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

okay guys so on the spec it says
use a radical mechanism as a model to explain the reaction of alkanes with halogens (a radical chain reaction in the presence of UV radiation to form halogenoalkanes)
I;m not entirely sure if this is what you were asking for but here you go:

http://www.chem.ucalgary.ca/courses/...h04/ch4-7.html
it's a bit like when you have to calculate empirical formula, only on this question you're given fractions. just do (1/3) divided by Mr of KCl and (2/3) divide by Mr of NaCl and then divide both answers by the smallest one and you should get 1 and something else.
feel free to ask me for a better explanation if you still don't understand
Heyy thanks for the reply, I kind of get it but I can't work methodically unless I know where the method is coming from, if you know what I mean?

Why is it that its a 1/3 or 2/3 divided by Mr?
Why is it that after the first division you divide it by the smallest number?

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3. (Original post by Branny101)
Heyy thanks for the reply, I kind of get it but I can't work methodically unless I know where the method is coming from, if you know what I mean?

Why is it that its a 1/3 or 2/3 divided by Mr?
Why is it that after the first division you divide it by the smallest number?

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Ok so basically you know that out of a total of 3, 2 units of the mass is NaCl and 1 unit is KCl. Now you are asked to find the mole ratio. Using n=m/Mr, you find the moles of NaCl = 2/58.5 and the moles of KCl = 1/74.6.
Now as for the ratio if you had 4 dogs and 8 cats, you would divide by the smallest to get the simplest ratio. i.e the ratio of dogs: cats is 1:2 (excuse my weird example lol ) so you do the same to find the ratio of moles. Does that help explain the method ?
Ok so basically you know that out of a total of 3, 2 units of the mass is NaCl and 1 unit is KCl. Now you are asked to find the mole ratio. Using n=m/Mr, you find the moles of NaCl = 2/58.5 and the moles of KCl = 1/74.6.
Now as for the ratio if you had 4 dogs and 8 cats, you would divide by the smallest to get the simplest ratio. i.e the ratio of dogs: cats is 1:2 (excuse my weird example lol ) so you do the same to find the ratio of moles. Does that help explain the method ?
Thanks! I think I geddit now
5. This document may be useful as it explains some of the reactions (I am aware that some of it is irrelevant to F332)
Attached Files
6. Aliphatic Organic Synthesis 1.doc (390.5 KB, 7479 views)
7. sorry if this has already been mentioned or posted on another thread, but does anyone have a list of all the specific reactions and conditions that are needed?
8. (Original post by ashxx)
sorry if this has already been mentioned or posted on another thread, but does anyone have a list of all the specific reactions and conditions that are needed?
I've posted it either in this thread or the one for the pre-release
9. Heres some more model answers:

Making a halogenoalkane from an alcohol
- Shake methylpropan-2-ol with conc. HCl (keep releasing the pressure)
- Allow the mixture to settle and run off the lower aqueous layer, leaving the impure halogenoalkane
- Neutralise the excess acid by adding sodium hydrogen carbonate solution and run the lower layer off
- Add distilled water and run off the lower layer (this gets rid of any remaining inorganic impurities)
- Remove any remaining water by adding anhydrous sodium sulfate (a drying agent)
- Remove remaining organic impurities by distilling the mixture

The greenhouse effect
- The sun emits energy, in the form of UV light, onto the Earth
- The Earth absorbs this energy and re-emits IR
- CO2, in the troposphere, absorbs some IR in the 'IR window'
- making the bonds vibrate more
- this turns into kinetic energy, raising the temp.
- some O2 molecules radiate IR which warms the Earth
- more CO2 means more radiation and hence a warmer Earth

What happens to the temperature in the atmosphere as you move away from the Earths surface to the top of the stratosphere?
- the temperature decreases in the troposphere and you move away from the Earth
- because hot gases near the Earths surface rise and cool
- within the stratosphere
- the temperature of the atmosphere rises as you move away from the Earth
- due to exothermic reactions

How do we know that halogenoalkanes deplete ozone?
- They break down in the presence of UV light to form radicals
- the radicals catalyse the breakdown
- low concentrations of ozone were found above the antarctic

Why do reactions between atoms occur more quickly at the top of the troposphere?
- conc of gases is higher at the top of the troposphere
- so more collisions occur between the molecules per second
10. (Original post by super121)
I've posted it either in this thread or the one for the pre-release
ahh yes i've found it just gunna post the thread link here just in case anyone else wants it, save them from combing through the pages

http://www.thestudentroom.co.uk/show...&page=2&page=2
11. Heyy Guys does anyone have the Jan. 2013 paper and mark scheme available?

Would help alot; thaanks!
12. (Original post by Branny101)
Heyy Guys does anyone have the Jan. 2013 paper and mark scheme available?

Would help alot; thaanks!
I've put the mark scheme up, but you'll have to find the paper somewhere else

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13. Hmmm thanks - where abouts is it?

And I need the paper more than anything

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14. (Original post by Branny101)
Hmmm thanks - where abouts is it?

And I need the paper more than anything

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Somewhere on this thread or the pre-release one. I'll try and get hold of the paper

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15. (Original post by Branny101)
Hmmm thanks - where abouts is it?

And I need the paper more than anything

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here!
Attached Images
16. 2013_F332_January (1).pdf (236.3 KB, 85 views)
17. 2013_Markscheme_January_F332.pdf (193.2 KB, 91 views)
18. 2013_F332_January_advance_notice.pdf (229.2 KB, 48 views)
19. (Original post by nukethemaly)
here!
THANKS MATE

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20. (Original post by nukethemaly)
here!
Thanks a lot!
21. Heyy could someone explain Jan. 2013, Q 4 c i) I don't understand why the mark scheme has drawn the isomer like that, isn't it just the methyl group that swaps?

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22. (Original post by Branny101)
Heyy could someone explain Jan. 2013, Q 4 c i) I don't understand why the mark scheme has drawn the isomer like that, isn't it just the methyl group that swaps?

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It's the C=O on the C=C on the left that 'swaps' so it on the other side of the carbon double bond.

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23. (Original post by super121)
It's the C=O on the C=C on the left that 'swaps' so it on the other side of the carbon double bond.

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Omg thanks but how would you know to swap that as apposed to the methyl groups?

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24. (Original post by Branny101)
Omg thanks but how would you know to swap that as apposed to the methyl groups?

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The molecule has E/Z isomers because of the carbon double bond on the right. It can't be the one on the left because there isn't 2 different groups on each carbon of the carbon double bond. You can swap the methyl groups because they are bonded to different carbon double bonds.
It may help to draw out the full structural formula to understand it better.

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