The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

WJEC AS-Level Chemistry U2 [New AS] 10/6/16

Scroll to see replies

I worked out the energy per gram but not the CO2. How many marks would I lose?


Posted from TSR Mobile
Would you say around 68/80 for full UMS?
Anyone else get 2-chloro-2 3-dimethylbutanoic acid for the very first question? It tripped me up for some reason... also I didn't get 30% for the percentage yield, I got something like 17.7%. How did you get 30%? I'm intrigued to see what I did wrong.
Original post by owen.williams
Anyone else get 2-chloro-2 3-dimethylbutanoic acid for the very first question? It tripped me up for some reason... also I didn't get 30% for the percentage yield, I got something like 17.7%. How did you get 30%? I'm intrigued to see what I did wrong.


Yeah I had something like that for the first question.
Original post by RasputinReborn
Did you find the number of moles of ethanoic acid (I think) then use molar ratios which was 1:1 then used mass= number of moles X Mr, then divided by the actual mass?


Posted from TSR Mobile


Ah I forgot to multiply by the Mr... That makes sense. I was rushing at that point. And yeah 3-Chloro-2,4-dimethylpentanoic acid is what I put, not what I just said.
Original post by RasputinReborn
Did anyone draw a like a coffee cup calorimeter for the HCl and Mg? I put a cup with a lid and a hole in the lid where the thermometer goes and with some cotton wool around it. Anyone have anything similar?


Posted from TSR Mobile


Yeah, I winged that question and drew a cup with some insulation and a lid with the thermometer through a hole in the top.
Original post by RasputinReborn
Guys, what were the 5 marks for propene?

My guesses

Mention of Pi bond (1)
Sideways overlap of p orbitals(1)
Pi bond has high electron density, allowing it induce other molecules to break the Double bond (1)
Mention of sigma bonds (1)
8 sigma bond in the molecule (1)
120 degree bond angle in unsaturated part of molecule but 109.5 degree in saturated (1)

All I could think of :/




Posted from TSR Mobile


I think you had to relate it to reactivity too if I recall correctly. But yes I used the information we'd been taught on the structure of ethene and applied it to the double carbon bond in propene.
Reply 27
Avatar for Lil670
Lil670
1
For the energy profile with the Ea and enthalpy change labelled in section A, was it a exothermic or endothermic reaction?
Original post by RasputinReborn
I had 3-Chloro-2,4-dimethylpentanoic acid

Edit: I just looked on the Internet and the compound you listed doesn't seem to exist.

Posted from TSR Mobile

I got the same :biggrin:
Original post by Lil670
For the energy profile with the Ea and enthalpy change labelled in section A, was it a exothermic or endothermic reaction?


I had endothermic, as it was the opposite of respiration which was exothermic.
Original post by RasputinReborn
Perhaps one of the more difficult questions on the paper was the reason why Efan got a lower enthalpy change then Sian. Did anyone else say that Mg is now an excess and HCl isn't, therefore HCl is used in the calculation, and then use maths to back it up?


Posted from TSR Mobile


Yes I did exactly this, then I used the ΔT = 14.5°C and worked out Elfed's ΔH as something like -303KJmol-1 and Sian's as -364KJmol-1. I realised after though that we can't actually assume that Elfed's ΔT would be the same as Sian's... so I'm not 100% sure I backed my statement up with the correct maths.
Original post by RasputinReborn
We better get As for getting this bs right. Usually it's "heat lost to surroundings" or something easy like that, haha.


Posted from TSR Mobile


I'm wondering what the grade boundaries are going to be like...I've just been looking and the hardest CH1 since 2011 was the 2014 paper and you needed 71% for an A, and for CH2 it was 2015 and you needed 66% for an A. Both this year's papers have been considerably harder than those past papers so we can cross our fingers and hope they're lower than those.
Original post by RasputinReborn
But when it reacted with H2SO4 it gave C4H8, so how did you get propanol?


Tbh I can't remember. Maybe I did put butanol. My mind tends to blank after exams.
Original post by owen.williams
Yeah, I winged that question and drew a cup with some insulation and a lid with the thermometer through a hole in the top.


Do u have to show the lid or?
Yeah bro, literally everything you've asked, "did anyone put this" yeah we've put the same stuff down. Well done😉 that's exactly what I did and worked it out to -606.somethingkJ per Mole and then also said that the hcl was less concentrated i.e 0.5molar to 0.1molar so reaction is slower and more heat loss resulting in less temp mesured on the thermometer so the %error of that thermometer is greater.
I'm pretty sure I got the percentage error one correct, not sure though. Isn't percentage error
MAX-MIN/2 x100.
So I did 0.2-01/2x100=5% bang on which seems a decent figure? Not sure it's right but like she has potential as they say😏😂😂
Wasn't the 0.2 the mass used in a different experiment though?


Posted from TSR Mobile
Original post by RasputinReborn
Honestly mate, no one knows anymore😂. The maths in chemistry AS this year has been harder than C1 :/


Posted from TSR Mobile


I completely agree 😂 id take another C2 over the maths in chem. Someone put on Twitter how they've lowered to boundaries. I also heard a school gave the paper to a teacher with a PHD in maths and he couldn't do them.


Posted from TSR Mobile
Original post by RasputinReborn
What? No way, PhD in maths? 😂 well tbf, I doubt maths teachers do as much converting between units as us😂


Posted from TSR Mobile


True 😂 but yeah apparently anyway. The chem teachers disagreed with each other on like 15 marks too


Posted from TSR Mobile
Original post by pharmhopeful16
I completely agree 😂 id take another C2 over the maths in chem. Someone put on Twitter how they've lowered to boundaries. I also heard a school gave the paper to a teacher with a PHD in maths and he couldn't do them.


Posted from TSR Mobile


Wouldn't be surprised if overall for Chemistry this year it was A)60% B)50% C)40% etc... usually from what I can tell it's about A)75% B)65% C)60% etc... It's difficult for anyone to be able to predict grade boundaries but the papers this year were considerably more difficult than any past paper I revised from the old spec. I guess it all depends on how people have really done.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you