AQA chemistry 3t (p13) ISA help please

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science2
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just doing some past papers on the chem 3t (p13) isa, JUNE 2013 at the moment,

stuck on question 5a, any help on it please
(I'm using an average titre of 29.00 cm^3 for my answers)

I tried working it out by 1st working out the moles of Y using Q.4 x 5.00.
and then using the answer (moles) by dividing the mass 71.5 by the answer(moles).
If that makes sense. Obviously wrong because they are working it out differently in mark scheme so I think my answer would be wrong the way I worked it out.

Link to isa paper & mark scheme:

http://filestore.aqa.org.uk/subjects...TEST-JUN13.PDF

http://filestore.aqa.org.uk/subjects...W-MG-JUN13.PDF
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Puddles the Monkey
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Hey there,

I'm just going to move this in to the Chemistry forum for you. You might be able to get some more responses there.
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Mr Lawlor
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What they have done is:

Step 1: calculate the concentration in gdm-3.
mass/volume = 71.50/5 = 14.3 gdm-3

Step 2: Divide the mass concentration by the mole concentration to get the Mr.
mass conc / mole conc = 14.3/Q4 = Mr

Proof: (mass/volume) / (moles/volume) = mass/volume = Mr

Your method is equally as valid and you would have got the marks. I would have done it your way too.

Hope this helped,

Mr L

(@MrL_Chemistry)
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