OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

Reply 2620

Messier31

2

Original post by Serine Soul

Me too, I always lose marks on that section
I'm just hoping my practical mark and F324 will keep up an A* :cry:

Same, those and the low F325 boundaries

Reply 2621

username986184

3

Original post by tcameron

Thank you
but what has it got to do with electrode potentials?

Please explain what you mean.

Reply 2622

rory58824

2

Studying on your own is always the best. You get so much more done imo.

Reply 2623

tcameron

19

Original post by TeachChemistry

Please explain what you mean.

how does the topic on electrode potentials lead into the stuff about fuel cells?

Reply 2624

M.Branson98

2

Does anyone have a link to last year's F325 paper and mark scheme?!

Reply 2625

username986184

3

Original post by tcameron

how does the topic on electrode potentials lead into the stuff about fuel cells?

Because the operation of fuel cells depends on the half reactions and electrode potentials.

e.g. under alkaline conditions

2H2O + 2e <--> H2 + 2OH- E = -0.83V
0.5O2 + H2O + 2e <--> 2OH- E = +0.40V

Since the top reaction is more negative than the bottom one, the top reaction will run from right to left. Overall, hydrogen and oxygen is converted to water and the electrons in those half equations that are being transferred are the current for the cell.

Use values in this table to construct a similar whole cell from two half cells under acidic conditions. You will see that E cell is the same.

https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)

Reply 2626

charnot1997

1

Anyone have any method to remember colour changes?

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Reply 2627

pineneedles

14

Original post by ImNervous

No not really
But I guess it would be because the chloride ions that are part of the complex have formed co - ordinate bonds which are essentially dative covalent bonds and are stronger than ionic bonds. I'm not too sure though. And have you checked the answer on the mrkscheme to make sure its complex B? If not could you please check. Thank you very much
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Ah, that would make sense
Yeah, ive just looked and your answer and reasoning were correct 👍

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Reply 2628

thesmallman

9

What are the colour changes we need to know for this exam??
Would we get asked about the colour of any transition element?- so confused lol

Reply 2629

pineneedles

14

Original post by thesmallman

What are the colour changes we need to know for this exam??
Would we get asked about the colour of any transition element?- so confused lol

I don't think we'd just be asked about any but we definitely need to know the colour changes associated with the precipitation reactioms of Cu2+, Fe2+ and Fe3+, and Co2+
We also need to the coloirs of three ligand substitution reactilns, I need to remind myself which ones.
We need to know that dichromate changes from orange to green too. Ive seen a question that asked about the difficulty of using permanganate in a titration, which required knowledge of its two oxidation states and their respective colours I believe

Reply 2630

lai812matthew

10

Original post by thesmallman

What are the colour changes we need to know for this exam??
Would we get asked about the colour of any transition element?- so confused lol

the book's image for transition metal colours

Reply 2631

itsConnor_

11

I don't know what I'm doing with titration curves. Can someone explain?

e.g. https://gyazo.com/b9b5bf5f7a6fbaf84bbcb3bd78916460

Reply 2632

RetroSpectro

2

Can someone please elaborate on this statement from the Spec:

"explain the changes that take place at eachelectrode in a hydrogen–oxygen fuel cell"

Reply 2633

Serine Soul

18

Original post by RetroSpectro

Can someone please elaborate on this statement from the Spec:

"explain the changes that take place at eachelectrode in a hydrogen–oxygen fuel cell"

I'm guessing it means in terms of standard electrode potential values and equilibrium

(edited 7 years ago)

Reply 2634

RetroSpectro

2

Original post by itsConnor_

I don't know what I'm doing with titration curves. Can someone explain?

e.g. https://gyazo.com/b9b5bf5f7a6fbaf84bbcb3bd78916460

Deduce whether you are starting with an acid or a base

If its a strong acid the pH curve will start from a low pH; a weak acid will have a slightly higher pH start but lower than 7

If its a strong base then the start would be a high pH around 14; a weak base would start at a slightly lower pH but above 7

Identify whats added and where the pH is expected to drop to

Reply 2635

Serine Soul

18

Original post by itsConnor_

I don't know what I'm doing with titration curves. Can someone explain?

e.g. https://gyazo.com/b9b5bf5f7a6fbaf84bbcb3bd78916460

First thing you wanna do is identify what the strong acid, weak acid, strong base and weak base are

Reply 2636

RetroSpectro

2

Original post by Serine Soul

I'm guessing it means in terms of standard electrode potential values and equilibrium

As in the equations of H2 splitting and H2O forming from Oxygen, protons and electrons?

Reply 2637

itsConnor_

11

Original post by RetroSpectro

Deduce whether you are starting with an acid or a base

If its a strong acid the pH curve will start from a low pH; a weak acid will have a slightly higher pH start but lower than 7

If its a strong base then the start would be a high pH around 14; a weak base would start at a slightly lower pH but above 7

Identify whats added and where the pH is expected to drop to

Original post by Serine Soul

First thing you wanna do is identify what the strong acid, weak acid, strong base and weak base are

Ok so when you say "if its a strong acid it will start from a low pH" etc. this is the acid that an alkali is ADDED TO and not an acid that is BEING ADDED to an alkali?

Reply 2638

lolo11

1

Original post by zirak46

Hey guys, hope revision is going well.

Could someone please explaim how to do the following questioms from the June 13 paper?

The part d) question refers to the table attached.

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Hi, not too sure if you still need the help.

So for the question regarding CO2, in order to work out mass you need the number of moles of co2. This can be worked out by dividing the TOTAL energy intake by the enthalpy change of reaction (which is given per mole) and multiplying this by 6 due to the stoichiometry of the equation/reaction. This will give you the number of moles so multiply this by the RFM of co2 (44) to give 3.22*10^17 (g).

Reply 2639

ImNervous

2

Original post by lolo11

Hi, not too sure if you still need the help.

So for the question regarding CO2, in order to work out mass you need the number of moles of co2. This can be worked out by dividing the TOTAL energy intake by the enthalpy change of reaction (which is given per mole) and multiplying this by 6 due to the stoichiometry of the equation/reaction. This will give you the number of moles so multiply this by the RFM of co2 (44) to give 3.22*10^17 (g).

But why does dividing the total energy intake by enthalpy change give you moles of c6h12o6? Thank you

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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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