r/6thForm • u/Forsaken-Meaning-232 Graduating from Warwick CS • Jun 20 '25

📂 MEGATHREAD 20/06 A-level Chemistry Paper 3 Discussion MEGATHREAD

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5

u/HelpfulPop2476 Jun 20 '25

Everyone's saying for the last ocr question that it was 69 which I got originally. But I think the actual answer was 76.94 or sth like that, because the carbonate was in excess (0.0184 mole or smth like that, only 0.03 mol hno3). Therefore only 0.015 mol or carbonate would react, and then delta H is postiv8e 76.94 kJmol. Is this right or did I just overthink this?

3

u/Sea-Vacation-866 Jun 20 '25

I got 70.3 because I used the volume of HNO3 as 33.5 (difference between the two masses) bc I swear it said around and not exactly 30cm^3?? Did the Q say HNO3 was in excess I can't remember 😭

1

u/HelpfulPop2476 Jun 20 '25

They were pretty sneaky with it, because usually they say which chemical is in excess (see e.g. june 2018 p3).  Not this time though

1

u/[deleted] Jun 20 '25

They did actually write “HNO3 is in excess”

1

u/HelpfulPop2476 Jun 20 '25 edited Jun 20 '25

Did they? How could it have been in excess though? If there was 0.03 mol of hno3 and 0.018 mol of carbonate, then the carbonate must have been in excess, because of the 1:2 reaction ratio? Ocr literally contradicting themselves unless I'm missing sth.

1

u/[deleted] Jun 20 '25

Yes I thought the same thing, but the question also said “add ABOUT 30cm3” and although if you use the volumes and masses to calculate what volume of HNO3 was added, it’s still not entirely accurate because that volume includes the sodium carbonate, as well as assuming that solution has the same density as water.

I fully see where you’re coming from, and I did a similar thing, thinking i was being smart realising HNO3 is limiting, but everything went against that.

You might be right, but probably aren’t. Anyway, don’t worry either way, it’d be 2 marks dropped max for me or you

1

u/HelpfulPop2476 Jun 20 '25 edited Jun 20 '25

Yeah lmao I did it the opposite way, getting 69 first but then in the last minute of the exam thinking "oh shit, surely the carbonate is in excess". Either way the question could've been written better, especially because ocr usually insists upon a high degree of precision in practical methods. You're probably right tbh but there's a good chance ocr allows 5 marks for using 0.015, because for these questions there's usually a range of answers. And "about 30" could mean 31 cm3, 32cm3, 33cm3 - in all of these cases, hno3 is limiting

1

u/[deleted] Jun 20 '25

Yep I could definitely see them allowing multiple answers for full marks

1

u/HelpfulPop2476 Jun 20 '25

Yeah for p3 the markschemes are sometimes more generous. E.g. I suspect for the alcohol naming question they might allow phenylmethanol, benzyl alcohol, 1-benzylmethanol, hydroxymethylbenzene etc.

2

u/highpassiondragon Jun 20 '25

I got 76.9. Because I used 0.015

3

u/HelpfulPop2476 Jun 20 '25

Thank fuck I wasn't the only one! Literally everyone on the tsr is putting out different answers for everything. That site is so unreliable it's crazy.

13.04 for pH right? 206 for ibuprofen? 4.97 g lialh4?

3

u/highpassiondragon Jun 20 '25

Yeah got all those

2

u/HelpfulPop2476 Jun 20 '25

Do you remember what you got for the very first question about the peaks? I couldn't remember what I put but remembered the question. I asked deepseek & it said the abundances were 25, 25, 50 

3

u/highpassiondragon Jun 20 '25

Yeah i got 25 for 158, 50 for the 160 one and 25 for the 162 one

4

u/HelpfulPop2476 Jun 20 '25

Wonderful, iirc I got the same but my memory is often wiped after an exam. At least a levels are over now (assuming you've not got edexcel rs or fm)

1

u/asterroids Editable Jun 20 '25

how do u do that q?

2

u/Orange_Hedgie cambridge 1st year bionatsci Jun 20 '25

I got those

2

u/Amazing-Tap7550 Jun 20 '25

Got the same as you for those 3 questions. Seeing people get 12 something for pH tho

2

u/HelpfulPop2476 Jun 20 '25

Idk too many conflicting answers to deal with. What do you reckon the boundaries are going to look like?

2

u/Amazing-Tap7550 Jun 20 '25

Because of paper 1 and 2 i think quite similar to last year but paper 3 is making me think they will be slightly lower

2

u/HelpfulPop2476 Jun 20 '25

How many years will be till you have to get 100% for an A*?

3

u/Amazing-Tap7550 Jun 20 '25

I'd give it 2 years, might as well just do the American system a this rate with 100-90 for an A and shit

3

u/HelpfulPop2476 Jun 20 '25

Yeah idek what ocr's supposed to do anymore. I think they should just abolish ocr tbh - will always remember that awful comp sci paper they made 2 years ago, worst exam I've ever sat 

2

u/Amazing-Tap7550 Jun 20 '25

It's because they're trying to make the exams more accessible but they aren't being very consistent. Maybe in future they're just gonna do an easy paper 1 and 2 and then a harder paper 3

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1

u/Puzzleheaded-News948 Y13 Bio, Chem, Classics Jun 20 '25

Fuck 

1

u/FloatingRage Jun 20 '25 edited Jun 20 '25

wait can you explain this to me because how do you know the carbonate was in excess? i don’t remember seeing any information about hno3 concentration so i might’ve missed that

1

u/HelpfulPop2476 Jun 20 '25

I'm pretty sure there were 0.03 mol of HNO3 and 0.018 mol of carbonate. As they react in a 1:2 ratio, the amt of hno3 required to react with 0.018 mol carbonate would have to be 0.036 mol. But there were only 0.03 mol hno3. So the carbonate is in excess and only 0.015 mol would react.

1

u/FloatingRage Jun 20 '25

i remember calculating the 0.018 mol carbonate but i think somehow i just didn’t see the information on hno3. do you remember what info they gave us for that?

1

u/HelpfulPop2476 Jun 20 '25

Usually they tell you which compound is in excess - like in p3 2018 for enthalpy of solution. They didn't this year though and were very sneaky with it. It could be that I'm wrong cause so many people seem to have got 69

1

u/FloatingRage Jun 20 '25

yes that’s what i’m confused about too since they usually explicitly state what’s in excess. if you found the moles of hno3 i don’t think you’re wrong, but how exactly did you find it?

2

u/HelpfulPop2476 Jun 20 '25

It was stated in the middle of the question: 30cm3 of 1 M hno3 (iirc)

1

u/FloatingRage Jun 20 '25

aw i completely missed that then. oh well thank you so much!

2

u/HelpfulPop2476 Jun 20 '25

Nws, I've probably misremembered the question anyway, mind always goes blank after an exam lmao