AQA CHEM4 A2 Chemistry - 9 June 2014 Unofficial mark scheme

Very last question was the isomer ones.

Molecular formula: C5H8O2

Draw the structures of

I. Methyl 2-methylpentanoate
Ii. Carboxylic acid that is branched that shows no optical activity
Iii. Carboxylic acid that shows optical activity
Iv. (Can't remember this one)
V. Cyclic structure that has one ketone group and has 2 peaks in its 1H n.m.r

Very last question was the isomer ones.

Molecular formula: C5H8O2

Draw the structures of

I. Methyl 2-methylpentenoate
Ii. Carboxylic acid that is branched that shows no optical activity
Iii. Carboxylic acid that shows optical activity
Iv. (Can't remember this one)
V. Cyclic structure that has one ketone group and has 2 peaks in its 1H n.m.r

The 2nd Isomer it was an ester that exhibited E-Z stereoisomerism.

new rate 8.3x10^-6 (1) why was it this? Changing the volume changes the pressure therefore doesn't effect k? So i put down the same answer 5.05. Doesn't only temp effect value of k

Hi there, We'll go ahead and create the unofficial mark scheme, just post the answers and the most agreed ones shall be updated for it.

Please Correct any wrong answers and good luck with the rest of your exams.

If anyone can remember the question numbers and which questions were under which number, that would be great thanks.
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Moles of reactants at eqbm 1.6 and 0.2 (2)
Write a KC expression [G]^2/[E] x [F]^2 (1)
Kc units mol^-1 dm^+3 (1)
Kc value 0.30 (3)
How does G conc change if vol increases, G decreases equ moves to left to raise pressure (3)
T1 was higher than T2, exothermic eq to right to oppose temp decrease (3)
What is weak acid slightly dissociated (1)
PH of Caoh2 12.38 (3 or 4)
Mass of carboxy salt 1.09g (5)
pH acid 3.06 (3)
Ka expression (1)
equation of carboxylic acid with Na2CO3 gives salt, water and CO2 (1)
CO2 in air (1) Aqueous CO2 is acidic, H+ react with OH-, less OH-. (3)
Order A 2, Order B 0 (2)
k constant is 5.05 (3)
new rate 8.3x10^-6 (1)

Nucleophillic addition
Mechanism: CN- , lone pair arrow to carbon, one bond from C=O dissociates to C-O- with a lone pair, positive hydrogen, arrow from O lone pair to hydrogen.
Distinguish enantiomers: Each rotates a plane of polarised light, one shall do so clockwise, the other anti clockwise, they rotate in opposite directions.
Why is reaction slow with HCN? Low Ka, low amount of dissociation, so low amount of CN- available to react.


IM force in kevlr is h bond (1)
NH3 lone pair repelled by benzene ring (2)
Mech is electrophilic sub with con hno3 and h2so4 reacting to make NO2+ (6) Sn and HCl reducing NO2 (1)

nucl add elim with OH attacking cocl carbon a was 20-50ppm and carbon b was 60-90ppm (7)
repeating unit of this was straight chain polyester ? (1)
it was condensation polymer (1)
use Br2/bromine water, benzene no reaction decolourises (Red-Brown to Colourless) with cyclohexene (3)
ester 1 was the spectrum, 4.1ppm was ch2 with 3 h on adjacent c, next to O-C=O so shifted downfield, other quartet had 2.1-2.6ppm (4)
quaternary ammonium (bromide) salt, nucl sub with CH3Br in excess (4)
use tollens, nothing with J, K silver mirror, J has 2 peaks K has 4 (5)

Final Question: Isomers of C5H8O2
L. Methyl 2-methylpentanoate
M. Carboxylic acid that is branched that shows no optical activity
N. Carboxylic acid that shows optical activity
O. (Can't remember this one)
P. Cyclic structure that has one ketone group and has 2 peaks in its 1H n.m.r.: The structure was 5 carbons and an oxygen forming a cyclic ring, and the C=O group being on the carbon opposite the O.

Change in volume = change in conc = change in rate

new rate 8.3x10^-6 (1) why was it this? Changing the volume changes the pressure therefore doesn't effect k? So i put down the same answer 5.05. Doesn't only temp effect value of k

even so, the value of k only varies with temp