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

what did everyone get for the fatty acid question? i dont understand why people are saying the second one was right :/ even though there was unsaturated fatty acids there was nothing from the question that said they were trans fat. please can someone explain?

Reply 2461

lai812matthew

10

Original post by asunny465

what did everyone get for the fatty acid question? i dont understand why people are saying the second one was right :/ even though there was unsaturated fatty acids there was nothing from the question that said they were trans fat. please can someone explain?

the first one

Reply 2462

Can't think name

6

Original post by CharleaM

The one where you had to draw it and * the choral carbons? That one was [2] so I'd imagine one mark for the molecule and one for the correct chiral carbons.

Did u have to draw it on? I don't think I did that Fml

Reply 2463

Can't think name

6

Original post by CharleaM

The one where you had to draw it and * the choral carbons? That one was [2] so I'd imagine one mark for the molecule and one for the correct chiral carbons.

Did u have to draw it on? I don't think I did that Fml....I made so many silly mistake n I need an A

Reply 2464

lai812matthew

10

Original post by Can't think name

Did u have to draw it on? I don't think I did that Fml

yes

Reply 2465

GetOverHere

12

Original post by Can't think name

Did u have to draw it on? I don't think I did that Fml....I made so many silly mistake n I need an A

Yeah it said mark with an asterisk (*)

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Reply 2466

Can't think name

6

Original post by GetOverHere

Yeah it said mark with an asterisk (*)

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Fml thx hopefully I'll get the mark for the structure

Reply 2467

katiemckkk

1

the answer in the book is 8.3 times 10 to the minus 4 dm6mol-2s-1

I don't understand how that can be the answer???? Any help appreciated :smile:

Original post by katiemckkk

the answer in the book is 8.3 times 10 to the minus 4 dm6mol-2s-1

I don't understand how that can be the answer???? Any help appreciated :smile:

The book is either wrong or you're looking at the wrong answer

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Reply 2469

katiemckkk

1

hahah looks like mine has the wrong answer at least I'm not going mad, thanks very much!! :smile:

Original post by pineneedles

The book is either wrong or you're looking at the wrong answer

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Reply 2470

Emmax34

How many marks was it for drawing the triglyceride..?

Reply 2471

lukemurp890

5

Original post by Emmax34

How many marks was it for drawing the triglyceride..?

2 marks, one for the correct structure, and one for the chiral centres.

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Reply 2472

Rust Cohle

6

Original post by lukemurp890

2 marks, one for the correct structure, and one for the chiral centres.

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Correct

Mark scheme: https://goo.gl/gEi388

Reply 2473

johnjims828

1

Original post by GMQ

inb4 57 for A*

it won't be that high lol

Reply 2474

the traveller

1

since when have ocr ever made a jump that big in grade boundaries. people are predicting 54 for a star but that would mean an increase of 8 marks from last year. highest between consecutive exams so far is like 5. i also think people are underestimating the number of weird questions in the paper compared other papers. it doesnt feel 8 marks harder than last years paper.

Reply 2475

username1947027

8

Anyone remember whether the other factor for isomerism was based on just Cis isomerism or both cis-trans?

Reply 2476

mcdcph

4

Could someone please help me with calculating the pH of strong bases please? I understand that whenever you have water you have the H20 ⇌ H+ + OH- equilibrium set up and I understand that you can assume from this:
Ka = [H+] [OH-] and therefore .... Kw = [H+] [OH-]
---------------
[H20]

but how do you use this to work out the [H+] when you add a base? surelyby adding OH- you are using up some of the H+ to produce H20, these are in the same proportions so what [H+] or [OH-] decreases by H20 increases by therefore you in the case of...

[H+] [OH-]
---------------
[H20

] you're then dividing a smaller number by a bigger number so how does KW remain constant? surely it would decrease? meaning you can't use 1 x10-14 :frown:

(edited 7 years ago)

Reply 2477

the traveller

1

Original post by mcdcph

Could someone please help me with calculating the pH of strong bases please? I understand that whenever you have water you have the H20 ⇌ H+ + OH- equilibrium set up and I understand that you can assume from this:
Ka = [H+] [OH-] and therefore .... Kw = [H+] [OH-]
---------------
[H20]

but how do you use this to work out the [H+] when you add a base? surelyby adding OH- you are using up some of the H+ to produce H20, these are in the same proportions so what [H+] or [OH-] decreases by H20 increases by therefore you in the case of...

[H+] [OH-]
---------------
[H20

] you're then dividing a smaller number by a bigger number so how does KW remain constant? surely it would decrease? meaning you can't use 1 x10-14 :frown:

for a strong base the oh- conc is the same as the concentration of added alkali since all the alkali dissociates. therefore you use the kw equation. you know the conc of oh- and the value of kw(1.0x10-14) and so rearrange to find to H+ conc. then use ph= -log(h+) to get ur ph. dont worry about the concentration of of h+ and h20 decreasing and increasing it will only confuse you.