OCR B F335 - Chemistry by Design - 13th June 2012

why did maleic acid have two pKa values?

Guessed it was one value for each enantiomer

I said because it had two carboxylic acid groups which could disassociate to different extents in different conditions :s but it was tenuous at best

It's because there are two ways it can dissociate.

http://uk.answers.yahoo.com/question/index?qid=20080715132737AAnPQyS

Reply 1201

avataraang

6

Original post by Princess Kawaii

Oh just remembered one question it was about turning the aldehyde into carboxylic acid and it asked why this test will not distinguish between the two. What did u guys write for that?

I think I wrote something along the lines of that the aldehyde will be oxidised to the carboxylic acid. So therefore both solutions will be green and you cannot tell the difference since they will both be the same colour

Reply 1202

Lilgig

Original post by user3456

3) Prove that oxygen concentration is ...
Work out concentration of NO2

4) Work out the Kc for the above equation
5) Using the above information work out the concentration of (cant rememeber..)?
6) What effect does increasing the temperature have on the equilibrium constant
7) What effect does high pressure have on the equilibrium constant

sorry if i've got any wrong bt that seems to be how i remember it!

Sounds good to me :smile:

know anymore as I feel I may have missed a question out :s

Reply 1203

georgie94

Original post by Princess Kawaii

Oh just remembered one question it was about turning the aldehyde into carboxylic acid and it asked why this test will not distinguish between the two. What did u guys write for that?

I said it was a test for the C=O group which is present in both substances... I was clutching at straws there..

Reply 1204

Princess Kawaii

OP

15

what other stupid/hard questions were there?

Can't remember now...but I need to know to put my mind at rest :biggrin:

Reply 1205

Lilgig

Original post by Princess Kawaii

what other stupid/hard questions were there?

Can't remember now...but I need to know to put my mind at rest :biggrin:

Same here!!!

Reply 1206

littlesteelo

That has just completely f***ed up my chances of getting my place now. I was borderline A before, but this has probably dragged it down to a C, and I need at least a B. Thanks a lot, OCR.

Reply 1207

tania<3

15

Original post by georgie94

I said it was a test for the C=O group which is present in both substances... I was clutching at straws there..

I said the other molecule had a OH group which would oxidize to make a ketone, so you'd see the same colour change as your would for the aldehyde. So physically you'd see no difference

Reply 1208

Birterillo

5

[QUOTE="sunshinesmile10;38093440"]

Original post by Birterillo

Errrrm, what did the question actually ask you to do?

state the molecule that would be needed to make (tri phenyl methane? ok not sure if this is the name) in addition to the alcl3 catalyst
do you remember it now???
maybe your too traumatised :smile:

( i think i am)

I might do. Surely i wouldnt just not answer a question half way down a page? Maybe i would... Haha I actually thought the paper was ok generally though. There were hard bits all over the place but if you think of all the bits that you had no problems with I'm sure you'd all not think it went quite as badly. It's easy to concentrate on what you didn't know, though. I thought I was probably at a slight advantage having done unit 2 resit this summer. With it being a synoptic paper. Like the orange to green thing was all a part of that module. Anyway, I'm sure a lot of you will be surprised at how well you've actually managed despite having a hard paper!

This was posted from The Student Room's iPhone/iPad App

Reply 1209

csefton3

What did everyone put for the penultimate question? Entropy, and why the entropy change of system is positive for dissolving reactions? And why the entropy change of system is negative when Ca2+ ions are involved? I think i got those two marks wrong :/ along with hundreds of others ofc.....

This was posted from The Student Room's Android App on my GT-I9100

Reply 1210

littlesteelo

I think what makes it worse is that the questions which you know and can answer straight away you tend to forget about, but the harder ones stick in your mind. I am sat here now thinking of more and more questions which I have failed. Chemistry is not even relevant to my degree, and it looks like it will be the one thing which will bring me down.
Does anybody know what the grade boundary for a B will be?

Reply 1211

bssjonny

12

Original post by csefton3

What did everyone put for the penultimate question? Entropy, and why the entropy change of system is positive for dissolving reactions? And why the entropy change of system is negative when Ca2+ ions are involved? I think i got those two marks wrong :/ along with hundreds of others ofc.....

This was posted from The Student Room's Android App on my GT-I9100

I put something along the lines of:
When most ionic substances dissolve there is an increase intropy since there are ways for the water molecules and ions to be arranged to so more disorder
Ca2+ ions can atrract water molecules very strongly forming ion - dipole bonds
The water molecules arrange themselves around the Ca2+ ion and so become ordered. Less disorder and so there is a decrease in entropy

Reply 1212

Tomatochuckers

18

My reaction to the paper:

Reply 1213

Tomatochuckers

18

Original post by littlesteelo

X

Around the 70-73 mark out of 120.

Its such a huge paper, packed with my mistakes :frown:

Reply 1214

Hasi.ali

Original post by Tomatochuckers

Around the 70-73 mark out of 120.

Its such a huge paper, packed with my mistakes :frown:

Ok.

Reply 1215

DipolarBitch

**** happens. :smile:

Reply 1216

Hasi.ali

Original post by DipolarBitch

**** happens. :smile:

If you say so...

Reply 1217

DipolarBitch

Original post by littlesteelo

I think what makes it worse is that the questions which you know and can answer straight away you tend to forget about, but the harder ones stick in your mind. I am sat here now thinking of more and more questions which I have failed. Chemistry is not even relevant to my degree, and it looks like it will be the one thing which will bring me down.
Does anybody know what the grade boundary for a B will be?

They won't decide the grade boundaries until all of the papers have been marked and they know how badly we all did and how they screwed with all of our entire lives.

Reply 1218

DipolarBitch

I hope that after that exam, the writers for the OCR examining board get Seneca Crane'd.

Reply 1219

Tomatochuckers

18

Original post by Hasi.ali

If you say so...

Well done for not finding it hard, but what was the point of commenting there lol

Original post by DipolarBitch

They won't decide the grade boundaries until all of the papers have been marked and they know how badly we all did and how they screwed with all of our entire lives.

no- grade boundaries dont really vary. The past 4 papers has only seen a difference of 3 raw marks in the grade boundaries unfortunately.

OCR B F335 - Chemistry by Design - 13th June 2012

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