AQA A Level Chemistry Paper 2 11th June Unofficial Markscheme

Isn’t % yield 26.8%?

Isn’t % yield 26.8%?

Isn’t % yield 26.8%?

Equation 1,6-dibromohexane and excess ammonia

C6H12Br2 2 NH3 —-> C6H16N2 2 HBr

Nucleophilic substitution skeletal formula with ammonia
Cyclic compound by-product
The NH3 of one end comes around and replaces the Br at the other end

Ester formed:
Ethyl propanoate

Explain the term Complementary
Dna strands have complementary base pair shapes which allow for hydrogen bonds between them

Draw hydrogen bonds between the strands
3 bonds between C and G
2 bonds between A and T

Circle the components that make up the nucleotide with cytosine
3 Circles around:
Phosphate group, 2-Deoxyribose, Cytosine

Vegetable Fat Question with CxHy

Initial Rates
3.2 x 10^-4
3.2 x 10^-4
First order
Second order

Bunch of numbers I can remember
1.39
182kg
20000
2.57 x 10^-8 Arrhenius
28.5% percentage yield

Diagram Distillation apparatus
Add condenser and thermometer
Arrows (water in water out). Not sure if that will be a mark

Hydrolysing proteins
6 moldm^-3 HCl

Labelling infrared spectrum
F,G,E

6 marker on the 2 different compounds (one was a cyclic ketone the other was an alcohol)
-boiling points
Hydrogen bonding in one of them stronger than dipole forces
-Cnmr from data sheet
-infrared spec from data sheet

CO2 how does it cause global warming
It is a greenhouse gas and so absorbs infrared from the sun, keeping it in the atmosphere

Minimum number of amino acids in mixture
7

How to see the amino acids
Fluorescent dye and UV/Ninhydrin
(A locating agent was added)

How can they tell if the sample has dried by adding anhydrous salt
Apparently the salt stops clumping together

The weird question on Z,Z adding the carbons to a skeletal formula
Should have gone to the 14th carbon along the chain
At the Alkene, to show z, the carbon chain should have bent around in a U shape instead of a zig-zag

Name mechanism with benzene
Electrophilic substitution

Reaction with bromine finish off the mechanism
- electrophilic addition forming carbo cation then the second bromine ion adds on. Forms dibromoalkane

Distinguishing between primary and tertiary alcohol
Add acidified potassium dichromate
Orange --> Green
No Change

Last question about nucleophile not being able to attack an Alkene.
I think it’s either:
C=O is polar so the nucleophile can attack the partially positive carbon. The alkene doesn’t have a C=O group so not polar so can’t be attacked by nucleophile.
OR
The nucleophile repels the double bond in the alkene

Insufficient NaH4B added. Test for aldehyde
Add tollens/fehlings
Silver mirror/red ppt

Molecular/Emperical formula question
C5H8 you had to times by 5 to get a whole number
Structure was C=C-C=C

Formula of the dicarboxylic acid with an Mr of 118
HOOC- (CH2)2 -COOH

Explain how high resolution electrospray can be used to differentiate between two compounds with an Mr of 118.
High resolution shows the Mr of a molecule to more decimal places

Draw two structures for C6H3Br3
One with One peak in C nmr
One with 4 peaks in C nmr
Benzene ring/kekule structure (several correct answers for this one)

Synthesis question
Nitrobenzene to amine equation finish off equation
Add 6[H] to form 2H2O

Reagents for the reduction of nitrobenzene
Reagents are HCl and Tin catalyst (more than one correct answer for this one)

Reagents and conditions for 2 step synthesis to form an amine
1. KCN aqueous ethanolic/reflux
2. Hydrogen and nickel catalyst/high temp and pressure

The last mechanism (show the first step)
There should have been a H- ion with a lone pair

Dicarboxylic acid titration with NaOH, find the moles in 250cm^3
Can’t remember but had to divide miles by two because it had two COOH and so was a 2:1 reaction

The other product that could have been made in the amine reaction
It could have undergone further substitution to get a tertiary amine (had to draw it)

Explain why amine is a strong base than ammonia
The alkyl group has a positive inductive effect on the nitrogen atom and hence its lone pair of electrons are more available to accept H+ ions

Ffs I drew a single circle around all 3 components for the cytosine question. Would I get one mark?

What question involved the tin catalyst and HCI, I can't even remember that question

Did we have to name a ketone?

i think it was like write the reagants for one of the steps??

Did we have to name a ketone?

I hope so, I don’t remeber it saying components tbh

Mass spec question was just higher precision will distinguish between them because they're the same to the nearest whole number.

D with 4 peaks on 13C spectrum was 1,2,3-tribromobenzene - C2,C3,C4,C5 symmetrical same as C2,C1,C6,C5

Isomer of C4H8Br2 with 2 singlet peaks on 1H spectrum structure was C(CH2Br)(Br)(CH3)2

The question said circleS so I’m assuming it wants more than one circle and it definitely said components. I could be wrong but that’s how I interpreted it

do you have the working out for that
a friend explained howw its 28.4%

yeah we did

Did we have to name a ketone?