AQA A Level Chemistry Paper 3 20th June 2018 Unofficial Markscheme

So temp change was?..

What was the actual temp for the 4th minute

-33.6 kjmol-1
0.0012?moldm-3s-1
0.0004 ish as rate
76%
9.5% uncertainty, decrease uncertainty but increasing concs of acid and alkali so greater temp change
Lower pressure + higher temp
Entropy change large and positive
Largest mass of ppt was the one where both baso4 and mg(oh)2 formed
Na + O₂ = yellow flame and white smoke. P4 + O₂ white smoke
Aluminium highest melting point
Bromophenl blue indicator
Decolorises bromone water
Sodium carbonate removes H+ left from phosphoric acid
Open tap to prevent build up of CO₂
On one multiple choice question it was choosing which reaction can occur and I put the elimination one with the KOH
Lithium iodide has most covalent character
Rate equation [X][Y]

Does anyone remember anymore multiple choice questions?

25cm3 and 75cm3 so a total of 100cm3. density is 1 so mass is 100gram
using Q=mcdelta t .... 100 x 3.2 x 4.2 = 1344 joules = -1.344 kilojoules (negative as its exothermic) ...

0.02 mols of acid and 0.045 mols of KOH so using balance symbol equation 0.04 mols of KOH reacted with 0.02 mols of acid (0.005 mols of KOH in excess. mole ratio of KOH:h20 was 2:2 or ratio of acid:h20 is 1:2 so 0.04 moles of h2o

divide -1.344 by 0.04 to get -336kjmol-1 hope that helps and makes sense

what rate did you get when [H+] is 0.35? did you just have to find the gradient of the tangent at 0.35 because in the question it said only concentration of I- affected rate?

So temp change was?..

i got 2.1

-33.6 kjmol-1
0.0012?moldm-3s-1
0.0004 ish as rate
76%
9.5% uncertainty, decrease uncertainty but increasing concs of acid and alkali so greater temp change
Lower pressure + higher temp
Entropy change large and positive
Largest mass of ppt was the one where both baso4 and mg(oh)2 formed
Na + O₂ = yellow flame and white smoke. P4 + O₂ white smoke
Aluminium highest melting point
Bromophenl blue indicator
Decolorises bromone water
Sodium carbonate removes H+ left from phosphoric acid
Open tap to prevent build up of CO₂
On one multiple choice question it was choosing which reaction can occur and I put the elimination one with the KOH
Lithium iodide has most covalent character
Rate equation [X][Y]

Does anyone remember anymore multiple choice questions?

25cm3 and 75cm3 so a total of 100cm3. Density is 1 so mass is 100gram
using q=mcdelta t .... 100 x 3.2 x 4.2 = 1344 joules = -1.344 kilojoules (negative as its exothermic) ...

0.02 mols of acid and 0.045 mols of koh so using balance symbol equation 0.04 mols of koh reacted with 0.02 mols of acid (0.005 mols of koh in excess. Mole ratio of koh:h20 was 2:2 or ratio of acid:h20 is 1:2 so 0.04 moles of h2o

divide -1.344 by 0.04 to get -336kjmol-1 hope that helps and makes sense

y 2drquadrule

i put rate [w]2[y] because if you double it rate will quadruple. conc of catalyst doesnt affect rate. would doubling x just increase rate by 2 as its first order?

6 marker:
- keep other reactants conc constant
- total volume must be same in all experiments
- place X in conical flask in water bath, with a white tile (with an X drawn on it)
- add product of reaction and time how long it takes for the cross to appear (as dark blue colour dissapears)
- record time and conc
- repeat for different conc of A
- plot conc v time graph
- tangent at t=0
- initial rate is gradient of tangent drawn

Anyone correct me if im wrong? Also got 2.1 for temperature change.

agree with you for most of them!
I put CsI for the most covalent character, lithium is smaller than cs so it would have a higher charge density, polarise the bond more?
3 peaks in the NMR spectrum of 1,4-dinitrobenzene
4 isomeric aldehydes with 5 carbon atoms
i put the organic compound would react with KCN in a nucleophilic substitution reaction, because there were 2 double bonds next to the C-Br I couldn't see how another double bond could form
Cr for the electrochem one (wasn't sure)
atomisation of iodine: half a mole of Iodine (s) --> one mole of I atoms (g)

not multiple choice, but the drying agent was suitable because it was insoluble in cyclohexene/doesn't react with cyclohexene
improve the calorimetry experiment by putting a lid on the beaker

For calculating the enthalpy change, did the question give us delta T? I can’t remember. Or did people use delta calculated from the graph?

HNO3 + H2SO4 -----> [H2NO3]+ + [HSO4]-
and then
[H2NO3]+ -----> [NO2]+ + H2O


clearly in the first step of the equation HNO3 is accepting the proton from the H2SO4 so it's acting as a base.



Just some random answers:


Why is Sodium HydrogenCarbonate used etc...?

Reacts with any excess acid that may be present on the cyclohexene produced.

Why is the Lid periodically released every time?

Allows the CO2 produced to escape to prevent the build up of pressure that may cause explosion.

How would you decrease the percentage uncertainty using the same thermometer?

To decrease the percentage uncertainty, the Temperature change should be larger therefore using a larger concentration of reagents would cause a larger temperature change?

Why is the H2O2 and I-? else used in excess?

Using the reagents in the initial step in Excess would mean that the concentrations can be assumed to be constant over time. As the concentration remains constant this means the order of reaction for these reagents shall be zero as they shall have no effect on the rate of reaction due to them not changing.

How can we limit the heat loss to the surrounding?

A lid/ insulate the calorimeter

Why does Sulphuric acid have a more negative enthalpy change than ethanedioic acid?

I wasn't too sure on this, but I mentioned that Sulphuric acid fully dissociates it's hydrogen ions whereas ethanedioic acid only partially dissociates it's ions (Sulphuric acid is a stronger acid than ethanedioic acid) this means the energy released when The Hydrogen ions from sulphuric acid forms bonds shall be greater?
I may be wrong, I wasn't too sure.


Some random multiple choice answers:

Ethylamine > Ammonia > Phenylamine

The helium ion passed through the nucleus which shows it's mostly empty space.

The helium ions were partially reflected which shows there's a small positive nucleus.

Cr3+ was the thing that couldn't react with h2o2 and something else I think,because it has the most negative Eo value.

The alcohols can be made by a Alkaline hydrolysis of an ester I think?

HNO3 is behaving as a base.

LiF as the biggest difference between Born haber and data book (Reasoning for this was because both the ions will be sooo small that they can get so close so there will be quite a lot of electron overlapping so a lot of covalent character)

If you remind me of any multiple choice questions, I'll be able to provide some answers.

agree with you for most of them!
I put CsI for the most covalent character, lithium is smaller than cs so it would have a higher charge density, polarise the bond more?
3 peaks in the NMR spectrum of 1,4-dinitrobenzene
4 isomeric aldehydes with 5 carbon atoms
i put the organic compound would react with KCN in a nucleophilic substitution reaction, because there were 2 double bonds next to the C-Br I couldn't see how another double bond could form
Cr for the electrochem one (wasn't sure)
atomisation of iodine: half a mole of Iodine (s) --> one mole of I atoms (g)

not multiple choice, but the drying agent was suitable because it was insoluble in cyclohexene/doesn't react with cyclohexene
improve the calorimetry experiment by putting a lid on the beaker