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AQA Chemistry Paper 2 AS Level 2016 Unofficial Mark Scheme

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ohhh i think it was when you increase the temp Kc and yield both increases?

forward reaction is endothermic and because kc was directly proportional to the products an increase in products means an increase in kc so yes you are correct

Reply 21

haes

Original post by DaVinciGirl

The methanol one was 4 Sig
And the ethanol one was 3sig

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i'm slightly confused here... i forgot which of these were which but the 3 mark question where we had to find an answer in kJ, shouldn't the answer be 11800 and not 11760 because the volume of whatever it was was only 3 sig figs?

Reply 22

Competence

Wasn't uncertainity 2.6% because its +-0.5degrees so u x the 1.3 by 2?

Reply 23

DaVinciGirl

Original post by cordelia_hughes

NO and CO reaction isn't balanced
2NO+2CO-->2CO2 + N2

Sorry about that, had to type it quickly. But yeah you're right thanks!

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Reply 24

Splaffie

Original post by koolgurl14

i got 10.5. most ppl got 10.5

it is 10.5, (4.40/2)/((0.7/2)*(1.2/2)) = 10.5

(edited 7 years ago)

Reply 25

Competence

Original post by haes

I wrote 11800 because it said " to appropriate signifcant figures"

Reply 26

DaVinciGirl

Original post by Splaffie

i believe you can also talk about zeolites for the separation of octane and isooctane, also wasnt the percentage uncertainty (1/38)*100 since it was + or minus 0.5 which means that the value can deviate by 1?

It was the total uncertainty/actual value. I really can't remember if that was 0.5 or 1? All I remember that I did the bigger percentage uncertainty divided by 38. Sorry about that.

Reply 27

AdamWallisjr

Original post by quinn f

do any of you know if it matters which side you put your dot in the Cl free radical?

It does...But I dont remember which side it was....Well my teacher said it does..

Reply 28

Emibear

Original post by Splaffie

forward reaction is endothermic and because kc was directly proportional to the products an increase in products means an increase in kc so yes you are correct

great thought so thank you :biggrin:

Reply 29

quinn f

I saved my answers to the first 10 mcq's on my calculator (had to rush the others), I got (in order): CDDBAADCAB

Reply 30

haes

Also another reason for why the enthalpy calculated is different to the data book could be due to evaporation of water? i think?

Reply 31

cordelia_hughes

Original post by quinn f

I think the CO and NO reaction is CO + NO --> CO2 + 1/2 N2

Yes on all the mark schemes I've seen they accept both 1/2 N2 and the reaction x2

Reply 32

Splaffie

Original post by haes

Also another reason for why the enthalpy calculated is different to the data book could be due to evaporation of water? i think?

that seems fine, q = mcdeltat so q is directly proportional to m, reducing m reduces t, however i still think its because the data book values use average bond enthalpy

Reply 33

DaVinciGirl

Original post by haes

Also another reason for why the enthalpy calculated is different to the data book could be due to evaporation of water? i think?

I put evaporation of the fuel, after the mass was measured, so the mass of fuel was different.

Reply 34

abxo

Original post by zigocarn

How many marks for the mechanism and how many for the explanation in your opinion out of 7?

usually 2

Reply 35

quinn f

Original post by DaVinciGirl

I put evaporation of the fuel, after the mass was measured, so the mass of fuel was different.

I put impure methanol. I'm really not sure about that question

Reply 36

Splaffie

Original post by DaVinciGirl

I put evaporation of the fuel, after the mass was measured, so the mass of fuel was different.

the fuel cant evaporate (outside of the burner anyway), its soaked up by the wick of the spirit burner and is then combusted

(edited 7 years ago)

Reply 37

DaVinciGirl

Original post by zigocarn

How many marks for the mechanism and how many for the explanation in your opinion out of 7?

I think by looking at previous past papers, one mark for naming, 4 marks for mechanism, and 2 marks for explaining.

Reply 38

DaVinciGirl

Original post by Splaffie

the fuel cant evaporate, its soaked up by the wick of the spirit burner and is then combusted

It states in Chemrevise that error in method can be evaporation of fuel after weighing

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Reply 39

GabbytheGreek_48

Original post by DaVinciGirl

Still In Process and editing

1.1 Kc=[product]/[Reactant 1][Reactant 2]
Unit- mol^-1dm^3

1.2 10.5 mol^-1dm^3

-Equation for Cl free radical and ozone layer
Cl.+ O3 ---> ClO.+ O2
ClO.+ O3 ----> 2O2 + Cl.
-Drawing chloropentafluroethane
Screen Shot 2016-06-10 at 16.23.33.png

-Why those the molecule (one without Cl) not contribute to ozone depletion? Because doesn't have a C--Cl bond so no chlorine free radical is made.

-Number of molecules + Avogadro constant question? 1.01 x 10^25

-Isooctane? Nomenclature- 2,2,4-trimethypentane
-Name how to separate Isooctane and octane and how?
Distillation and you heat the conical flask with temperature above 99 degrees so Isooctane compound vaporises but the other compound remains liquid. Condense in a cooling jacket.

-Oleic acid testing for unsaturated
Bromine water and Observation from orange to colourless

-Enthalpy change of Combustion of methanol- -307 kJmol^-1
-Why enthalpy change lower- neglecting the specific heat capacity of the calorimeter
-Uncertainty- 0.5/38*100= 1.31%
-Why Uncertainty of 0.5 is okay?
-Heat change for ethanol 11760 KJ maybe 11800KJ as it's in 3sf (I have a blurry memory about this one)

-Catalyst how it works
Lowers activation energy by providing an alternate route to a reaction
-How does NO and CO react?
2NO + CO ----> N2 + CO2
-Thin layer catalyst maybe because it's more cost effective and catalyst doesn't get used up during reaction so you don't need thick layer.

-Infrared Radiation: O-H bond and 3230-3550 cm^-1

6 Marker: Alcohol (hydrogen bonds, permanent dipole dipole, van der waals) Aldehyde (permanent dipole dipole and van der waals) and alkane (van der waals)

7 Marker electrophilic addition
Outline Mechanism: arrow from double bon to H(delta plus) arrow from bond H---Br to Br)
Tertiary Carbonation ion is more stable than secondary carbocation because alkyl groups is electron releasing and stabilises the carbocation. So most stable carbocation is formed more. 3bromo is more stable than 2bromo.

-Excess find moles of both and magnesium has more less moles than the other compound so more magnesium is needed for a the first compound to work

-Acidified potassium dichromate display formula both ketone and carboxylic acid and equation
Screen Shot 2016-06-10 at 16.48.19.png

CH3CH(OH)CH2OH + 3[O] → CH3COCOOH + 2H2O

-Reflux Apparatus
Screen Shot 2016-06-10 at 16.44.46.png

-AntiBumping Granules

-What is the structure when not in excess?
Aldehyde and ketone one

Multiple Choices
-orange to red, aldehyde one with cho-
-Increase Temp- makes KC increase and yield increase C
-Last question multiple choice is C
-The C,H,O is B- ethanoic acid
-Nucleophilic Substitution
-Total Equilibrium moles 18
-The Cyclohexene general formula- CnH2n-2
-Cracking equation A
For the first 10 questions these may be the answers credit to @quiin f : CDDBAADCAB