AQA A2 CHEM4 &amp;amp; CHEM5 June 2015 [official discussion thread]

Original post by ThatMadClown

just rearrange the formula so the new products are at the top, they've just swapped the reactants and products so rearranging the formula to get the new products at the top means you can find kc :smile:

Thank you!

Reply 583

Original post by _Caz_

I think you have to follow the mechanism through again but with the 3- hydroxybutanal as one of the reactants and ethanal as the other one. I've attached a picture of my working if that helps. (Ignore the scribble on the last line sorry its a bit messy)

Posted from TSR Mobile

Hey I was just looking at this again and I thought I got it but I'm still confused :frown:

So step 1 was identical to the step 1 they did. Then how did you know how to do the following steps?

Reply 584

LookIts_Liam

Original post by adorablegirl1202

Great, I feel good on that! Another question heading your way,http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-QP-JUN11.PDF how do we do 3h? Initially i thought it would be the reciprocal but it isn't.

Why do you say it isn't the reciprocal? I'm fairly sure it should be

Reply 585

_Caz_

Original post by adorablegirl1202

Hey I was just looking at this again and I thought I got it but I'm still confused :frown:

So step 1 was identical to the step 1 they did. Then how did you know how to do the following steps?

It's the same as the first mechanism but replacing one of the ethanals with the 3hydroxybutanal. So the c=o bond opens up on the 3hydroxybutanal and an ethanal joins on to it rather than it happening between two ethanals. Because it says further substitution I just assumed that it would be another ethanal adding to the previous product. I'm not sure what it means by trimer though. Looking back on it I think I missed a hydrogen on the product as well (sorry) :frown:

I'm not sure if this helps at all.

Reply 586

Original post by LookIts_Liam

Why do you say it isn't the reciprocal? I'm fairly sure it should be

You're completely right, I just checked again and I think I was plugging in the wrong value- I couldn't understand for the life of me yesterday what mistake I was making but now it's apparent. Thanks :smile:

.

Reply 587

Original post by _Caz_

It's the same as the first mechanism but replacing one of the ethanals with the 3hydroxybutanal. So the c=o bond opens up on the 3hydroxybutanal and an ethanal joins on to it rather than it happening between two ethanals. Because it says further substitution I just assumed that it would be another ethanal adding to the previous product. I'm not sure what it means by trimer though. Looking back on it I think I missed a hydrogen on the product as well (sorry) :frown:

I'm not sure if this helps at all.

It does help, thank you! :smile:

Reply 588

_Caz_

Original post by randlemcmurphy

For these type of questions you will always have data to refer to. Just make sure you read all the electrode potentials so you can see whether further oxidation occurs. To be honest I have been thinking of the point you brought up as well. I'm going to ask my teacher next week.

I'll ask as well :smile:

let me know if you find out anything

Posted from TSR Mobile

Reply 589

hukdealz

anyone know where to find the june 2014 CHEM5 question paper?

would be massively grateful

Reply 590

Cobalt_

21

Original post by _mistyeye

I've basically taught myself over half the chemistry course this year as my school hasn't been able to provide me a teacher... and I have a basic understanding of it all but I really don't understand buffer calculations. I understand the theory behind buffers but whenever a question comes up asking to calculate the pH of buffers etc I just don't get it. I've tried reading textbooks that explain how to do it hundreds of times but I still can't do it. Does anyone have a really simple method explaining how to do them?? As they're normally 6 mark questions and that's quite a lot of marks to drop etc :/

Yeh, I might actually make a video before the CHEM4 exam going over all the types of buffer questions you can get!
If not, ill explain them to you over PM c:

Reply 591

Cobalt_

21

Original post by _Caz_

Hi

could you help me with this please? The correct answers are in red on the picture. I just don't understand how they got that answer. I've attached the data table the question refers to as well.

Thanks :smile:

Posted from TSR Mobile

Dont worry!
Vanadium isnt on the new specification!, It was on the old one and they commonly asked questions about it.

I remember my teacher clearing this up

Reply 592

_Caz_

Original post by Cobalt_

Dont worry!
Vanadium isnt on the new specification!, It was on the old one and they commonly asked questions about it.

I remember my teacher clearing this up

Oh okay! Thanks for letting me know :smile:

Posted from TSR Mobile

Reply 593

shloke123

1

anyone got chem5 2014 paper?

Reply 594

hukdealz