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Chem5 June 2014 Unofficial Mark Scheme

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Original post by Kim Moffatt
For the colour complexes questions I wrote OH- and NH3 and I think Cl- instead of NaOH and HCl

Will I loose the marks for this please???

I did the same, I am hoping they are nice and give us the mark because in theory it's correct.
Original post by biojay_
They asp asked why can't the cell be recharged? Can't remember full question but I wrote because the reaction is not reversible? Also got -0.02 for the value of delta S for the question where -5=-9-(298xS)

You forgot to x1000 though to put it into the correct units as Jk-1 mol-1 not KJ K-1 mol-1?
That's what I did, but not sure if it's 100% correct.
For the question "Why Fuel cell is better than internal combustion engine?"

I wrote because water is the only waste product formed and no CO2, is that right and would I get the marks?
(edited 9 years ago)
Original post by crazylyt
The qiestion has said need to be given formula, definitely!


Does it matter though if I wrote 'hydrochloric acid'!!?? bloody hell!!! help!!!
anyone know where to find the question paper? It would hugely help for revision!
Can someone run through the mass question at the end? Don't see how the mass is 5. something grams PLEASE!!!
Original post by harrietgrace144
Can someone run through the mass question at the end? Don't see how the mass is 5. something grams PLEASE!!!

what answer did you get?

remember the ratio of moles is 1:6 and you have to scale your answer up by 10
Original post by hukdealz
what answer did you get?

remember the ratio of moles is 1:6 and you have to scale your answer up by 10


Yeah I found the moles of the dichromate
Times that by 6 and then times that by 10 and then did moles x Mr for the iron? Answer i got was 1.06 g
Original post by harrietgrace144
Yeah I found the moles of the dichromate
Times that by 6 and then times that by 10 and then did moles x Mr for the iron? Answer i got was 1.06 g


n(K2Cr2O7)=c x v=0.0213 x 0.015 = 3.195x10-4

multiply by 6 because ratio is 1:6
multiply by 10 to get full 250cm^3 moles
=0.01917

m=n x Mr=0.01917 x 277.9= 5.33g


easy 5 marks (in theory)
Original post by harrietgrace144
Yeah I found the moles of the dichromate
Times that by 6 and then times that by 10 and then did moles x Mr for the iron? Answer i got was 1.06 g

you're right up until the very last point. You've used the Mr of Fe, but you need to use the entire Mr of FeSo4.7H20 because you're trying to find out how much FeSo4.7H20 there is in the sample of X.
Original post by hukdealz
n(K2Cr2O7)=c x v=0.0213 x 0.015 = 3.195x10-4

multiply by 6 because ratio is 1:6
multiply by 10 to get full 250cm^3 moles
=0.01917

m=n x Mr=0.01917 x 277.9= 5.33g


easy 5 marks (in theory)


ahh thank you! I was multiplying by just the iron Mr

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