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

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Original post by cr7alwayz
For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?


I think You had to show that G was negative using the free energy equation, making the reaction feasible at 25oC bc just because entropy is positive, doesn't mean it's feasible as enthalpy and temperature also contribute to overall feasibility ☺️
Original post by nimoooooooo
Does anyone remember what happens with chemical shift when agno3 is added?


there are no protons and carbons.
Reply 3682
Original post by Cal 1
That's what I did. No reason why not I don't think!


Cool man.. I think was gonna put the hydroxide but realised it's a blue precipitate hahaha
Original post by Cal 1
Unfortunately no. Correct me if I'm wrong, but the question wanted Cu2+ ions, and Cu(OH)2 is a solid in water(precipitate) so wouldn't work:/


I went for the ol' CuCO3, which is also insoluble but I think it would get the mark no? You want to end up with the Cu(HCOO-), because the carbonate and the acid would definitley react, even if it was solid before
Original post by Cal 1
Unfortunately no. Correct me if I'm wrong, but the question wanted Cu2+ ions, and Cu(OH)2 is a solid in water(precipitate) so wouldn't work:/


so Cu(OH)2 wont react with methanoic acid to form the Cu(HCOO)2 salt?
Original post by Ame12345
I think You had to show that G was negative using the free energy equation, making the reaction feasible at 25oC bc just because entropy is positive, doesn't mean it's feasible as enthalpy and temperature also contribute to overall feasibility ☺️


What was the enthalpy? Can you remember?
Reply 3686
It is lattice enthalphy isn't it?
Original post by MrZebraCookie
For the entropy question, I think I used the lattice enthalpy as delta H. How many marks would this lose?
Original post by Cal 1
Unfortunately no. Correct me if I'm wrong, but the question wanted Cu2+ ions, and Cu(OH)2 is a solid in water(precipitate) so wouldn't work:/


:s-smilie:
Reply 3688
Original post by smileez_101
so Cu(OH)2 wont react with methanoic acid to form the Cu(HCOO)2 salt?


CuCO3
2Marks definitions
1Mark reacting 1 and 2
1 Mark for reason
1Mark reacting 6 and 7
1 Mark saying why

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Original post by Z1228
It is lattice enthalphy isn't it?


no dH solution
Reply 3691
Original post by smileez_101
so Cu(OH)2 wont react with methanoic acid to form the Cu(HCOO)2 salt?


Well it's a weak acid reacting with a precipitate that's formed by a reaction with an acid, so I don't think so. I might be totally wrong btw just letting you know cause I almost wrote that too!
Original post by Z1228
It is lattice enthalphy isn't it?


Oh, did you get detla G as -1700ish?
Is this the full answer? I don't get it 🤔
Original post by lai812matthew
there are no protons and carbons.
Original post by HFancy1997
2Marks definitions
1Mark reacting 1 and 2
1 Mark for reason
1Mark reacting 6 and 7
1 Mark saying why

Posted from TSR Mobile


how many marks will i lost if i mistaken write 5 and 6 instead of 6 and 7. but i write a correct equation and explanation at the end.....
Original post by smileez_101
so Cu(OH)2 wont react with methanoic acid to form the Cu(HCOO)2 salt?


An acid can react with a solid to produce the salt. I think it's fine. They've confused parts of the question.
Reply 3696
Damn, for the buffer solution i got the PH of 6.5 but i rounded it up to 7 and i stated it was neutral.

And for Cr acting both oxidising and reducing agent, i assumed that it was asking for Cr in general and not Cr3+ and that they have to happen simultaneously so i did 4 and 6 i think? The two reactions that have Cr in them since one of those reaction goes oxidation way and the other go towards the reducing way.
acid can react with insoluble base.
Original post by Cal 1
Well it's a weak acid reacting with a precipitate that's formed by a reaction with an acid, so I don't think so. I might be totally wrong btw just letting you know cause I almost wrote that too!


if that is true then the exam board made a damn good trick :frown:
Reply 3699
Original post by lai812matthew
acid can react with insoluble base.


But that was a solid that was already formed by a reaction with an acid, most likely a strong one. Why would it suddenly react with methanoic acid?

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