HELP!!! Organic chemistry question??

Original post by QueenC_87

Q1) When bromide ions react with acidified silver nitrate you get a cream precipitate.
Haloalkanes are generally insoluble in water and soluble in organic solvents. Haloalkanes cannot H-bond with water. In non-polar solvents the attraction between the haloalkanes and the solvent is a strong (or stronger) than the attraction of solvent for solvent particles. Hence I think you want a secondary haloalkane ("bromo"alkane).

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Q2) alcohols or carboxylic acids containing C-OH react with PCl5 and misty fumes of HCl are produced.
acidified potassium dichromate will oxidise a primary or secondary alcohol.
You are told it is a primary species, so you want a primary alcohol that is a liquid at room temperature.

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(edited 9 years ago)

Reply 2

Original post by Claree

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You are a star!!! can you help me with two more

1) A liquid that is not soluble in water. It burns to give a yellow flame with very little soot. It does not remove the colour from bromine water- the water stays orange???

2) A liquid that gives a positive 2.4 dinitrophenylhydrazine test- yellow/orange crystals are formed. It reacts with Fehlings solution to give a red solid???

You are a life saver if you can answer just them two. Thank you so much!

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Original post by Claree

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Please

Reply 4

Original post by QueenC_87

Sorry I was at a concert this evening!

1) Non sooty flame means low C :h:

ratio, so it's not an aromatic compound I.e. it's not benzene. Not decolorising bromine water means there are no C=C double bonds. I guess it will be an alkane then (non polar so doesn't dissolve in water) that's a liquid e.g. propane. Propane burns with a yellow flame.

I'm on my phone, will reply to the other q when I get home. :smile:

Reply 5

Original post by Claree

Sorry I was at a concert this evening!

1) Non sooty flame means low C :h:

You are absolutely amazing!!! thank you. The second question gives me a hint that it is a four carbon compound so I have Butanal. Will you let me know when you get a chance if this is correct? Thank you xxx

Reply 6

Gibber96

Original post by QueenC_87

Positive test with 2,4-dinitrophenylhydrazine indicates a C=O from an aldehyde or ketone (not from a COOH group), and reacting with Fehlings means it is oxidised to give a carboxylic acids. Ketones can't be oxidised by Fehling's, so the answer is any aldehyde e.g. ethanal

Reply 7

Original post by Gibber96

The answer should contain four carbon atoms therefore the answer would be Butanal?

Reply 8

Gibber96

Original post by QueenC_87

The answer should contain four carbon atoms therefore the answer would be Butanal?

That's right!

Reply 9

Original post by Gibber96

That's right!

Woo hoo. I'm new to organic chemistry, only just started this module two weeks ago. It's taking time to get my head round it but I am getting there! Thank you both for your help! Much appreciated. xxxxxxx

Reply 10

Original post by QueenC_87

2) The first test shows a C=O in aldehyde or ketone, the second test narrows it down to an aldehyde. As it's a liquid, it could be e.g. ethanal. :smile:

Reply 11

Original post by Claree

2) The first test shows a C=O in aldehyde or ketone, the second test narrows it down to an aldehyde. As it's a liquid, it could be e.g. ethanal. :smile:

Thank you so much! I really appreciate the help you have given me, particularly for giving me an explanation and not just an answer. It helped my understanding. xxxx

Reply 12