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AQA A2 Chemistry - CHEM5 22/01/13

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Can anyone help me when it comes to writing the conventional representation for a cell. Teachers literally told us to skip those questions because they don't even know how to do it. Cant find a proper explanation in any of the books

All I know is l is change in phase, ll is salt bridge, and that you use pt on each end if elements are not metallic

Reply 41

Anjna

Original post by Beth_L_G

when you draw conventions
1) the half cell with the more negative potential goes on the left
2) the oxidised forms go in the centre

e.g. zn^2+ + 2e- => Zn (-0.76V)
cu^2+ + 2e- => Cu (0.34V)

Zn|Zn^2+||Cu^2+|Cu

Reply 42

phil1093

ok im struggling with how in the jan 12 paper, question 8 e)i) it says, right the equation for en + an aqueous solution of aluminium chloride. and then ii) en + aqeous solution of colbalt (ll) sulpate… so I stupidly (apparently) tried to use [AlCl4]- and in ii) I used CoSO4… and basically got them both wrong as apparently youre supposed to use [Al(H2O)6]3+ and [Co(H2O)6]2+ which I wouldve been able to do (had I remembered that en subsitues 2 H2Os…)
Basically, how come I shouldve used the [Al(H2O)6]3+ and [Co(H2O)6]2+ when thats not what it said? or did it and I am being daft here? should I have known to use [Al(H2O)6]3+ and [Co(H2O)6]2+ since its aqueous.. Is there a way I can know when to use it tomorrow?

Much appreciated thanks in advance.. :smile:

Reply 43

Anjna

can anyone help me with 1c and 3b june 2011 paper please? thanks

(edited 11 years ago)

Reply 44

Anjna

anyone help me understand how you work out lattice enthalpies ect using values from born haber cycles? its really confuses me :s-smilie:

Reply 45

YWArtist

Right june 2012 paper
Q6D part 1
I have no clue how they get ratio 3:5?
I got 2:5
The calculation after is straight forward I just don't know how they got the ratio

Reply 46

chazza95

Original post by YWArtist

Right june 2012 paper
Q6D part 1
I have no clue how they get ratio 3:5?
I got 2:5
The calculation after is straight forward I just don't know how they got the ratio

you have to combine the moles of Fe and ethaindioate so it's becomes 5:3! :smile:

Reply 47

Chatirito_MUFC

Original post by Anjna

erm you could talk about how hydrogen is highly flammable so it has to be handled carefully when it is stored or transported. and also how the process isn't carbon neutral? i think :s-smilie:

Thanks. I think that should be one!

Reply 48

phil1093

Original post by YWArtist

Right june 2012 paper
Q6D part 1
I have no clue how they get ratio 3:5?
I got 2:5
The calculation after is straight forward I just don't know how they got the ratio

Do you have a mark scheme?!

Reply 49

Beth_L_G

Good luck today everyone :smile:

Anyone got any last minute tips?

Reply 50

Beth_L_G

How did everyone find that?

Reply 51

cloesmith

Did anyone else have this today and thought it was quite hard!?

Reply 52

Beth_L_G

First question was horrible but though it wasn't too bad apart from that

Reply 53

Chatirito_MUFC

Think the grade boundary might be a little high for this one. Hope not!

Reply 54

popnit

Feel like I've been violated..awful awful awful paper.

Posted from TSR Mobile

Reply 55

Beth_L_G

Apart from the first question I don't think it was as bad as some past papers

Reply 56

DCLXVI

What was the answer to the last question?

I think the question was what was the minimum volume of 5moldm^-3 H₂O₂ that is required to oxidise 9.87? grams of CoSO₄.7H₂O.

Was it this:

The reaction was a 2:1 ratio: 2[Co(NH₃)₆]²⁺ + H₂O₂ --> 2[Co(NH₃)₆]³⁺ + 2OH^-So moles of Co²⁺= 0.035
Moles of H₂O₂ = 0.018
Volumes is then = 3.52cm³?

Also the question about hydrogen and oxygen going to gaseous water, what was the temperature at which the reaction was not feasible? That question did not make sense to me, it asked for the temperature ABOVE which the reaction was NOT feasible. I thought any temperature above the Temp where ∆G = 0 will make ∆G negative therefore the reaction would be feasible.

(edited 11 years ago)

Reply 57

PancreaticJuice

it was difficult
what was the last 5marker?
and some questions were horribly worded

Reply 58

Beth_L_G

Original post by DCLXVI

What was the answer to the last question?

Also the question about hydrogen and oxygen going to gaseous water, what was the temperature at which the reaction was not feasible? That question did not make sense to me, it asked for the temperature ABOVE which the reaction was NOT feasible. I thought any temperature above the Temp where ∆G = 0 will make ∆G negative therefore the reaction would be feasible.

That depends on if entropy is positive or negative

Reply 59

NimbusCumulus

unofficial mark scheme someone?

ILL TRY:

Q-1a Define enthalpy of bond dissociation referring to chlorine
b Why is the enthalpy of atomisation of chlorine half of enthalpy of bond dissociation
c Write down an equation with state symbols which has the same value of enthalpy of CLF formation ??
d Calculate bond enthalpy of Cl - F?
e Calculate enthalpy of formation of ClF3?
f Why cant we find the bond enthalpy of Na - Cl in data books?