Aqa chem 4/ chem 5 june 2016 thread

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Reply 2480

ManOfJustTin

Original post by lahigueraxxx

what did everyone's graph look like for the hydrogen fuel cell?

I drew a straight line across? I thought there was a steady supply of reactants so

Reply 2481

EinHeimer

How many marks would I lose for forgetting to multiply the n of c204- by 10 and getting 9.44% ??

Reply 2482

Cadherin

Original post by hi-zen-berg

Good shout. How many marks of 7 do you reckon would be obtained if the divide by 3 part is missed out, to give a % purity of 35.33 (what i got)?

5/7 with ALL correct working shown.
-A1 for correct answer
-M4 for dividing by 3

Reply 2483

K2Cr2O7

Original post by lahigueraxxx

what did everyone's graph look like for the hydrogen fuel cell?

I put a straight horizontal line because there is a continuous supply of fuel. Anyone else put this ???

Reply 2484

thomaarrss

Original post by crillieswillies

Any idea how many marks I'd lose for getting delta G as -135000? I multiplied delta H by 1000 so delta H and delta S were in the same units :'(

if you put jmol-1 and not kjmol-1 you won't loose any... did you have to do it to 3 sig figures because i didnt?!?!

Reply 2485

idk97

Why is the purity 94 and not 50.7???/

Reply 2486

ravichauhan11

Original post by OloMed

For the hexaqua complexes questions, there was something like cr(h20)6 3+ going to X(g) and Y(s). What was X(g). CO2?

yep

Reply 2487

Rob1245

what was the born haber oxide?

Reply 2488

Hannahmollie98

Original post by Clarinet

The reaction was exothermic so if temperature increased, the reaction would shift to the left so solubility would decrease :smile:

The reactiom was endothermic so the reverse argument.

Reply 2489

Whitney997

What equations did you guys write for each electrode in the hydrogen-oxygen fuel cell question?

Reply 2490

username2280751

Absolute dream of a paper, got 120UMS for sure - hope this has made a load of people who thought they did awful on CHEM4 feel a bit better, could be the paper that brings it back for them!

Reply 2491

Rubato

Original post by hi-zen-berg

Good shout. How many marks of 7 do you reckon would be obtained if the divide by 3 part is missed out, to give a % purity of 35.33 (what i got)?

I did that too :frown:

I think error is carred forward to an extent if I remember correctly (:

Original post by cowie

I said increase as would be a in increase rate of reaction - I don't think reaction was reversible so le chateliers principle would be irrelevant? May be wrong

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The topic is called redox equilibria, of course le chateliers will be relevant.

Reply 2492

username1133132

Original post by randoms132

I got an answer for 35% too :frown:

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lol so did I :frown:

Reply 2493

cowie

Original post by K2Cr2O7

I put a straight horizontal line because there is a continuous supply of fuel. Anyone else put this ???

I drew two lines and wrote a caption for each..
One was horizontal and I mentioned fuel was constantly sullied
The other was a curve with decreasing gradient and I mentioned this was when fuel was not constantly suplied

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Reply 2494

DDan123

Original post by Saldudsjen123

I did I'm such an idiot!! :frown:

how many marks was that question?

If I'm not wrong I think there was 2 1 mark questions? I did the same thing so annoyed, but thankfully the rest of the paper was decent :smile:

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Reply 2495

Kay Fearn

Original post by zahraaj1

dissocation reactions are endothermic so the forward reaction is endo so the solubility increases when the temp increases as it shifts to the right (the endo reaction) because the solid ionic lattice (magnesium chloride) dissociates into its aqueous ions which increases the solubility. so idk how its a decrease haha

Pretty sure dissocation is when it turns into gaseous ions, this was talking about aqueous ions, the enthalpy of solution was negative

Reply 2496

username2280751

Original post by crillieswillies

Any idea how many marks I'd lose for getting delta G as -135000? I multiplied delta H by 1000 so delta H and delta S were in the same units :'(

You were supposed to divide delta S by 1000 to convert from JK-1Mol-1 to KJK-1Mol-1

Reply 2497

Osmium

Original post by crillieswillies

Any idea how many marks I'd lose for getting delta G as -135000? I multiplied delta H by 1000 so delta H and delta S were in the same units :'(

Both are allowed...

me toooo

Original post by Suits101

Half these because standard enthalpy means for one mole I believe (had to do it in a previous paper)

Product is less disordered than reactants/product is more ordered than reactants

It asked about the enthalpy change so I dont think you do it to one mole. I know the question you're talking about but that one had to specifically say 1 mole