2017 AQA AS Chemistry paper 2 discussion/unofficial markscheme

Watch
Lilith2400
Badges: 14
Rep:
?
#1
Report Thread starter 3 years ago
#1
1.) Energy
Curve shifted to the right which has a lower peak and only crosses the original curve once and starts at the origin
Increase in successful collisions due to increased kinetic energy

N=pV/RT
p = 102000 V= 7.2 × 10^-5
Calculate moles and use Mr = mass/moles
Mr for PV=nRT Q was around 80 ??

Empirical formula : C3H7
Molecular formula : C6H14

C3H8 + 5O2 ----> 3CO2 + 4H2O
number of carbon atoms = 13
KJ = -33,100
Plot points and draw a line of best fit which does not extrapolate , draw line from 3 down to the line of best fit and then from this point to the y axis and read off value which was around -55.7 ???

6 marker on compounds :
C - cyclopentane as it didn't decolourise bromine water so only single bonds are present and it has the general formula for an alkene
B- pent-2-ene as it can form E-Z isomers depending on position of groups either side of double bond
A- methylbutane (cant remember numbers) resulted in two groups on one side of double bond being identical so stereoisomers didn't exist Or pent-1-ene for the same reasoning

Percentage yield = around 65 %

Concordant titres are within 0.1 cm^3 of eachother
For titration calc you had to calculate moles and obtain moles of other compound by using the ratio and then use moles = mass /Mr

Nucleophilic substitution , arrow from hydroxide ion to C bonded to Br and then an arrow from bond between C&Br to Br to form alcohol and bromide ion

Other mechanism : elimination
Other organic product : double bond at carbon 1 , cant remember name

Poly(chloroethane) has larger boiling point as it has greater van der waals due to more electrons

Plasticisers are present in PVC as it needs to be flexible to mould around wires , PVC is a strong &hard material

Skeletal formula had 38 hydrogen atoms ??

In dehydration question draw arrow from lone pair on O to H+ , missing structure was the same with positive H -O -H attached , arrow showing H2O coming off and arrow from bond between C and H to the C-C bond to form the double bond
Other alkene structures were similar but the double bond was in different places
It is rearranged as tertiary carbocation is formed which is more stable than secondary carbocations

For second 6 marker : cyclohexene can be removed by fractional distillation as it will have a much lower boiling point as it only van der waals forces between molecules. Reactants mixture both had hydrogen bonds (not sure if this is right i guessed )
2
reply
JustAnotherDude
Badges: 4
Rep:
?
#2
Report 3 years ago
#2
Can confirm that all answers above are correct. Percentage yield is around 65%
N = 13 carbon atoms
-33100 for enthalpy

Amazing paper. Had a blast. Grade boundaries will go up by atleast 2-3 if not more. They were low last year since it was a new specification.
0
reply
chelseafc141
Badges: 12
Rep:
?
#3
Report 3 years ago
#3
I got c6h14 for both ef and mf
0
reply
J__
Badges: 7
Rep:
?
#4
Report 3 years ago
#4
For the 6 marker on compounds, shouldn't A be pent-1-ene, as it does not show E/Z isomers but is still an alkene?
0
reply
J__
Badges: 7
Rep:
?
#5
Report 3 years ago
#5
(Original post by chelseafc141)
I got c6h14 for both ef and mf
Empirical is the simplest ratio
0
reply
Lilith2400
Badges: 14
Rep:
?
#6
Report Thread starter 3 years ago
#6
(Original post by J__)
For the 6 marker on compounds, shouldn't A be pent-1-ene, as it does not show E/Z isomers but is still an alkene?
Yeah i think you could have that too !

Posted from TSR Mobile
0
reply
Saffron76
Badges: 3
Rep:
?
#7
Report 3 years ago
#7
Why was there so much maths again ffs😫
1
reply
Poppylorg
Badges: 2
Rep:
?
#8
Report 3 years ago
#8
(Original post by J__)
For the 6 marker on compounds, shouldn't A be pent-1-ene, as it does not show E/Z isomers but is still an alkene?
Yes, A i got as pent-1-ene B is pent-2-ene and C as cyclopentane. Restricted rotation around c=c bond
1
reply
Poppylorg
Badges: 2
Rep:
?
#9
Report 3 years ago
#9
Calculations for my Mr at the beginning i got 80 point something. And for the mass i got 500 and something. The one where it asked for mg.
0
reply
chelseafc141
Badges: 12
Rep:
?
#10
Report 3 years ago
#10
Was one of the answers heat loss
0
reply
Poppylorg
Badges: 2
Rep:
?
#11
Report 3 years ago
#11
(Original post by ErinMei)
1.) Energy
Curve shifted to the right which has a lower peak and only crosses the original curve once and starts at the origin
Increase in successful collisions due to increased kinetic energy

N=pV/RT
p = 102000 V= 7.2 × 10^-5
Calculate moles and use Mr = mass/moles
Mr for PV=nRT Q was around 80 ??

Empirical formula : C3H7
Molecular formula : C6H14

C3H8 + 5O2 ----> 3CO2 + 4H2O
number of carbon atoms = 13
KJ = -33,100
Plot points and draw a line of best fit which does not extrapolate , draw line from 3 down to the line of best fit and then from this point to the y axis and read off value which was around -55.7 ???

6 marker on compounds :
C - cyclopentane as it didn't decolourise bromine water so only single bonds are present and it has the general formula for an alkene
B- pent-2-ene as it can form E-Z isomers depending on position of groups either side of double bond
A- methylbutane (cant remember numbers) resulted in two groups on one side of double bond being identical so stereoisomers didn't exist Or pent-1-ene for the same reasoning

Percentage yield = around 65 %

Concordant titres are within 0.1 cm^3 of eachother
For titration calc you had to calculate moles and obtain moles of other compound by using the ratio and then use moles = mass /Mr

Nucleophilic substitution , arrow from hydroxide ion to C bonded to Br and then an arrow from bond between C&Br to Br to form alcohol and bromide ion

Other mechanism : elimination
Other organic product : double bond at carbon 1 , cant remember name

Poly(chloroethane) has larger boiling point as it has greater van der waals due to more electrons

Plasticisers are present in PVC as it needs to be flexible to mould around wires , PVC is a strong &hard material

Skeletal formula had 38 hydrogen atoms ??

In dehydration question draw arrow from lone pair on O to H+ , missing structure was the same with positive H -O -H attached , arrow showing H2O coming off and arrow from bond between C and H to the C-C bond to form the double bond
Other alkene structures were similar but the double bond was in different places
It is rearranged as tertiary carbocation is formed which is more stable than secondary carbocations

For second 6 marker : cyclohexene can be removed by fractional distillation as it will have a much lower boiling point as it only van der waals forces between molecules. Reactants mixture both had hydrogen bonds (not sure if this is right i guessed )
I got stuck on pvc question. I thought plasticiser molecules lie between the polymer chain causing the vdw forces to decrease??? Making pvc more flexible due to the vdw forces. I got all the same answers also what did u write about the factors affecting boilingpoint of cyclohexene,cyclohexanol and phosphoric acid.
0
reply
Poppylorg
Badges: 2
Rep:
?
#12
Report 3 years ago
#12
(Original post by chelseafc141)
Was one of the answers heat loss
I wrote the liquid evaporated, reducing your chemicals that you have therefore you get a lower enthalpy. I wouldve said heat loss but it said liquid in the question (hint for evap)
0
reply
Sxmir._
Badges: 7
Rep:
?
#13
Report 3 years ago
#13
I got around 565 mg for the titration 4 marker

Got 33 100 for something

Got around 81.9 for the first calculation
1
reply
Poppylorg
Badges: 2
Rep:
?
#14
Report 3 years ago
#14
(Original post by Sxmir._)
I got around 565 mg for the titration 4 marker

Got 33 100 for something

Got around 81.9 for the first calculation
Do you remember the context for the 33 100 answer? I dont remember any enthalpy questions. Got the same answers as your other calcs
0
reply
Dying Lama
Badges: 3
Rep:
?
#15
Report 3 years ago
#15
I got slapped up by that exam..... The cycle mechanism question and the phosphoric acid destroyed me..... That being said I'm pretty sure I only dropped 2 of the multiple choice qs
0
reply
Poppylorg
Badges: 2
Rep:
?
#16
Report 3 years ago
#16
(Original post by Dying Lama)
I got slapped up by that exam..... The cycle mechanism question and the phosphoric acid destroyed me..... That being said I'm pretty sure I only dropped 2 of the multiple choice qs
Multiple choice was hard af, i accidently ticked boxes instead of filling the circles. Do i lose all my multiple choice marks ?
0
reply
Harj2807
Badges: 7
Rep:
?
#17
Report 3 years ago
#17
I'm afraid you would, aqa are really harsh like that.
0
reply
brrrigid
Badges: 10
Rep:
?
#18
Report 3 years ago
#18
Was anyone else really pressed for time during that exam? Nearly everyone in my group was.
2
reply
afifa p
Badges: 0
Rep:
?
#19
Report 3 years ago
#19
(Original post by Poppylorg)
Multiple choice was hard af, i accidently ticked boxes instead of filling the circles. Do i lose all my multiple choice marks ?
oops u will lose marks because AQA are strict at that unfortunately...
0
reply
IDONTW1N
Badges: 2
Rep:
?
#20
Report 3 years ago
#20
All correct except the poly(chloroethane) answer; it would have a permanent dipole between Cl and C and so greater inter molecular between the polymer layers.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (506)
33.67%
Yes, I like the idea of applying to uni after I received my grades (PQA) (622)
41.38%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (306)
20.36%
I think there is a better option than the ones suggested (let us know in the thread!) (69)
4.59%

Watched Threads

View All