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# Ocr gateway CHEM 4 5 6 markscheme

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1. (Original post by Wolfram Alpha)
There's 0.16g of hydrogen, what's the volume of this has at RTP? I got 300,000 but am certain my answer is incorrect.
Pretty sure it was 1920cm^3

This is because 1mole of H2 = 24000cm^3 = 2g

1g H2 = 12000cm^3

0.01g H2 = 120

0.16g H2 = 1920

But I may be wrong

HAVING SAID THAT

I put 3840cm^3

This is because (24000/100) * 16

Have a look here: http://www.thestudentroom.co.uk/show....php?t=4176844
2. (Original post by Wolfram Alpha)
Argh, I divides rather than multiplied!
Oh no! How many marks was it? I'm sure you'll definitely get 1 at least.

What I did was mass/mr = mols
0.16g/2 (H2 =1×2)
This got me 0.08 mols
1 mol = 24000cm^3
Divide 24000 by 12.5 bc 1/12.5 = 0.08

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3. (Original post by Gamer_44)
The equation = volume of acid x concentration of acid = volume of alkali x concentration of alkali.

What I don't understand is where it says you have to use the 'end point'.

I understand what you mean but the volume of acid was continued beyond the end point?
the end point of a titration is the volume needed for it to fully neutralise, so it's the pretty-much vertical bit on a pH curve
not 100% but i think you use that value because when you actually do a titration you stop when the indicator changes colour and you've neutralised the solution and record that value
4. (Original post by Vanilla Cupcake)
the end point of a titration is the volume needed for it to fully neutralise, so it's the pretty-much vertical bit on a pH curve
not 100% but i think you use that value because when you actually do a titration you stop when the indicator changes colour and you've neutralised the solution and record that value
Yea I understand what you saying but checking previous mark schemes the good thing is you will get marks for just having the correct formula. As its probably 3marks for calculation and 3 marks for the other part of the question.
5. (Original post by Gamer_44)
Yea I understand what you saying but checking previous mark schemes the good thing is you will get marks for just having the correct formula. As its probably 3marks for calculation and 3 marks for the other part of the question.
You were supposed to add the formula?
6. (Original post by Vanilla Cupcake)
the end point of a titration is the volume needed for it to fully neutralise, so it's the pretty-much vertical bit on a pH curve
not 100% but i think you use that value because when you actually do a titration you stop when the indicator changes colour and you've neutralised the solution and record that value
I agree with you. The whole point of the experiment is to find out the amount of acid needed to neutralise the alkali. The rest of the acid had no use. Your calculating the concentration of acid needed to neutralise the alkali. By adding the other 20cm^3, your saying that the acid was twice as dilute as it was actually when neutralising if you get me

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7. (Original post by mxskaan)
Oh no! How many marks was it? I'm sure you'll definitely get 1 at least.

What I did was mass/mr = mols
0.16g/2 (H2 =1×2)
This got me 0.08 mols
1 mol = 24000cm^3
Divide 24000 by 12.5 bc 1/12.5 = 0.08

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It was 2 marks. Where did you get 12.5 from? I just did 24000/0.08...but I think I rearranged the equation incorrectly.
8. (Original post by Wolfram Alpha)
It was 2 marks. Where did you get 12.5 from? I just did 24000/0.08...but I think I rearranged the equation incorrectly.
Aren't you supposed to convert 24000cm3 into dm3 ???????
9. (Original post by ellamoon_22)
steorotypical
¬¬
10. (Original post by Wolfram Alpha)
It was 2 marks. Where did you get 12.5 from? I just did 24000/0.08...but I think I rearranged the equation incorrectly.
Yes you could alternatively do 0.08*24000.

(Original post by happiness12)
Aren't you supposed to convert 24000cm3 into dm3 ???????
11. (Original post by happiness12)
Aren't you supposed to convert 24000cm3 into dm3 ???????
The units in the answer area were cm3
12. (Original post by happiness12)
No because this paper is worth more than the other paper

Paper 1 ums
A* = 126
Paper 2 ums
A* = 144
Coursework ums
A* = 90

To get an A* overall you need 360 ums points
You can get over 126 in paper 1 and over 90 in paper 2.
Those values are the minimum for A*.

Paper 1 /140
Paper 2 /160
Paper 3 /90

It's harder with chemistry to get the cap but in biology and physics you only need to be in the mid 60s to get 160/160 on paper 2/

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