Really need some help with unit 2 AS Chemistry!

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natc26
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On the unit 2 past paper from June 2015, question 2 is about test tube tests to distinguish between compounds. Each question asks for the reagent required for the test and observations for both compounds.

2 (a) is butan-2-ol and 2-methylpropan-2-ol
2 (b) is propane and propene

I cant seem to find anything about this in any of the text books and revision resources I have looked at.

Any help would be much appreciated, thanks!
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ahsan_ijaz
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Hi,

You have br2 confused - you meant to say it turns orange to colourless when it's unsaturated
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Sunethra
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(Original post by natc26)
On the unit 2 past paper from June 2015, question 2 is about test tube tests to distinguish between compounds. Each question asks for the reagent required for the test and observations for both compounds.

2 (a) is butan-2-ol and 2-methylpropan-2-ol
2 (b) is propane and propene

I cant seem to find anything about this in any of the text books and revision resources I have looked at.

Any help would be much appreciated, thanks!
Have you not learnt about oxidation? Well, if not you need to read chemiguide or any other chemistry resource!

2(a) Butan-2-ol is a secondary alcohol while 2-methylpropan-2-ol is a tertiary alcohol. You can use acidified potassium dichromate (vi) and then you'd realize that the butan-2-ol solution turns form orange to green while the 2-methylpropan-2ol solution doesn't change in colour because it doesn't have H to be oxidized to form water.

2(b) This is simply unit 1. you can test for double bonds using bromine water or acidified potassium manganite. Bromine water truns from orange to colourless in alkene and remains the same for alkane. Pottasium Mangante changes from purple to colourless with an alkene.
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natc26
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(Original post by RasputinReborn)
If you cannot find these in your textbooks, then it's vital you buy new ones (they should be exam board specific too). Anyways.

The first question shows you a secondary alcohol and a tertiary alcohol. We know that tertiary alcohols cannot be oxidised where as secondary alcohols can be oxidised. Therefore, the reagent you use is acidified potassium dichromate(VI) (an oxidising agent)which will change from orange to green when added to butan-2-ol, but they'll be no colour change when added to 2-methylpropan-2-ol.

The next question shows an alkane and an alkene. To distinguish between saturated and unsaturated compounds, you add bromine water. It will remain brown when added to propane as it's an alkane(saturated compound), however, when it's added to propane, bromine water will change from brown to colourless, since propene is unsaturated.
(Original post by Sunethra)
Have you not learnt about oxidation? Well, if not you need to read chemiguide or any other chemistry resource!

2(a) Butan-2-ol is a secondary alcohol while 2-methylpropan-2-ol is a tertiary alcohol. You can use acidified potassium dichromate (vi) and then you'd realize that the butan-2-ol solution turns form orange to green while the 2-methylpropan-2ol solution doesn't change in colour because it doesn't have H to be oxidized to form water.

2(b) This is simply unit 1. you can test for double bonds using bromine water or acidified potassium manganite. Bromine water truns from orange to colourless in alkene and remains the same for alkane. Pottasium Mangante changes from purple to colourless with an alkene.
Thanks for the help guys it is really appreciated. I have the official AS Chemistry text book by aqa and a CGP revision guide and I can't find anything which would help me with this but hopefully I am just missing it and it's in there somewhere. I appreciate the explanation behind the answers as well!

Thanks for the heads up about chemiguide Sunethra and I have learned about oxidation but evidently not in great detail :/
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