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

1. (Original post by Willszz1)
(u) describe in outline the preparation of a chloroalkane from
an alcohol using HCl:

What is this specifically asking for? It's probably something simple but I've never seen something that asks for the preparation of chloroalkane etc

Is it just like ch3cl+ h20 -> ch3oh+ hcl? Or something else
i believe it is asking for the technique if its 3 marks or more so how you shake it with sodium hydrogen carbonate to remove acidic impurities then run off the chloroalkane layer and add anhydrous sodium sulfate to remove water then it is purified by distillation
2. (Original post by Welbeck)
Do you need to remember planck's constant?
Nope
3. 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?
4. (Original post by krisshP)
Dunno what dative bond you are on about.

Around central O atom there are 3 areas of electron density which repel one another s far apart as possible. Hence ozone has a V shape with a bond angle 118.5*.

120-2.5*=118.5* due to 1 lone pair squeezing bond angle by 2.5* per lone pair.

It has a dative bond and a double bond but I think the pi bond from the double is shared. I tried reading up on it online and many places say the bond angle is 116.8° (116.78°)
5. (Original post by AGKhan)

It has a dative bond and a double bond but I think the pi bond from the double is shared. I tried reading up on it online and many places say the bond angle is 116.8° (116.78°)
It does NOT matter what bond it is. The main thing is it being an AREA of electron density.
6. (Original post by krisshP)
It does NOT matter what bond it is. The main thing is it being an AREA of electron density.
Thanks yeah I didn't know about that until you mentioned it earlier I was just wondering how you would describe the bond angle in an exam sort of thing

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7. 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?
8. January 2011 paper, question 3e)- Surely potassium is a bigger atom than chlorine? According to the mark scheme chlorine is bigger???
9. (Original post by Welbeck)
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.

It would be this:
Cl• + O3 ---> ClO• + O2
ClO• + O3 ---> Cl• + 2O2
Overall: 2O3 ---> 3O2
10. (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
11. (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
Anyone? I've emailed my teacher about it but he never replied
12. (Original post by Jlane5000)
Anyone? I've emailed my teacher about it but he never replied
Was literally just doing this paper and thought the same thing.
13. (Original post by Jlane5000)
Anyone? I've emailed my teacher about it but he never replied
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!
14. (Original post by AGKhan)
Thanks yeah I didn't know about that until you mentioned it earlier I was just wondering how you would describe the bond angle in an exam sort of thing

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I said it before. Look at post 370
http://www.thestudentroom.co.uk/show...age=19&page=19
15. (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!
It makes sense thanks 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 Could it be an error in the mark scheme?
16. (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
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
17. (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
18. (Original post by Jlane5000)
It makes sense thanks 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 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

(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
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
19. (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

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
Okay thanks for all your help
20. As an estimate for the average F332 how many marks out of the 100 are needed for an A
Thanks

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