The Planning Exercise To Identify Some Organic Compounds Containing Oxygen.

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The Planning Exercise To Identify Some Organic Compounds Containing Oxygen

In this practical I will try to identify some unknown organic compounds using chemical tests.  The compounds tested are known to have three carbon atoms, six or eight hydrogen atoms, one or two oxygen atoms, and no atoms of any other elements.  We also need to make sure that the compounds can only be alcohols, carbonyl compounds, carboxylic acids or esters.

        Six different compounds that follow the above criteria are used, and these are propan-1-ol, propan-2-ol, propanal, propanone, propanoic acid, and methyl ethanoate.

An aldehyde, propanal, can be identified by first a positive test with 2,4-dinitrophenylhydrazine, showing it is a carbonyl compound and nothing else, where the solution would turn yellow, then a positive test with Tollen’s Reagent, where a ‘silver mirror’ would be formed, showing that the compound can be oxidise.

A ketone, propanone, can be identified by first a positive test with 2,4-dinitrophenylhydrazine, showing it is a carbonyl compound and nothing else, where the solution would turn yellow, then a negative test with Tollen’s Reagent, where no reaction would occur, showing that the compound cannot be oxidised.

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A carboxylic acid, propanoic acid, can be tested with sodium carbonate, a base, and carbon dioxide would be released, showing that the compound is an acid.  This is a valid proof of a carboxylic acid in this group of compounds, as propanoic acid is the only acid.

A primary alcohol, propan-1-ol, can be identified by first a negative test with 2,4-dinitrophenylhydrazine, showing it is not a carbonyl compound, then a positive test with acidified potassium dichromate, where the solution turns green.  The solution is distilled from the acidified potassium dichromate, and then is tested ...

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