AQA CHEM4 - 13th June 2012

theres actually two different answers, 4.48 using the moles in the calculation, 4.49 using the moles converted into concentrations then putting htem into the buffer calculations.. that question has come up in two past papers, they accept 2 different answers.

Reply 1381

Abbieastoria

7

Original post by Josh1993

4.48 is the correct answer.

Do you think I will lose any marks for rounding up to 4.49 cos it was

4.4848 which I rounded to 4.485
Then I rounded that to 4.49...

Worried now

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Reply 1382

callmenighthawk

2

god darn it, i wrote 0.0377dm^3 instead of 0.0378dm^3 :\

i don't think i'll get the mark for that :\

Reply 1383

Josh1993

Original post by Bubbles94

theres actually two different answers, 4.48 using the moles in the calculation, 4.49 using the moles converted into concentrations then putting htem into the buffer calculations.. that question has come up in two past papers, they accept 2 different answers.

They should be exactly the same.

If you have a fraction for e.g

24/10 / 15/10

this will be exactly the same as 24/15

Reply 1384

Josh1993

Original post by Abbieastoria

Do you think I will lose any marks for rounding up to 4.49 cos it was

4.4848 which I rounded to 4.485
Then I rounded that to 4.49...

Worried now

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

depends on how generous they are, you will lose 1 mark Max if you have shown all of your working.

Reply 1385

Bubbles94

8

Original post by Josh1993

They should be exactly the same.

If you have a fraction for e.g

24/10 / 15/10

this will be exactly the same as 24/15

thats what i thought.. but it's not, i had extra time left over so i did both versions of the question, one answer was 4.484 the other was 4.486 or something along those lines.. either way in past paper questions is does show that you can have two different answers.. to me it doesn't make sense but theres been evidence in the mark schemes so I guess its possible :L

Reply 1386

Astronomical

14

Original post by wibletg

A general rule of thumb? You've plucked examples from ONE (Jan 12) AQA paper. and in your words, another exam board (which is apparently irrelevant?)

Says the person that quoted a maths exam for a different exam board. :rolleyes:

Either you don't do any other A-levels, or you're challenged. Whichever it is, I care not, and I shan't reply to you again.

Reply 1387

Try

Original post by Abbieastoria

Do you think I will lose any marks for rounding up to 4.49 cos it was

4.4848 which I rounded to 4.485
Then I rounded that to 4.49...

Worried now

You'll lose one mark because 0.0048 doesn't round to 0.01, which is basically what you've done.

(edited 11 years ago)

Reply 1388

Astronomical

14

Original post by Bubbles94

thats what i thought.. but it's not, i had extra time left over so i did both versions of the question, one answer was 4.484 the other was 4.486 or something along those lines.. either way in past paper questions is does show that you can have two different answers.. to me it doesn't make sense but theres been evidence in the mark schemes so I guess its possible :L

Are you refuting the fact that 24/10 divided by 15/10 = 24/15? The answers are identical because the calculation is identical. Are you sure you didn't punch it into the calculator wrongly?

Reply 1389

wibletg

3

Original post by Astronomical

Says the person that quoted a maths exam for a different exam board. :rolleyes:

Either you don't do any other A-levels, or you're challenged. Whichever it is, I care not, and I shan't reply to you again.

You used Edexcel.

Thanks for confirming that I'm correct, and that you obviously have no idea what you're talking about :smile:

Reply 1390

Notsocleverstudent

4

An increasw in pressure favours sidewith more moles, eqn moves left. its C not B

Reply 1391

Josh1993

Original post by Bubbles94

thats what i thought.. but it's not, i had extra time left over so i did both versions of the question, one answer was 4.484 the other was 4.486 or something along those lines.. either way in past paper questions is does show that you can have two different answers.. to me it doesn't make sense but theres been evidence in the mark schemes so I guess its possible :L

Yeah they will allow both although 4.48 is a better answer. The reason why this discrepancy occurs is the inaccuaracies of the concentration. (people round off) :smile:

Reply 1392

Bubbles94

8

Original post by Astronomical

Are you refuting the fact that 24/10 divided by 15/10 = 24/15? The answers are identical because the calculation is identical. Are you sure you didn't punch it into the calculator wrongly?

no i swear to god and no i'm not refuting anything..? i'm just saying it is possible to have two different answers,using concentrations affects the way you round up the result..

http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM4-W-MS-JAN10.PDF
question 2cii) for example.. look at the right hand side for examiners comments.

i know chemistry. i'm not an idiot :L

Reply 1393

Abbieastoria

7

Original post by Try

You'll lose one mark because 0.0048 doesn't round to 0.01, which is basically what you've done.

I did write both I put
Ph=4.4848 therefore 4.49

So they were both there, oh well, didn't think I'd got that one right at all soon suppose its all a bonus even of I lose a mark

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