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# Edexcel 6CH07/01- May 8th 2013 - AS Chemistry Unit 3B watch

1. (Original post by NilFBosh)
BTW. That paper that we did in CLASSSSSSS today. The first MCQ. Was it D?
It was C.
D was protective layer ( of indicator)
But iodine has starch surrounding and protecting it....so how can end point be accurate?
2. (Original post by Relaxedexams)
(1) The OH- ion hydrolyses the C-halogen bond BEFORE the acid is added.

(2) Then acid is added to remove excess OH- ions.

(3) Then aqueous AgNO3 is added to obtain a silver halide ppt.

If OH- ions were not removed in step (2), in step (3) Silver oxide ppt will form.
Ohhhh! I got it! Thanks!!!!

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3. When drawing the reflux condenser, we should show an electric heater or a water bath? (If the question does not specify how it was heated), or is it ok to just draw an arrow labelled 'Heat'?
4. Relaxedexams I wud say that better show water bath/electric heater
5. Anyone please explain how to do these questions (if you can explain in detail please do)

http://www.flickr.com/photos/9550785...n/photostream/

http://www.flickr.com/photos/9550785...n/photostream/
Attached Images

6. (Original post by Gunner121)
Anyone please explain how to do these questions (if you can explain in detail please do)

http://www.flickr.com/photos/9550785...n/photostream/

http://www.flickr.com/photos/9550785...n/photostream/
The first question asks for you to work out the RMM of the isomers.

From part a(i) you know that the precipitate should be AgI from the yellow colour. This means that your formula has to have an Iodide which is mass 126.9
If the RMM is 169.9', you can do subtraction 169.9-126.9= 43
From 43, you can work out the rest of the formula to be C3H7

So, the formula is C3H7I

As for the second question.... I remember that question, in class we asked our teacher about it, he said it was out of the specification... So no need to worry about it.

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7. (Original post by Gunner121)
Anyone please explain how to do these questions (if you can explain in detail please do)

http://www.flickr.com/photos/9550785...n/photostream/

http://www.flickr.com/photos/9550785...n/photostream/
2 (a)

Liquid B forms a red ppt, so it must be an aldehyde and alcohol X is a primary alcohol.

Molar mass = 60
Molar mass of carbon chain (without OH group) = 60-17=43
Molar mass 43= C3H7
So molecular formula of Alcohol X and Y= C3H7OH

Displayed formula of liquid B = C-C-C=0 (fill the remaining H bonds)

Name of alcohol X - Propan-1-ol

2 (a) (!!)

Molar mass of carbon chain = 169.9 - Iodine molar mass
=169.9-126.9
=43

So molecular formula of carbon chain - C3H7
Molecular formula - C3H7I
8. (Original post by leafy9)
As for the second question.... I remember that question, in class we asked our teacher about it, he said it was out of the specification... So no need to worry about it.

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If the previous question was in the specification, how can this be not in the specification? They are identical. Besides that was a past paper question, Edexcel will never give an out of spec question.
9. Hey gunner 121 this is the answer to your first question

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10. (Original post by Relaxedexams)
If the previous question was in the specification, how can this be not in the specification? They are identical. Besides that was a past paper question, Edexcel will never give an out of spec question.
To be honest, what he said was that because it was a Jan 2010 paper, it was one of the last papers using the old spec. Since the 'testing for ions' question of that paper wasn't in the table format like many of the other papers.

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11. (Original post by leafy9)
To be honest, what he said was that because it was a Jan 2010 paper, it was one of the last papers using the old spec. Since the 'testing for ions' question of that paper wasn't in the table format like many of the other papers.

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May 2012 or Jan 2012 paper. In one of them, the 'testing for ions' question wasn't in table form too, so its not a must to be in table form for the new spec.
12. (Original post by Relaxedexams)
May 2012 or Jan 2012 paper. In one of them, the 'testing for ions' question wasn't in table form too, so its not a must to be in table form for the new spec.
Then again, January 2013 has the table format.
Btw, just say it was in the spec, how would you answer that question? (Entire qu2 of Jan 2010) We didn't learn anything about that in school.

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13. (Original post by leafy9)
Then again, January 2013 has the table format.
Btw, just say it was in the spec, how would you answer that question? (Entire qu2 of Jan 2010) We didn't learn anything about that in school.

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2 (a)

Liquid B forms a red ppt, so it must be an aldehyde and alcohol X is a primary alcohol.

Molar mass = 60
Molar mass of carbon chain (without OH group) = 60-17=43
Molar mass 43= C3H7
So molecular formula of Alcohol X and Y= C3H7OH

Displayed formula of liquid B = C-C-C=0 (fill the remaining H bonds)

Name of alcohol X - Propan-1-ol
14. Any one pleaaase explain to me question 1 a(iv) in jun 2009
15. (Original post by leafy9)
Then again, January 2013 has the table format.
Btw, just say it was in the spec, how would you answer that question? (Entire qu2 of Jan 2010) We didn't learn anything about that in school.

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Yes its not in the AS specs but in Unit 5 it comes into action.
The two isomers are a ketone and an aldehyde. The aldehyde reacts because it can be further oxidised but not the ketone. I don't know, the question was a horrible heart attack for those who did the paper, even though the examiner's report was positive about this question.
We should learn it anyway. Test to distinguish between an aldehyde and ketone typically isomers.

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16. (Original post by StUdEnTIGCSE)
Yes its not in the AS specs but in Unit 5 it comes into action.
The two isomers are a ketone and an aldehyde. The aldehyde reacts because it can be further oxidised but not the ketone. I don't know, the question was a horrible heart attack for those who did the paper, even though the examiner's report was positive about this question.
We should learn it anyway. Test to distinguish between an aldehyde and ketone typically isomers.

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Test to distinguish between ketones and aldehydes is in our spec!

Fehling's/Benedict's or Tollen's reagent.
17. How to investigate the solubility of simple molecules in different solvents?

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18. (Original post by Relaxedexams)
Test to distinguish between ketones and aldehydes is in our spec!

Fehling's/Benedict's or Tollen's reagent.
Yes its there BUT NOT with Tollens or fehlings reagents. This might be an accepted alternative.
But
You could distinguish by a refluxing with acidified Potassium Di Chromate (or manganate if you take necessary precautions). Colourchange will only show up for aldehyde.
Tollens solution or fehling is also good but out of the spec.

Similarly distinguishing between carboxylic and aldehyde or ketone can be done by litmus.

I dont know. where in the spec is Tollens reagent and Fehling's mentioned????
19. pleeeeassse help me in Jun 2009 q 1 (aiv) and b(v)....didnt get AT ALL!!! http://www.edexcel.com/migrationdocu...e_20090515.pdf
20. (Original post by StUdEnTIGCSE)
Yes its not in the AS specs but in Unit 5 it comes into action.
The two isomers are a ketone and an aldehyde. The aldehyde reacts because it can be further oxidised but not the ketone. I don't know, the question was a horrible heart attack for those who did the paper, even though the examiner's report was positive about this question.
We should learn it anyway. Test to distinguish between an aldehyde and ketone typically isomers.

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Never like it when edexcel does that... This Jan, for biology unit 1 there was a question which I had no clue about, after exam we (year 12s) asked around and found out the question came from A2 from the year 13s biology textbook.......

Thanks by the way. Makes sense.

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