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

Original post by AqsaMx

Because the units are in g mol-3 not in mol dm-3 so you have to multiply the concentration by mr to get it to g dm-3.

Omg i get it thank you, just replying made me realise haha, thanks for the help! Hope my explanation helped you too?

Posted from TSR Mobile

Reply 122

Original post by zirak46

Omg i get it thank you, just replying made me realise haha, thanks for the help! Hope my explanation helped you too?

Posted from TSR Mobile

Yes thank you it did. But you know how the second product has a -S-S- bond reformed, how do you know the disulphides bond is made again when it doesn't tell you?

Reply 123

rory58824

2

Just remember guys, questions like that disulfide bond are the most challenging ones. That one was only 2 marks out of 100. If you get a similar situation in the real one just move on and try to score best on the other 98 marks. You're better off getting 5 easy marks on a buffer solution than spending a long time on a 2 mark question.

Reply 124

That all seems right!
Just to make sure, recap of what happens from what I understand:

-conc of NO2 has been increased
-meaning system no longer in equilibrium
-Kc isnt affected and therefore doesnt change
-this is because top of kc expression will increase until the original value of Kc is reached

(edited 7 years ago)

Reply 125

From my understanding:

Kc is conc of products / conc of reactants
Changing temp will change VALUE of Kc
Changing conc or pressure will change CONC of prod or reactants
Meaning Kc is altered
But we know kc never changes when change in pressure and conc
Thats because the prod (bottom of expression) or/and reactants (top of expression) will change till Kc is reached

Hope that makes sense and if im wrong, please someone do correct me!

Reply 126

Original post by rory58824

Just remember guys, questions like that disulfide bond are the most challenging ones. That one was only 2 marks out of 100. If you get a similar situation in the real one just move on and try to score best on the other 98 marks. You're better off getting 5 easy marks on a buffer solution than spending a long time on a 2 mark question.

Thats a very good point, took me good 10 mins to the question and i got no marks xD

Reply 127

Original post by rory58824

Just remember guys, questions like that disulfide bond are the most challenging ones. That one was only 2 marks out of 100. If you get a similar situation in the real one just move on and try to score best on the other 98 marks. You're better off getting 5 easy marks on a buffer solution than spending a long time on a 2 mark question.

Yeah that's true, but I'd still like to understand it :smile:

Reply 128

rory58824

2

Original post by AqsaMx

Yeah that's true, but I'd still like to understand it :smile:

Check this video out, I don't have the time to explain it at the moment but I think this is a pretty good explanation. Go to 33:32 in the video if you want the explanation for that question:

https://www.youtube.com/watch?v=pwrLHwFh4KM

Reply 129

Can someone please help me out with this?
I dont understand enthalpy change of solution and enthalpy change of hydration

Posted from TSR Mobile

1462456574183.jpg37.2KB

Reply 130

Is anyone able to give me tips/advice on the evaluative for the relative strengths of weak acids?

(edited 7 years ago)

Reply 131

Im not sure but isnt sulfuric acid h2SO4 so you would need 2 SO2? im probs wrong

Posted from TSR Mobile

Reply 132

Original post by AqsaMx

Is anyone able to give me tips/advice on the evaluative for the relative strengths of weak acids?

Anyone please?

Reply 133

totabatouta

6

Guys I'm soo scared for chemistry; what's everyone doing at this point? Notes or have you guys started doing past papers; I'm retaking both f321 and f322 aswell Sitting A2 this summer👀😭

Posted from TSR Mobile

Reply 134

totabatouta

6

Original post by AqsaMx

Anyone please?

I don't remember doing it but calculating ph would defo come up make sure you know all the mathy part of it? Maybe go over indicators aswell?

Posted from TSR Mobile

Reply 135

Original post by AqsaMx

Anyone please?

Know about acids, bases, indicators inside out - know ranges of indicators, remember how to work out strong acid, strong base, weak acid. Practise your moles questions, etc, and underline words in question, won't be too difficult, youll know EVERYTHING on the test so dont worry

Reply 136

Original post by totabatouta

I don't remember doing it but calculating ph would defo come up make sure you know all the mathy part of it? Maybe go over indicators aswell?

Posted from TSR Mobile

You know with regards to indicators do you actually need to know colour changes and stuff?

Reply 137

Original post by zirak46

Know about acids, bases, indicators inside out - know ranges of indicators, remember how to work out strong acid, strong base, weak acid. Practise your moles questions, etc, and underline words in question, won't be too difficult, youll know EVERYTHING on the test so dont worry

Thank you so much, I appreciate it :smile:

But you know cos the paper is relative strength of weak acids, could they still ask about bases and strong acids?

Reply 138

med456

Does anyone have the f325 2015 past paper & mark scheme? I really need it for revision!

Reply 139