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OCR Gateway Chemistry C4C5C6 - 13/06/13

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Reply 340

L'Evil Fish

Original post by andersson

Haha, I mean like perfected! Not just skimmed over :tongue:

30 minutes then.

Reply 341

Red Fox

Original post by andersson

Haha, I mean like perfected! Not just skimmed over :tongue:

Do you mean taking notes or doing questions or what? I would have though you could revise the whole course in that time.

Reply 342

Puffin111

Please please please can someone explain to me the section on chlorine radicals!!

Reply 343

L'Evil Fish

Original post by Puffin111

Please please please can someone explain to me the section on chlorine radicals!!

UV breaks CCl(2)Fl(2) into CClFl(2) and Cl ¤

Cl¤ + O(3) ---> ClO¤ + O(2)
ClO¤ + O(3) ---> 2O(2) + Cl¤

And it keeps breaking it yp

Reply 344

NatashaG

Original post by L'Evil Fish

UV breaks CCl(2)Fl(2) into CClFl(2) and Cl ¤

Cl¤ + O(3) ---> ClO¤ + O(2)
ClO¤ + O(3) ---> 2O(2) + Cl¤

And it keeps breaking it yp

My book is different it says

Cl¤ + O(3) ---> ClO¤ + O(2)

ClO¤ + O¤ ---> Cl¤ + O(2)

I assume both are correct? but wanted to check that one isn't definitely wrong

Reply 345

NatashaG

Original post by BP_Tranquility

True, but nobody's actually say the specimen exam and its initial purpose was to provide schools with an idea on how the exam would be set out...in our exam, they probably will take into account the different answers (although my chemistry teacher emailed OCR regarding this and they said it doesn't matter apparently)... :wink:

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Oh right thanks :P grrr OCR's specimens always annoy me > :frown:

unluckily all my A-levels are going to be OCR....

Reply 346

ryanb97

Original post by NatashaG

My book is different it says

Cl¤ + O(3) ---> ClO¤ + O(2)

ClO¤ + O¤ ---> Cl¤ + O(2)

I assume both are correct? but wanted to check that one isn't definitely wrong

either one is correct since the chlorine radical is left at the end of each reaction...so the chain reaction continues

Ryan

Reply 347

Red Fox

Original post by NatashaG

My book is different it says

Cl¤ + O(3) ---> ClO¤ + O(2)

ClO¤ + O¤ ---> Cl¤ + O(2)

I assume both are correct? but wanted to check that one isn't definitely wrong

I'd go with L'Evil's because the chlorine oxide is more likely to react with ozone than an oxygen radical because the stratosphere is full of ozone.

Reply 348

Puffin111

Thanks! So if that was to come up as a 6 marker what kind of stuff would you be expected to write?

Reply 349

vi0laa

I've just done the specimen and I noticed that quite a few questions were taken from the old specification past papers..

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Reply 350

carns

Does anyone know previous grade boundaries for C4,C5,C6 exam, because I cannot find them for previous years only for C1,C2,C3 ?

Reply 351

Puffin111

Original post by carns

Does anyone know previous grade boundaries for C4,C5,C6 exam, because I cannot find them for previous years only for C1,C2,C3 ?

I think that's because this is the first year of the new specification to do the C4 C5 C6 exam

Reply 352

Mathangi

How do we know which is the endothermic/exothermic direction of an equilibrium reaction?

Or does it just tell you?

Reply 353

Red Fox

Original post by cameron262

How do we know which is the endothermic/exothermic direction of an equilibrium reaction?

Or does it just tell you?

It tells you. Have a look at the 6 marker for C5 in the specimen paper.

Reply 354

BP_Tranquility

Original post by cameron262

How do we know which is the endothermic/exothermic direction of an equilibrium reaction?

Or does it just tell you?

Exothermic is a bond making process.
Endothermic is bond breaking process.

2SO₂ +O₂ ->2SO₃

The arrow is supposed to be reversible, so it's an equilibrium mixture. :smile:

The arrow that goes to the right is exothermic (since bonds are created as SO₂ and O₂ react, "joining" up these molecules to give SO₃).

The arrow that would go to the left is endothermic (as the bonds in sulfur trioxide are broken, "splitting" the SO₃ molecule to give back SO₂ and SO₃).

Hope this helps :biggrin:

Reply 355

Elcor

Original post by Red Fox

Do you mean taking notes or doing questions or what? I would have though you could revise the whole course in that time.

I mean doing the CGP question booklet too, I'm a third through it now.

Reply 356

dazzer19

If a six mark question came up on Chlorine radicals, there isn't exactly 6 things to write? There are literally 3 / 2 stages and 1 mark for good english = 4 marks tops :/

Reply 357

BP_Tranquility

Original post by dazzer19

If a six mark question came up on Chlorine radicals, there isn't exactly 6 things to write? There are literally 3 / 2 stages and 1 mark for good english = 4 marks tops :/

You could talk about why CFCs were used in the first place, they take a long time to break down, write down the equations, how to ozone protects us from UV rays, and replacements (e.g. HFCs)... :tongue:

Reply 358

carns

Original post by dazzer19

If a six mark question came up on Chlorine radicals, there isn't exactly 6 things to write? There are literally 3 / 2 stages and 1 mark for good english = 4 marks tops :/

6 mark question are not about writing 6 things, if u look at mark schemes it tells stuff like full understanding, or writing an equation and discussing other things. Its about showing a detailed scientific overview of the topic. +decent spelling ect