O Na

-

+

-

+

-

O Na

+

+ HCl → + NaCl (1)

OH

-

+

-

-

OH OH

Br

BrBr

Page 12: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 12

ALDEHYDES AND KETONES

a) (i) C (½) Butanone / butan-2-one (½)

(ii) A (½) Propanal (½) andB (½) 2-methylpropanal (½)

(iii) C (½) Butanone (½)Allow if named in (i)

b) (i) Silver mirror (1)

(ii) propanoic acid (1)

(iii) Fehlings (1) Red precipitate (1)or Potassium dichromate (VI) (1) orange to green (1)or potassium manganate(VII) (1) purple to colourless (1)

c) (i) LiALH4 or NaBH

4 (1)

(ii) In dry ether (1) for LiALH4

or in solution in water or methanol for NaBH4 (1)

Page 13: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 13

USE OF 2,4 - DINITROPHENYLHYDRAZINE

a) C H OMoles 69.8/12 11.6/1 18.6/16

5.817 11.6 1.163 mol % (1)Ratio 5 10 1 (1)

Empirical formula is C5H

10O ; relative formula mass = 86 = relative molecular mass (1)

therefore molecular formula is also C5H10O (1)

b) Aldehydes: CH3CH

2CH

2CH

2CHO

CH3CH

2CH(CH

3)CHO

CH3CH(CH

3)CH

2CHO

CH3C(CH

3)

2CHO

Ketones: CH3COCH

2CH

2CH

3

CH3CH

2COCH

2CH

3

CH3COCH(CH

3)

2 (1 mark each)

c)

+ H2N ⎯ NHC O

NO2

NO2

N ⎯ NHC

NO2

NO2

(2) Delete 1 mark for each error+ H2O

d) Test Tollens’ reagent / ammoniacal silver nitrate (1)Or Fehling’s solution (1)

Conditions Warm (not boil) for Tollens’ reagent (1)Or boil / heat for Fehling’s solution (1)

Observation with aldehydes Silver mirror (1)Or red / brown precipitate for Fehling’s solution (1)

Observation with ketones No silver mirror (1)Or no red / brown precipitate / solution remains dark blue for Fehling’s solution (1)

e) (i) Compare the melting point with that obtained from a data source (1)

(ii) Recrystallise (1) to make the compound pure (1),because impurities change/ lower the melting point. (1)

Page 14: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 14

THE TRIIODOMETHANE REACTION

a) (i) Yellow (½) precipitate (½)

(ii) CH3CHO + 3I

2 + 3NaOH → CI

3CHO + 3NaI + 3H

2O (1)

CI3CHO + NaOH → CHI

3 + HCOO- Na+ (1)

(iii) CHI3 is hydrolysed / decomposed by the NaOH (1)

(iv) NaClO / ClO- oxidises (1)KI / I- to I

2 (1)

b) (i) I2 & NaOH oxidises (1)

CH3CHOH to CH

3CO (1)

(ii) less reactive/ (1)

c) A, E, F, G (1 each)

Page 15: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 15

GRIGNARD REAGENTS

a) Preparation Magnesium (½) and iodomethane / methyl iodide (½)in dry (½) ether (½) under reflux condenser (½)with iodine (½) as a catalyst (½)Maximum 3 marks

Equation CH3I + Mg → CH

3MgI (1)

b) (i) Reagent: methanal (1)

Intermediate: CH3−CH

2OMgl (1)

Conditions for second stage: Acidic hydolysis (1)

(ii) Reagent: Solid (1) carbon dioxide (1) (Allow ‘Drikold’ or ‘dry ice’ for both marks)

Intermediate:

Conditions for second stage Acidic hydolysis (1)

c) A = propanalB = propanoneC = butan-2-olD = 2-methylpropan-2-ol(Award 1 mark for name or formula in each case )

Peak at m/z 29 due to CH3CH

2+ / C

2H

5+ (1)

Peak at m/z 30 due to CH(OH)+ (1) Not CH2O+

(Deduct 1 mark if +ve charges are missing)

CH3C

OMgI

O(1)

Page 16: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 16

CARBOXYLIC ACIDS I

a) (i) Product: Potassium ethanoate (1)

Type of reaction: Acid-base / neutralisation (1)

Equation: CH3COOH + KOH → CH

3COOK + H

2O (1)

(ii) Product: Magnesium ethanoate (1)

Type of reaction: Acid-base / neutralisation (1)

Equation: CH3COOH + MgO → CH

3COO)

2Mg + H

2O (1)

b) (i) Reagent: Na2CO

3(aq) / NaHCO

3(aq) (1)

Observation: Effervescence / gas evolved which turns limewater milky (1)

Equation: 2RCOOH + Na2CO

3 → 2RCOO− Na+ + H

2O + CO

2 (1)

Or RCOOH + NaHCO3 → RCOO− Na+ + H

2O + CO

2 (1)

Or similar alternatives

c) Reagents Ethanoic acid (1)Butan-1-ol (1)Concentrated sulfuric acid (1)

Conditions Heat / boil under reflux (1)

Equation CH3COOH + CH

3CH

2CH

2CH

2OH ¾ CH

3COOCH

2CH

2CH

2CH

3 + H

2O (1)

Type of reaction Esterification / addition-elimination / condensation (1)

Page 17: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 17

CARBOXYLIC ACIDS II

a) (i) Polarisation of the C=O bond (1)increases polarisation of the O⎯H bond / weakens the O⎯H bond (1)so that there is a greater degree of dissociation / [H+] is increased (1)

(ii) -I effect / electron - withdrawing effect / high electronegativity of Cl atoms (1)further increases polarisation of / weakens the O⎯H bond (1)so that degree of dissociation / [H+] is increased (1)Also, the anion CCl

3COO- is stabilised (1)

by delocalisation of –ve charge (1)Maximum 4 marks

b) (i) Reagent PCl5 / PCl

3 / SOCl

2 (1)

Equation CH3CH

2COOH + PCl

5 → CH

3CH

2COCl + POCl

3 + HCl (1)

Or 3CH3CH

2COOH + PCl

3 → 3CH

3CH

2COCl + H

3PO

3 (1)

Or 3CH3CH

2COOH + SOCl

2 → CH

3CH

2COCl + SO

2 + HCl (1)

(ii) Reagent Conc. NH3(aq) (1) Accept just ‘NH

3’

Equation CH3CH

2COCl + NH

3 → CH

3CH

2CONH

2 + HCl (1)

c) (i) Description Effervescence (1)Gas turns limewater milky (1)at room temperature (1)Maximum 2 marks

Formula of product

(ii) Description Reaction on heating (1)with conc. H

2SO

4 (1)

to give a fruity smell (1)Maximum 2 marks

Formula of product

COO Na

COO Na

COOCH3

COOCH3

(1)

(1) Ionic charges must be shown

d) Benzene-1,4-dicarboxylic acid (1)Hydrogen bonding can lead to the formation of “long-chains” of molecules (1)but in benzene-1,2-dicarboxylic acid hydrogen bonding is largely intramolecular (1)

+

+

-

-

Page 18: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 18

ACYL CHLORIDES

a) Name Propanoyl chloride (1)

Two advantages Better yield / reaction goes to completion / an equilibrium mixture is not obtained (1)Faster reaction (1)

Two disadvantages Acyl chlorides are relatively expensive (1)Fumes of hydrogen chloride / toxic fumes (1)

b) (i) Acyl chloride Benzenecarbonyl chloride / benzoyl chloride (1)

Reagent Aqueous ammonia (1)

(ii) Addition-elimination / condensation (1)

(iii) Problem (White) smoke of ammonium chloride (1)

Origin Reaction between HCl (formed in the main reaction) and unreacted NH3 (1)

Precaution Carry out the experiment in a fume cupboard (1)(Allow ‘limited ammonia’)

c) (i) Mix / react ethanoyl chloride and the amine at room temperature (1)Recrystallise the product (1)Determine its melting point (1)Compare this m.p. with that in a data book / textbook (1)Maximum 3 marks

(ii) Equation CH3COCl + C

2H

5NH

2 → CH

3CONHC

2H

5 + HCl (1)

Name N-ethylethanamide (1)

Page 19: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 19

ESTERS

a) O O OH – C H – C CH

3 – C

OCH2CH

2CH

3 OCH(CH

3)

2 OCH

2CH

3

Propyl methanoate Isopropyl methanoate Ethyl ethanoateor 1-methylethyl methanoate

OCH

3CH

2– C

OCH3

Methyl propanoate

Award (1) for each formula and (1) for each name if correctly related to formulaMaximum 6 marks

b) (i) Compound II is CH2OH

CH2OH (1)

Compound III is CH3CH

2CH

2COOH (1)

(ii) Compound I Ester (1)

Compound II Alcohol / diol (1)

Compound III Carboxylic acid (1)

(iii) Hydrolysis / saponification (1)

(iv) Alkaline hydrolysis goes to completion (1)Acidic hydrolysis is reversible / results in an equilibrium mixture (1)∴ yield is higher from alkaline hydrolysis (1)Maximum 2 marks

c) Perfumes (1)Solvents / thinners (1)Food flavourings (1)Plasticisers (1)Maximum 3 marks

Page 20: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 20

NITRILES

a) n (NaOH) = 0.1 × 16.65/1000 = 1.665 × 10-3 mol (1)∴ n (H) = 1.665 × 10-3 mol in 25.0 cm3

= 1.665 × 10-2 mol in 250 cm3 (1)∴ M

r (H) = 1/1.665 × 10-2 = 60.06 / 60 (1)

b) If formula of H is R-COOH, Mr of (R-) is 60.06 – (12 + 32 + 1) = 15.06 (1)

∴ R- is CH3- (1)

∴ H is ethanoic acid / CH3COOH (1)

and G must be ethanenitrile / CH3CN (1)

c) (i) CH3CN + NaOH + H

2O → CH

3COO-Na+ + NH

3 (1)

(ii) CH3COO-Na+ + H

2SO

4 → CH

3COOH + NaHSO

4 (1)

d) Mr (CH

3CN) = (15 + 12 + 14) = 41 and M

r (CH

3COOH) = 60

4.0 g CH3CN ≡ 4.0 / 41 mol (1)

∴ theoretical yield of H is 60(4.0) / 41 = 5.85 g (1)% yield is 4.5(100) / 5.85 = 76.9% / 77% (1)

e) Reducing agent LiAlH4 / H

2 / Zn + dil H

2SO

4 (1)

Conditions For LiAlH4, dry ether (1)

For H2, Pt / Ni catalyst (1)

For Zn + dil. H2SO

4, heat / boil (1)

Equation CH3C≡N + 4[H] → CH

3CH

2NH

2 (1)

Or CH3C≡N + 2H

2 → CH

3CH

2NH

2 (1) only if H

2 is quoted as the reducing agent

Or CH3C≡N + 2Zn + 2H

2SO

4 → CH

3CH

2NH

2 + 2ZnSO

4 (1)

Page 21: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 21

AMIDES

a) Heat / boil (1)with bromine (1)and alkali / NaOH(aq) (1)

b) (i) Ethanenitrile (1)CH

3CN (1)

(ii) Heat / distil (1)with P

4O

10 (1)

(iii) Elimination (of water) / dehydration (1)

c) Smelly compound in Solution A Ethanoic acid (1)

Compound in Solution B Sodium ethanoate (1)

Gas C Ammonia (1)

(Accept formulae in lieu of names)

d) (i) Peptide link (1)

(ii) Nylon (1)

(iii) Protein (1) (Allow ‘polypeptide’)

Page 22: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 22

AMINES

a) (i) CH3NH

2 + H

2O ž CH

3NH

3 + OH (1)

(ii) The high concentration of OH ions from the NaOH (1)disturbs equilibrium to the left hand side (1)to give molecules of CH

3NH

2, which is a gas (1)

Maximum 2 marks

b) Name of A Phenylammonium chloride (1)

Name of B Phenylamine (1)

Equation 1 C6H

5NH

2 + HCl → C

6H

5NH

3 Cl (1)

Equation 2 C6H

5NH

3 Cl + NaOH → C

6H

5NH

2 + NaCl (1)

c) (i) Strength compared with ammonia Stronger (1)

Reasons Electron releasing effect / +I effect of C2H

5 group (1)

increases electron availability on the N atom (1)

so that a lone pair of electrons on N is donated more readily (1)

and a proton / H is more strongly accepted (1)

Maximum 3 marks

(ii) Strength compared with ammonia Weaker (1)

Reasons Lone pair of electrons on N is drawn towards the benzene ring (1)

so that electron availability on the N is reduced (1)

Donation of the lone pair occurs less readily (1)

and a proton / H is less strongly attracted (1)

Maximum 3 marks

d) (i) Substitution / replacement of H on the N atom (1)by an acyl group / RCO (1)

(ii) Ethanoyl chloride / ethanoic anhydride / benzenecarbonyl chloride (1)

(iii) N-substituted amide / substituted amide / amide (1)

(iv) Mark consequentially from (ii), e.g.

CH3COCl + C

6H

5NH

2 → CH

3CONHC

6H

5 + HCl (1)

Accept C6H

5NHCOCH

3

+

-

-

+

-

+

-

+

+

Page 23: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 23

DIAZOTISATION

a) (i) Treatment of a primary aromatic amine with nitrous acid to form a diazonium salt (1)

(ii) Compounds needed for diazotisation Sodium nitrite (1) and hydrochloric acid (1)

Name of product Benzenediazonium chloride (1)

Equation C6H

5NH

2 + NaNO

2 + 2HCl → C

6H

5N≡N Cl + NaCl + 2H

2O (1)

(iii) Optimum temperature 0-10 0C (1)

Problem if the temperature were too high Hydrolysis of benzenediazonium chloride (1)to give phenol (1)

or decomposition of benzenediazonium chloride (1)to give chlorobenzene (1)

Problem if the temperature were too low Slow / low rate of reaction (1)

b) (i) Conditions Cold / ∼ 5 0C (1)In alkaline solution / NaOH(aq) (1)

Observation Red (½) precipitate (½)

Equation

(ii) Coupling (1)

c) A would give a red precipitate (1)but B would not (1)

+

-

OH+

N≡N ClOH

N=N

+ HCl (1)

-

+

(1) (1)

Page 24: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 24

AMINO ACIDS

a) R

H2N –C – COOH (1)

H

b) Glycine forms zwitterions (1)

NH3 – CH

2 – COO (1)

Attraction between zwitterions is stronger (1)than hydrogen bonding between molecules of glycollic acid (1)

c) (i) Equation (low pH) H2N – R – COOH + H ž H

3N – R – COOH (1)

Equation (high pH) H2N – R – COOH + OH ž H

2N – R – COO + H

2O (1)

(ii) Amino acids exists as zwitterions (1)which are attracted equally strongly to both electrodes (1)

d) (i) CH3

CH2OH CH

3 CH

2OH

H2N – CH – COOH + H

2N – CH – COOH → H

2N – CH – CONH – CH – COOH (1)

CH2OH CH

3 CH

2OH CH

3

H2N – CH – COOH + H

2N – CH – COOH → H

2N – CH – CONH – CH – COOH (1)

(ii) They are amino acids because they both contain –NH2 and –COOH groups (1)

but they are not α-amino acids because these groups are attached to different carbon atoms (1)

+

-

+

+

-

-

Page 25: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 25

PROTEINS

a) (i) Name Peptide link (1) O H

Formula – C – N – (1)

(ii) Condensation polymerisation (1)

(iii) Amino acid residues can be in different sequences (1)

(iv) Protein molecules contain > 30 – 40 amino acid residues / polypeptides contain < 30 – 40 (1)Protein molecules are always hydrated / polypeptides are not hydrated (1)Maximum 1 mark

b) Hydrogen bonding holds a protein chain in a coil or spiral / α-helix (1)Water molecules are held to a protein chain by hydrogen bonding (1)

c) (i) Hydrolysis (1)Heat / boil under reflux (1)with concentrated aqueous acid / hydrochloric acid (1)

(ii) Chromatography (1)

d) They undergo hydrolysis (1)due to the catalytic action of digestive enzymes (1)

Page 26: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 26

TEST QUESTION 1CARBONYL COMPOUNDS

a) C19

H28

O2

b) (i) Red/yellow/orange precipitate (1)

(ii) Orange to green (1)

(iii) Orange/brown to colourless or decolourised (1)

c)

CH3

OH

CH3

HO

1 mark for the HO group and 1 mark for the rest of the molecule.

d)CH

3O

CH3

O

1 mark for the C = O group and 1 mark for the rest of the molecule.

e) (1)

f) (i) B (1)

(ii) A (1)

O

OH

Page 27: A2 23 Ans · 2020. 9. 8. · A2 Level TOPIC 23 ANSWERS & MARK SCHEMES QUESTIONSHEET 5 STRUCTURES OF CYLOALKENES a) Alkene I Cyclohexene (1) Alkene II 1,3-Cyclohexadiene (1) Alkene

TOPIC 23 ANSWERS & MARK SCHEMESA2 Level

QUESTIONSHEET 27

TEST QUESTION 1IPHENOLS

a) Ketone (1)

b) C14

H8O

4 (1)

c) C7H

4O

2 (1)

d) (i) O− Na+

O

O

O− Na+

1 mark for both Na+ ions and 1 mark for the rest of the compound

(ii) The compound is ionic (1) and attracts water molecules (1), but quinizarin is non-polar and does not attract watermolecules (1)

e)

H O CH

Br

Br Br Br

CH2

1 mark for the addition of Br and 1 mark for the substitution of Br