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AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

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I'm hoping we don't get a load of synoptic stuff.

Bet we will though.
Original post by Luke0011
I'm hoping we don't get a load of synoptic stuff.

Bet we will though.


Has there been a lot in the past papers? Don't remember much being in the June 2010 and Jan 11, but I may be wrong.
Original post by InItToWinItGetIt?
Has there been a lot in the past papers? Don't remember much being in the June 2010 and Jan 11, but I may be wrong.


Nah there hasn't, that's what makes me think we will :P
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sd2011
could someone explain how the colorimetry works please?
need help on specimen paper question 3bi how did they get vo2+??
Reply 365
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jimmy303
1
Original post by jamest92
I'd say the answers are wrong, from the way its set up it should be -1.61


How is it wrong?

Just because the beaker with the zinc electrode is on the left doesn't mean it's on the left in the conventional representation. You could just as easily slide the beaker on the table so that it's on the right...

hey_its_nay
x


Learning it as RHS-LHS is very risky tbh.

Learn it as:

emf = most positive electrode potential - most negative electrode potential.

In 2b i)

Mg/Mg2+ has a E value of -2.37
Zn/Zn2+ has a value of -0.76

Mg/Mg2+ is most negative
Zn/Zn2+ is most positive

Thus emf = -0.76 - (-2.37)
=1.61V
Original post by Luke0011
Nah there hasn't, that's what makes me think we will :P


But is there even meant to be a lot of synoptic stuff? Like in Chem 4 i don't remember there being much synoptic stuff at all. Perhaps AQA don't put much in? :s-smilie:
Original post by sd2011
could someone explain how the colorimetry works please?


no need to know it in detail all that it uses light to find concentration of a coloured ion
Reply 368
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empop92
5
jan 11 paper anyone?!?!
Reply 369
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azaking
Original post by jimmy303
How is it wrong?

Just because the beaker with the zinc electrode is on the left doesn't mean it's on the left in the conventional representation. You could just as easily slide the beaker on the table so that it's on the right...



Learning it as RHS-LHS is very risky tbh.

Learn it as:

emf = most positive electrode potential - most negative electrode potential.

In 2b i)

Mg/Mg2+ has a E value of -2.37
Zn/Zn2+ has a value of -0.76

Mg/Mg2+ is most negative
Zn/Zn2+ is most positive

Thus emf = -0.76 - (-2.37)
=1.61V


That's what I use to do, before I came across two questions where the RHS half cell was negative and the LHS was positive. They gave you the conventional representation and to get the correct answer you had to stick to the old EMF= RHS - LHS. So just watch out if they give you the representation :smile:
Original post by InItToWinItGetIt?
But is there even meant to be a lot of synoptic stuff? Like in Chem 4 i don't remember there being much synoptic stuff at all. Perhaps AQA don't put much in? :s-smilie:


Just that all the exams seem to be a bit annoying this exam session haha, so i wouldn't put it past them!
Reply 371
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jimmy303
1
Original post by azaking
That's what I use to do, before I came across two questions where the RHS half cell was negative and the LHS was positive. They gave you the conventional representation and to get the correct answer you had to stick to the old EMF= RHS - LHS. So just watch out if they give you the representation :smile:


Could you show me the questions? :smile:

I've never come across an instance where emf = most positive - most negative doesn't work because emf if a measure of the difference between the two electrode potentials and most positive - most negative works out that difference.
Someone give tips on how to make drawing born-haber cycles easier? Can't seem to get a hang of them.
Can anyone explain how you draw a fuel cell diagram please given two equations?

E.g.

1.) O2 + 2H2O + 4e ---> 4OH-
V= 0.4
2.) 2H2O + 2e ---> 2OH- + H2
V= -0.83
Thanks, what do you do? Take products of both on one side? Or products of one, reactants of another on one side of the representation?

Help pleaseeeeee :smile:
On the January 2011 paper, Question 7. b) ii) it tells you to write an overall equation. But I can't do the balancing for the Cr half equation, I can get the elements to balance but not the charges, and the markscheme just gives you the overall reaction rather than the half equation.

Can anyone help me please?
Reply 375
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ceeebs
Original post by jimmy303


Hydrogen Fuel Cells:

+ Don't need to recharge (short intermediate time between uses)
+ Only waste is water (no CO2 or toxins)

- Energy needed to produce Hydrogen gas which is usually done by electrolysis which uses electricity generated from fossil fuels (so therefore not carbon neutral).
- Hydrogen is flammable so storage and transport is difficult and/or costly.


Do you know what the equations are for electrolysis? actually I dont even know what electrolysis is. dont ask how i got 95% on unit 2 because im sure it was in there somewhere?!
anyway Care to shed light pleeeeeeeeeeeeeease?
Reply 376
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mrppaulo
Original post by empop92
jan 11 paper anyone?!?!


the papers and mark schemes and revision materials are here:
www.a-levelchemistry.co.uk
Reply 377
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ceeebs
Does anybody know what synoptic topics I should look at? I know Chem5 isn't usually toooo synoptic but just incase AQA are feeling extra nasty this year and want to give us a paper like Bio5 urgh.
Was thinking of learning conditions and reagents for reactions eg. unit 2/4 but Im not sure whether it will just be a waste of time lol
Reply 378
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SkyHunter
Hi, can somebody help me with this question please...
Its question 2b in topic 14.3 of the nelson thornes book
the equation given is: I2(aq)+2Br(aq)--->Br2(aq)+2I-
the E value of Br2+2e- -->2Br- =+1.07
the E value of I2+2e- --->2I- =+0.54

I worked the emf out to be 0.53 but the answers at the back say its -0.53 :confused:

help? please? :frown:
When doing deltaG = deltaH - TdeltaS

When should you divide by 1000? I am always confused about that bit.

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