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Aqa chem 4/ chem 5 june 2016 thread

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Original post by K2Cr2O7
Yes, i think it is.


Thank u. Not sure whether they asked for X(g) or Y(s)? I remember putting CO2 as an answer
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


Ah, do you remember how many marks that was worth??


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Reply 2582
Avatar for tbh12
tbh12
9
For the colorimetry question I put this but am not sure if it is correct.

1. Obtain solutions of Fe2+ at different concentrations and add these solutions to MnO4- one by one.
2. Keep total volume of resultant solution the same by adding H2O as necessary
3. Use colorimeter to detect when resultant solution turns just purple/pink due to excess Mn2+
4. In this solution the ratio of Fe2+ moles to MnO4- is 5:1.
5. Use the moles and concentration of Fe2+ to work out the moles and concentration of MnO4-
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?


Yeah there was one more question after that
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


what??? Ffs
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.


I got this after a while of crossing most of my working out. The divide by three was the worst part - i kept getting answers more than 100% .
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?


No!! There was one more Q.!
I got 50.7% for the purity, how many marks would I have dropped here ??????
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


but the pressure of just the oxygen not the hydrogen was increases so surely this only effects the equilibrium of 2H2O + O2 4e -> 4OH-
How many marks do you think you would get for the standard enthalpy of formation and entropy and that if you forgot to divide?
Surely 2/3 for each part??



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Anyone confirm?

SA has no effect on emf

Environmental advantage: doesn't need to be electrically recharged

Why not carbon-neutral: hydrogen is produced by electrolysis which requires electricity that's produced from combustion of fossil fuels releasing CO2
Original post by DDan123
Ah, do you remember how many marks that was worth??


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I'm guessing 2 max
Original post by DDan123
I wrote this too, but everybody saying it was increased :frown:


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Was 02 the positive or negative electrode?
Original post by Suits101
Anyone confirm?

SA has no effect on emf

Environmental advantage: doesn't need to be electrically recharged

Why not carbon-neutral: hydrogen is produced by electrolysis which requires electricity that's produced from combustion of fossil fuels releasing CO2


I put for the environmental advantage that it doesn't release CO2 :frown:
Original post by m_ermaidmotel
I got 50.7% for the purity, how many marks would I have dropped here ??????


i got this i think only 2 marks dropped hopefully!
Original post by Suits101
Anyone confirm?

SA has no effect on emf

Environmental advantage: doesn't need to be electrically recharged

Why not carbon-neutral: hydrogen is produced by electrolysis which requires electricity that's produced from combustion of fossil fuels releasing CO2


I put environmental advantage is that it doesn't produce carbon emissions??? Something like that

And not carbon neutral because hydrogen may be produced from burning fossil fuels


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Reply 2596
Avatar for cowie
cowie
7
Original post by Suits101
Bingo!



Finally someone who agrees.


I SWEAR FUEL CELLS AREN'T REVERSIBLE THOUGH?! Which would mean equilibrium wouldn't shift as there isn't one and the emf would increase due to increase in pressure increasing rate of reaction?


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Original post by DDan123
Ah, do you remember how many marks that was worth??


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3 marks.

Original post by 26december
How many marks do you think you would get for the standard enthalpy of formation and entropy and that if you forgot to divide?
Surely 2/3 for each part??



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Drop one mark on each question using these values, so drop 3 overall out of 9
(this error happened on previous papers, one mark was dropped for each answer not divided by 2)
Original post by Suits101
Anyone confirm?

SA has no effect on emf

Environmental advantage: doesn't need to be electrically recharged

Why not carbon-neutral: hydrogen is produced by electrolysis which requires electricity that's produced from combustion of fossil fuels releasing CO2


for environmental advantage i think that it should be that there are no carbon emissions
Original post by 26december
How many marks do you think you would get for the standard enthalpy of formation and entropy and that if you forgot to divide?
Surely 2/3 for each part??



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I hope so, just seems so sneaky ffs lol


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