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Aqa chem 4/ chem 5 june 2016 thread

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Original post by 26december
I put H+ too but I don't think so because H+ isn't a reagent... So annoying :frown:


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What was the question asking for HCL?
Original post by Suits101
Did you say catalyst for last quesiton was Mn2+ and tick H2SO4?


Yes
Original post by OloMed
So X(g) = CO2 ?


Yes, i think it is.
lol and i the only idiot that got 49.3 for the percentage purity
Original post by Spectral
- Answer about pressure is correct because it does increase emf
- Answer about colorimetry is wrong because how does MnO4- bond with ligands??? It is not a transition metal, plus it's already a purple solution. Finally, data logger????? It's a colorimeter.

Well done for the pressure one, I'm sorry but I think you may only get 1 mark max for your answer about the colorimeter


Ahh not too bad then, I think i lost like 10 marks max on that paper including any silly mistakes I might have done so happy with the outcome :h:

I just hoped anything on calorimetry or spectrometry wouldn't come up because I never learned them fully but 3 marks isn't too bad.
Original post by Suits101
It said use your answer from the question above.

The answer was negative, hence the forward reaction is exothermic.

This same question (but with a different compound) came up in a previous paper.



-65.1 (divide it by 2 because it's standard meaning one mole, not two as question gave)


delta G got -65.1
for the pressure question on EMF i said that there's no change because there is equal number of moles on both side? :/ 100% wrong though, aren't i?
Original post by koolgurl14
What was the question asking for HCL?


The reagents to go from Cr3+ to Cr2+.
Ratio of C2O4^2- to MnO4^1 was 2:5,

There were 26.4cm3 of 0.02 moldm3 MnO4- = 0.000528 mols MnO4 therefore there was 0.00132 moles C2O4^2- in 25cm3 therefore 0.0132 moles in 250cm3,

There was 3 C2O4^2- per one mole of the salt therefore there were 4.4x10-3 moles salt

Mr K3(Fe(c2o4)3).3h20 = 491.1, Mass = moles x mr = 4.4x10-3 x 491.1 = 2.16g

Original mass = 2.22 therefore 2.16/2.22 * 100 = 94.4% purity.
Original post by Hopefulmedic15
Yeah I didn't resit chem 4 this year so I don't have that to compare to, and it's a bit inaccurate to compare chem 5 to chem 4 grade boundaries because they're completely different papers.


Yep, hopefully boundaries for unit 5 will stay roughly same. I need an A* in this paper atleast to make up for chem 4, Or else I will have to resit next year 😂😂😂😂


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What did everyone get for delta H and delta S and for the solution enthalpy question?
Original post by vinchy
delta G got -65.1


I did but I got it wrong because I said K = 298 + 50 which is 348 instead of 273 + 50!
Original post by DDan123
I wrote this too, but everybody saying it was increased :frown:


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The overall equation is:

H2 + 1/2 O2 ----> H2O

imcreasing conc of either H2 or O2, or increasing pressure, would all shift the equilibrium to the RHS, so EMF increases
Just to clarify - for the enthalpy and entropy calculations you had to take into account standard conditions. So you should have divided the equation by 2 to get so2 + 1/2o2 ----> so3 as it is the formation of 1mol of a compound. Then work it out
Original post by Maki.98
What did everyone get for delta H and delta S and for the solution enthalpy question?


Delta H = -98
Delta S = - 94.5
(divide your values by 2 because it said STANDARD enthalpy and question was for 2 moles)
Enthalpy of solution = -155
Original post by ssamarai
Said something very similar :smile:


Original post by Fibsy
It was 3 marks so I put:

MnO4- ions are purple
Filter light so only frequencies absorbed by the sample are let through.
The more concentrated the solution is, the less light it will let through.
Plot calibration graph with known concentrations and their absorbances. Use line of best fit to find concentration.

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WHAAAT! there was a backpage? i Don't remember doing this question, wasn't the 94% answer the final question on the paper?
Original post by Aerosmith
Just to clarify - for the enthalpy and entropy calculations you had to take into account standard conditions. So you should have divided the equation by 2 to get so2 + 1/2o2 ----> so3 as it is the formation of 1mol of a compound. Then work it out


oh for ****s sake, completely forgot
Original post by RME11
Ratio of C2O4^2- to MnO4^1 was 2:5,

There were 26.4cm3 of 0.02 moldm3 MnO4- = 0.000528 mols MnO4 therefore there was 0.00132 moles C2O4^2- in 25cm3 therefore 0.0132 moles in 250cm3,

There was 3 C2O4^2- per one mole of the salt therefore there were 4.4x10-3 moles salt

Mr K3(Fe(c2o4)3).3h20 = 491.1, Mass = moles x mr = 4.4x10-3 x 491.1 = 2.16g

Original mass = 2.22 therefore 2.16/2.22 * 100 = 94.4% purity.


im pretty sure that the original mass was 2.29
also how many marks do u think ill get if i got up to 0.0132 right and then carried the error
Original post by OloMed
The overall equation is:

H2 + 1/2 O2 ----> H2O

imcreasing conc of either H2 or O2, or increasing pressure, would all shift the equilibrium to the RHS, so EMF increases


Bingo!

Original post by Aerosmith
Just to clarify - for the enthalpy and entropy calculations you had to take into account standard conditions. So you should have divided the equation by 2 to get so2 + 1/2o2 ----> so3 as it is the formation of 1mol of a compound. Then work it out


Finally someone who agrees.
Original post by Agent R5
WHAAAT! there was a backpage? i Don't remember doing this question, wasn't the 94% answer the final question on the paper?


Only worth 3 marks.

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