OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

Unit 4 as in F324?
F324 is a really nice paper as long as you know your stuff. Make sure you know the spec inside out and then practice papers! Practice lots of NMR and Synthesis. Make sure you know which groups can react with which substances so you can apply this in synthesis.

what do you mean with synthesis? like polymers? :colondollar:

Reply 301

alow

19

Original post by ranz

what do you mean with synthesis? like polymers? :colondollar:

Synthesis as in methods to synthesise particular groups with particular stereochemistry.

E.g. to synthesise ethanol from ethanal you would use something like sodium borohydride.

There aren't many you have to remember for A Level.

Reply 302

zirak46

8

Hey guys, if a question is asking for partial pressure of a molecule in an equilbrium, what does that mean?

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Reply 303

chanda01

13

Original post by ranz

what do you mean with synthesis? like polymers? :colondollar:

Synthesis is all your organic reactions etc. You could be given a molecule in the exam, or maybe two, and asked to make one out of the other and display a series of steps to get to the end molecule by including any intermediates, reagents and conditions. Sometimes they walk you through it like they did on last years' paper, or sometimes they just put in a 5-7, maybe more, marker question in and you just have to do from beginning to end yourself.

Reply 304

ranz

5

Original post by chanda01

Synthesis is all your organic reactions etc. You could be given a molecule in the exam, or maybe two, and asked to make one out of the other and display a series of steps to get to the end molecule by including any intermediates, reagents and conditions. Sometimes they walk you through it like they did on last years' paper, or sometimes they just put in a 5-7, maybe more, marker question in and you just have to do from beginning to end yourself.

ah yess, like producing azo dyes, im struggling with naming 😭 in unit 5 im struggling with transition metals, that last qs, i till now dont know what colours and reactions im meant to know of t.m ive learnt a bunch but worried im missing one out

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Reply 305

AqsaMx

5

What metal ion forms a colourless complex ion [XCl4]3-

Reply 306

AqsaMx

5

If you're given a compound e.g (NH4)2PtCl6
How to work out the complex ion present?

Reply 307

cr7alwayz

8

Does anyone know how to do F325 June 2015 question 4eiii?

After calculating the moles of magnesium, I don't understand how to get the next 2 marks, what does the mark scheme mean by calculating the moles/concentrations for C2H5COOH and C2H5COO Can anyone explain how to do this question.

Reply 308

pineneedles

14

Original post by cr7alwayz

Does anyone know how to do F325 June 2015 question 4eiii?

After calculating the moles of magnesium, I don't understand how to get the next 2 marks, what does the mark scheme mean by calculating the moles/concentrations for C2H5COOH and C2H5COO Can anyone explain how to do this question.

Hey, so you add 0.25 moles of magnesium to the buffer and the following reaction takes place:
Mg + 2C2H5COOH > (C2H5COO-)2Mg2+ + H2
The stoichiometric ratio of magnesium to the weak acid and salt is 1:2 so (0.25 * 2) moles of the weak acid are 'used up' and (0.25 *2) moles of the salt are produced. I think in the question, the buffer has equal quantities of the salt and weak acid, so the new ratio of HA/A- is 0.50/1.50

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Reply 309

cr7alwayz

8

Thanks, I think I understand what you mean. I've never seen a buffer question like that one before, need more practice with ones like that

Reply 310

bakedbeans247

20

Anyone have the 2015 papers? Thanks in advance!

Reply 311

ranz

5

Original post by marioman

Not sure if these have been posted yet.

June 2015 F321: Paper | Mark Scheme
June 2015 F322: Paper | Mark Scheme
June 2015 F324: Paper | Mark Scheme
June 2015 F325: Paper | Mark Scheme

here the papers

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Reply 312

AqsaMx

5

Can anyone explain this pls

Reply 313

thad33

12

Original post by AqsaMx

Can anyone explain this pls

Your first answer looks right to me.

Henderson-Hasselbalch equation:

pH = pKa + log(A-/HA)

3 = 4 + log(A-/HA)

log(A-/HA) = -1

So the ratio must be 1/10 as 10^-1 = 1/10

Your second answer would be the opposite so 10/1 as you need log(A-/HA) = 1.

I think anyway, I could be missing something.

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Reply 314

AqsaMx

5

Original post by thad33

Your first answer looks right to me.

Henderson-Hasselbalch equation:

pH = pKa + log(A-/HA)

3 = 4 + log(A-/HA)

log(A-/HA) = -1

So the ratio must be 1/10 as 10^-1 = 1/10

Your second answer would be the opposite so 10/1 as you need log(A-/HA) = 1.

I think anyway, I could be missing something.

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Thanks!

Reply 315

AqsaMx

5

Can someone explain why the reaction between phenol and Na is classed as a redox/reduction reduction, is it become the Carbon oxidation number decreases??