AQA A level chemistry 2020 autumn paper 2 unofficial MS

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Poll: your estimated marks for this paper?
>=95 (25)
17.01%
85-94 (15)
10.2%
70-84 (28)
19.05%
65-69 (20)
13.61%
60-64 (21)
14.29%
50-59 (16)
10.88%
40-49 (7)
4.76%
30-39 (4)
2.72%
20-29 (3)
2.04%
<=19 (8)
5.44%
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ish101
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in progress, i've started it off, just add answers and Q numbers below and i'll add it on

1.1 rates/tangent, 8cm^3s^-1 [3]
1.2 order of reaction, order 2 and inversely proportional [2]
1.3 ?
1.4 diagram, just a labelled gas syringe with no gaps anywhere to prevent leaks [1]
1.5 effect of halving concs, 1/8 [1]
1.6

k2cr07 as an oxidising agent Q
2.1 Q,R,S,T and goes from orange to green [2]
2.2 T (the aldehyde), silver mirror formed [2]
2.3 explain fully how IR spectroscopy can be used to distinguish between P,Q and T (which 3 was it)? only one of them show peak at 1680-1750 due to C=O, others both show an OH alcohols peak at (...). you can use the unique fingerprint regions of the 2 to further distinguish them [4]
2.4 ?
...

amino acid hydrolysis
x.1 ? []
x.2 tick the boxes for each functional group present, it was amide and amine only [1]
x.3 phenylamine and a sort of long chain carboxylic acid with a nitrogen attached in between [2]
x.4 enzyme has a specific tertiary structure which means that its active site is stereospecific, so only 1 enantiomer can bind to it [2]

synthesis Q
x.1 synthesis route, conditions. REACTION TYPE friedel crafts acylation (not electrophilic substitution), with ethanoyl chloride and AlCl3, under reflux [3]
x.2 2nd synthesis, conditions. MECHANISM nucleophilic addition, with aqueous NaBH4 and dilute acid, [3]
x.3 aspirin production equation, draw in ethanoic anyhdride on left and ethanoic acid on right [1]
x.4 ethanoic anhydride in XS, 6.6g (7.9g if you ignored the % yield) [5]
x.5 why is mass spec not suitable for this? they don't have the same Mr [1]

practical
x.1 fill in step 4: reweigh the boat after addition/add in washings of boat to flask, so that none of the acid is left over [2]
x.2 ?
x.3 ?
x.4 ?

nmr
7.1
6 marker, TMS is the standard that all others are conventionally measured against, given a wavenumber of 0. has 12 hydrogens all in same environment, so one easily distinguishable peak is produced on every spectrum. it's also inert, so wont interfere with other substances its with. the other 2 are solvents, with no hydrogens at all (D is deuterium which is a hydrogen isotope) so no peak produced due to them, won't confuse any readings. they are inert so wont interfere with substances.i drew the displayed formulae for each to emphasise the points, didn't know what else to say [6]
7.2 doublet quartet doublet [3]
7.3 ? [1]
7.4 isomers, 5-chloro-2,2-dimethylbutan-3-one and 2,2-dimethylbutanoyl chloride in some order [2]
7.5 complete the beginning of the formula, 2-hydroxy ... [1]

kc
9.1 find no. of moles of B and C, [B]=0.24, [c]=0.32? [2?]
9.2 kc calc? straightforward, just sub given numbers into given equation [2]
9.3 why is water not in the kc expression, because the reagent and reactant are in aqueous solution so addition of water will affect the concs of the other 2 anyways [1]
9.4 find conc of product (whatever it was) at equilibrium given that kc=37. 44moldm^-3 (it doesn't seem right to me, but most ppl got this) [4 or 5? i think 4]
9.5 mechanism with water? dehydration of ethanal i think [3]
9.6 chlorine is more electronegative than carbon, so it pulls e-s towards itself, decreasing the + charge on the delta+ C and making it less susceptible to attack by nucleophiles (H2O in this case) [3]
Last edited by ish101; 9 months ago
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random678
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thanks so much for this!!
1.1 - i got 1.5 but probs im wrong
7.4 - swear there was a mistake in this question? they had drawn out the skeletal formula with 5 carbons but had written ' pent ' idk i could be wrong
x.5 i got the relative molecular masses are the same
8.1 - i gto for B 0.32 something and similair value for C because yoou had to multiply moles at equilibrium by 2 and minus to get B but not multiply by 2 for C
8.4 was just the mechanism drawing out arrows
8.5 i just spoke about bond enthallpy and theres no acid cataylst speeding up rate of reaction ngl waffled alot
2.3 wrote about c double bond o for one isomer but i just couldnt get it for r and s

cant remember the rest ngl im so annoyed because i knew it was doublet but my dumbass thought no thats not even a thing and i wrote singlet so only got 1/3 for that q ughhhh
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Anonymous17!
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I got 5.55x10^-3 s^-1 for 1.1 And this question- synthesis route, conditions. electrophilic substitution, with ethanoyl chloride and AlCl3, under reflux They asked for the type of REACTION for the first part and the MECHANISM for the second part.For step 1, the REACTION type is FRIEDAL CRAFTS ACYLATION, the MECHANISM is ELECTROPHILIC SUBSTITUTION For step 2, they asked for the MECHANISM, in which nucleophilic addition with NaBH4 is correct. But I imagine they caught most people out with step 1.
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ish101
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(Original post by random678)
thanks so much for this!!
1.1 - i got 1.5 but probs im wrong
7.4 - swear there was a mistake in this question? they had drawn out the skeletal formula with 5 carbons but had written ' pent ' idk i could be wrong
x.5 i got the relative molecular masses are the same
8.1 - i gto for B 0.32 something and similair value for C because yoou had to multiply moles at equilibrium by 2 and minus to get B but not multiply by 2 for C
8.4 was just the mechanism drawing out arrows
8.5 i just spoke about bond enthallpy and theres no acid cataylst speeding up rate of reaction ngl waffled alot
2.3 wrote about c double bond o for one isomer but i just couldnt get it for r and s

cant remember the rest ngl im so annoyed because i knew it was doublet but my dumbass thought no thats not even a thing and i wrote singlet so only got 1/3 for that q ughhhh
np just added some stuff, remembered some of the values too, ty for the help
dw it's not a massive issue it was only a couple marks
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purplewriter
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I don't remember which question it was, I think it was somewhere near the start, about how an enzyme can catalyse hydrolysis of one compound, but not the other. And I put because it's complementary to the active site so fits into it and stuff
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Anonymous17!
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(Original post by ish101)
in progress, i've started it off, just add answers and Q numbers below and i'll add it on

1.1 rates/tangent, 8cm^3s^-1 [3]
1.2 order of reaction, order 2 and inversely proportional [2]
1.3 ?
1.4 diagram, just a labelled gas syringe with no gaps anywhere to prevent leaks [1]
1.5 effect of halving concs, 1/8 [1]
1.6

k2cr07 as an oxidising agent Q
2.1 Q,R,S,T and goes from orange to green [2]
2.2 T (the aldehyde), silver mirror formed [2]
2.3 explain fully how IR spectroscopy can be used to distinguish between P,Q and T (which 3 was it)? only one of them show peak at 1680-1750 due to C=O, others both show an OH alcohols peak at (...). you can use the unique fingerprint regions of the 2 to further distinguish them [4]
2.4 ?
...

aspirin
x.1 synthesis route, conditions. electrophilic substitution, with ethanoyl chloride and AlCl3, under reflux [3]
x.2 2nd synthesis, conditions. nucleophilic addition, with aqueous NaBH4 and dilute acid, [3]
x.3 aspirin production equation, draw in ethanoic anyhdride on left and ethanoic acid on right [1]
x.4 ethanoic anhydride in XS, 6.6g (7.9g if you ignored the % yield) [5]
x.5 why is mass spec not suitable for this? they don't have the same Mr [1]

nmr
7.1
6 marker, TMS is the standard that all others are conventionally measured against, given a wavenumber of 0. has 12 hydrogens all in same environment, so one easily distinguishable peak is produced on every spectrum. it's also inert, so wont interfere with other substances its with. the other 2 are solvents, with no hydrogens at all (D is deuterium which is a hydrogen isotope) so no peak produced due to them, won't confuse any readings. they are inert so wont interfere with substances.i drew the displayed formulae for each to emphasise the points, didn't know what else to say [6]
7.2 doublet quartet doublet [3]
7.3 ? [1]
7.4 isomers, 5-chloro-2,2-dimethylbutan-3-one and 2,2-dimethylbutanoyl chloride in some order [2]
7.5 complete the beginning of the formula, 2-hydroxy ... [1]

kc
8.1 find no. of moles of B and C, [B]=0.24, [c]=0.32? [2?]
8.2 kc calc? [2]
8.3 why is water not in the kc expression, because the reagent and reactant are in aqueous solution so addition of water will affect the concs of the other 2 anyways [1]
8.4 mechanism with water? dehydration of ethanal i think [3]
8.5 chlorine is more electronegative than carbon, so it pulls e-s towards itself, decreasing the + charge on the delta+ C and making it less susceptible to attack by nucleophiles (H2O in this case) [3]
X.1 they asked for the reaction type, not the mechanism. So it isn’t electrophilic subsition, it’s friedal crafts Acylation.

Thank you for starting this mark scheme. How did you calculate the rate for 1.1?? I drew a tangent at the point (0,0) and then did change in vertical over change in horizontal. I also converted the vertical into dm^-3 as it was cm^-3 but conc is measured in mol dm^-3. So I think a conversion was necessary, either from cm to dm or from dm to cm. I can’t remember the exact values I got but I ended up with 5.55x10^-3.
Last edited by Anonymous17!; 9 months ago
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Harrybeld
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(Original post by Anonymous17!)
I got 5.55x10^-3 s^-1 for 1.1 And this question- synthesis route, conditions. electrophilic substitution, with ethanoyl chloride and AlCl3, under reflux They asked for the type of REACTION for the first part and the MECHANISM for the second part.For step 1, the REACTION type is FRIEDAL CRAFTS ACYLATION, the MECHANISM is ELECTROPHILIC SUBSTITUTION For step 2, they asked for the MECHANISM, in which nucleophilic addition with NaBH4 is correct. But I imagine they caught most people out with step 1.
That's so sneaky lol the more I read these forums, the more stupid marks I know I've lost lol.
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random678
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(Original post by Harrybeld)
That's so sneaky lol the more I read these forums, the more stupid marks I know I've lost lol.
literally me rn lmao
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random678
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also i wrote acylation not friedel crafts would i stilll get the mark? and for the enzyme question i wrote about stereospecific active site being complimentray my brain started going in biology mode so idk if they'll give me full 2 marks and for the rate one i drew a tangent got 2 coordinates and did change in y over change in x
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Harrybeld
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(Original post by random678)
literally me rn lmao
And that's before marks I've lost on just genuinely getting the questions wrong aha. I need an A and I feel like that's just not going to happen. What grade are you aiming for?
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ish101
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(Original post by Anonymous17!)
X.1 they asked for the reaction type, not the mechanism. So it isn’t electrophilic subsition, it’s friedal crafts Acylation.

Thank you for starting this mark scheme. How did you calculate the rate for 1.1?? I drew a tangent at the point (0,0) and then did change in vertical over change in horizontal. I also converted the vertical into dm^-3 as it was cm^-3 but conc is measured in mol dm^-3. So I think a conversion was necessary, either from cm to dm or from dm to cm. I can’t remember the exact values I got but I ended up with 5.55x10^-3.
i see what you did, mine is just a measure of the average gas volume given off per second which technically should be correct, + you had to give units so i think our methods should be equally valued, given the right numbers
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random678
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(Original post by Harrybeld)
And that's before marks I've lost on just genuinely getting the questions wrong aha. I need an A and I feel like that's just not going to happen. What grade are you aiming for?
honestlyyy im such a dumbass i thought 'doublet' wasnt a thing bc it sounded dumb so i wrote singlet turns out it was doublet -_-
andd im hoping to get a B at least but paper 1 and 2 have gone so bad so idek at this point, are you reapplying for 2021??
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ish101
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(Original post by Anonymous17!)
I got 5.55x10^-3 s^-1 for 1.1 And this question- synthesis route, conditions. electrophilic substitution, with ethanoyl chloride and AlCl3, under reflux They asked for the type of REACTION for the first part and the MECHANISM for the second part.For step 1, the REACTION type is FRIEDAL CRAFTS ACYLATION, the MECHANISM is ELECTROPHILIC SUBSTITUTION For step 2, they asked for the MECHANISM, in which nucleophilic addition with NaBH4 is correct. But I imagine they caught most people out with step 1.
are you 100% sure? so was it: 1. type, reagents, conditions and 2. mechanism, reagents, conditions
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Anonymous17!
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(Original post by random678)
also i wrote acylation not friedel crafts would i stilll get the mark? and for the enzyme question i wrote about stereospecific active site being complimentray my brain started going in biology mode so idk if they'll give me full 2 marks and for the rate one i drew a tangent got 2 coordinates and did change in y over change in x
No. Because Acylation is for aliphatic pathways, this wa son benzene so it needed to be the aromatic reactions which is friedal crafts Acylation. Sorry
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random678
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i didnt write nabh4 i wrote h3po4 omg ive lost another mark:mad:
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Harrybeld
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(Original post by random678)
honestlyyy im such a dumbass i thought 'doublet' wasnt a thing bc it sounded dumb so i wrote singlet turns out it was doublet -_-
andd im hoping to get a B at least but paper 1 and 2 have gone so bad so idek at this point, are you reapplying for 2021??
I've got my offer held for my course so thankfully if I get an A I can just go to there but if not then I've reapplied in the hope of getting some lower offers. What are your plans for next year?
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dontworrymyg
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(Original post by ish101)
are you 100% sure? so was it: 1. type, reagents, conditions and 2. mechanism, reagents, conditions
Yeah I'm doubting it too, I think your right
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Anonymous17!
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(Original post by ish101)
are you 100% sure? so was it: 1. type, reagents, conditions and 2. mechanism, reagents, conditions
Yes. It was
Reaction type,
Reagents
Contains

And then
Mechanisms
Reagents
Conditions

That’s how they caught you out. They asked for the reaction type. It was sneaky. But I’m 100% sure.

For anyone who is doubting it, and in case it isn’t correct and I’m remembering it wrong, I’ll ask my teacher tomorrow and update this post. He gets access to the question paper the day after the exam so if he gets it, I’ll ask him to double check but I do distinctly remember it being type of reaction.
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ish101
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(Original post by Anonymous17!)
Yes. It was
Reaction type,
Reagents
Contains

And then
Mechanisms
Reagents
Conditions

That’s how they caught you out. They asked for the reaction type. It was sneaky. But I’m 100% sure.

For anyone who is doubting it, and in case it isn’t correct and I’m remembering it wrong, I’ll ask my teacher tomorrow and update this post. He gets access to the question paper the day after the exam so if he gets it, I’ll ask him to double check but I do distinctly remember it being type of reaction.
right, i've added a bit above to make that clear, i do remember friedel crafts acylation popping into my head first, then me changing it to el. sub. so i think you're probs right. "reaction type" is quite vague and misleading imo, don't like that v much
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dontworrymyg
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Isn't 9.3 because water was in excess so the concentration of water is effectively constant?
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