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OCR B (Salters) F332 Tuesday 4th June 2013 Exam Discussion (Now Closed)

Depletion of Ozone
Cl• + O3 ---> ClO• + O2
ClO• + O3 ---> Cl• + 2O2
Overall:O+ O3 --> 2O2
or
Cl• + O3 ---> ClO• + O2
ClO• + O ---> Cl• + O2
Overall: 2O3 ---> 3O2

Which one is right? I thought it would be the top one?
Also how do you work out the overall reaction?

ALSO do we need to know about Ziegler Natta catalysts?

You've mixed up the overall reactions for them, otherwise they are both correct.
To work out the overall reaction, just cancel what you see on both sides e.g. they both have Cl and ClO, so they would cancel, leaving O3 + O ------> 2O2 which would be the overall reaction.

Edit: Just realised you were asking about the depletion of ozone.
It would be this:
Cl• + O3 ---> ClO• + O2
ClO• + O3 ---> Cl• + 2O2
Overall: 2O3 ---> 3O2

(edited 10 years ago)

Reply 381

abzy1234

14

Original post by King Hotpie

January 2011 paper, question 3e)- Surely potassium is a bigger atom than chlorine? According to the mark scheme chlorine is bigger???

It's a given rule that the bigger circle is always the negatively charged ion. You won't be asked to explain this as it's unit 5 stuff, but just take it for granted now that the smaller ones are always the cations :smile:

Reply 382

Jlane5000

4

Original post by Jlane5000

Could some kind person please explain the mark scheme for June 2011, question 4 (d) (i) to me? In the question it asks how to turn methanol into chloromethane. I thought that to turn an alcohol into a chloroalkane that you shake with conc HCl at room temp. However the mark scheme says it is HCl and heat/high temp. I really don't understand where they got that from :confused:

Anyone? I've emailed my teacher about it but he never replied :frown:

Reply 383

super121

5

Original post by Jlane5000

Anyone? I've emailed my teacher about it but he never replied :frown:

Was literally just doing this paper and thought the same thing.

Reply 384

abzy1234

14

Original post by Jlane5000

Anyone? I've emailed my teacher about it but he never replied :frown:

Nucelophilic substitution reactions are usually quite slow, especially when forming halogenoalkanes from alcohols. Thus, high temperature and pressure increases the rate of reaction.

Think of it the context of industry. If we were to use room temperature, industrial processes will be incredibly slow and thus not economically viable. High temperatures and pressures, allows the reaction to speed up; boosting industrial efficiency.

Hope that clears it up! :smile:

Reply 385

krisshP

14

Original post by AGKhan

Thanks yeah I didn't know about that until you mentioned it earlier :smile:

I was just wondering how you would describe the bond angle in an exam sort of thing

Posted from TSR Mobile

I said it before. Look at post 370
http://www.thestudentroom.co.uk/showthread.php?t=2310133&page=19&page=19

Reply 386

Jlane5000

4

Original post by abzy1234

Nucelophilic substitution reactions are usually quite slow, especially when forming halogenoalkanes from alcohols. Thus, high temperature and pressure increases the rate of reaction.

Think of it the context of industry. If we were to use room temperature, industrial processes will be incredibly slow and thus not economically viable. High temperatures and pressures, allows the reaction to speed up; boosting industrial efficiency.

Hope that clears it up! :smile:

It makes sense thanks :smile:

but how do you know when to put that its conc HCl at room temp or HCl under high temp? The question mentioned nothing about it being a specific industrial question, it just said 'methanol can be converted into chloromethane, give the reagent and condition required". There is also no mention of HCl and high temp for this reaction anywhere in the chemical ideas or CGP book, only conc HCl and room temp, which is what most people would think to put for this question :confused:

Could it be an error in the mark scheme?

Reply 387

krisshP

14

Original post by abzy1234

It's a given rule that the bigger circle is always the negatively charged ion. You won't be asked to explain this as it's unit 5 stuff, but just take it for granted now that the smaller ones are always the cations :smile:

Is it because when a negatively charged ion forms, it gains an electron. So say if a set amount of attraction is exerted by the nucleus on all electron, more electrons in total mean less attracted exerted by nucleus on each electron. Hence electrons are more 'out' of the atom, causing a larger atomic radius. Is this right? Haven't gone into A2 yet and won't :smile:

(edited 10 years ago)

Reply 388

booooomblastruin

Original post by pinpin95

what does burn under reflux mean?

The process used to boil volatile substances (such as alcohols) without the loss of reactants or products.

Shown in detail on page 367 of Chemical Ideas

Reply 389

abzy1234

14

Original post by Jlane5000

It makes sense thanks :smile:

but how do you know when to put that its conc HCl at room temp or HCl under high temp? The question mentioned nothing about it being a specific industrial question, it just said 'methanol can be converted into chloromethane, give the reagent and condition required". There is also no mention of HCl and high temp for this reaction anywhere in the chemical ideas or CGP book, only conc HCl and room temp, which is what most people would think to put for this question :confused:

Could it be an error in the mark scheme?

Always put concentrated HCL with high temperature/pressure. Sadly, OCR likes to be specific, so whilst there is nothing wrong with room temperature as a condition- indeed as you said many books quote that- they seemingly prefer the condition of high temperatures/pressures. Legacy papers have also used that condition. Mark schemes are never inaccurate; it's a collective document that's done by several examiners :tongue:

Original post by krisshP

Is it because when a negatively charged ion forms, it gains an electron. So say if a set amount of attraction is exerted by the nucleus on all electron, more electrons in total mean less attracted exerted by nucleus on each electron. Hence electrons are more 'out' of the atom, causing a larger atomic radius. Is this right? Haven't gone into A2 yet and won't :smile:

Slightly right, it's more to do with charge density, which you really don't need to worry about now. It's good that you have a general idea about it now :smile:

Reply 390

Jlane5000

4

Original post by abzy1234

Always put concentrated HCL with high temperature/pressure. Sadly, OCR likes to be specific, so whilst there is nothing wrong with room temperature as a condition- indeed as you said many books quote that- they seemingly prefer the condition of high temperatures/pressures. Legacy papers have also used that condition. Mark schemes are never inaccurate; it's a collective document that's done by several examiners :tongue:

Slightly right, it's more to do with charge density, which you really don't need to worry about now. It's good that you have a general idea about it now :smile:

Okay thanks for all your help :biggrin:

Reply 391

krisshP

14

As an estimate for the average F332 how many marks out of the 100 are needed for an A
Thanks

Reply 392

Welbeck

3

Yeah, on the whole it varies, has been as low as 60 before but as high as 80 (jan 12) and jan 13 was 72 (all for achieving an A). But your right, over the past few years the boundaries have risen.

Reply 393

krisshP

14

reagents and conditions742]I remember last year the grade boundaries shot quite significantly. I can't remember what they were though but it wasn't nice :frown:

How many marks out of 100 is it usually for an A?