The Planning Exercise To Identify Some Organic Compounds Containing Oxygen Essays

The Planning Exercise To Identify Some Organic Compounds Containing Oxygen Essays The Planning Exercise To Identify Some Organic Compounds Containing Oxygen Essay The Planning Exercise To Identify Some Organic Compounds Containing Oxygen Essay 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 Tollens 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 Tollens Reagent, where no reaction would occur, showing that the compound cannot be oxidised. 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 positively with universal indicator paper, which turns red, showing the presence of acid. A secondary alcohol, propan-2-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 negatively with universal indicator paper, which dont change colour, showing the absence of acid, and thus can only be a ketone, meaning the original compound is a secondary alcohol. An ester, methyl ethanoate, can be identified by first a negative test with 2,4-dinitrophenylhydrazine, showing it is not a carbonyl compound, then a negative test with acidified potassium dichromate, where the solution do not change colour, showing it can not be oxidised, as it can only be propanoic acid or methyl ethanoate, then a negative test with sodium carbonate in which no gas is produced, shows that it is methyl ethanoate. Apparatus 1 test tube rack, 7 test tubes, 1 pipette, 1 distilling column, 1 beaker, 1 small conical flask, 1 Bunsen burner, 6 unknown organic solutions, 1 safety spectacles, 1 heat proof mat, 1 gauze, 1 tripod, solution of 2,4-dinitrophenylhydrazine, universal indicator paper, solution of Tollens Reagent, solution of acidified potassium dichromate, solution of sodium carbonate. Method Do the following sequence of tests for all the unknown solutions: -Add 1cm3 of the unknown solution into a test tube, add 3 drops of 2,4-dinitrophenylhydrazine solution, heat in boiling water bath, record the colour change. -Add 1cm3 of the unknown solution into a test tube, add 3 drops of Tollens Reagent, warm in hot water bath, observe the presence of silver mirror. -Add 20cm3 of the unknown solution into a small conical flask, add 1cm3 of acidified potassium dichromate into the solution, heat the solution for 5 minutes and observe the colour change. Distill the solution in the conical flask, and test the distilled solution with universal indicator paper. -Add 1cm3 of the unknown solution into a test tube, add 1cm3 of sodium carbonate into the solution, heat the test tube in a water bath, observe the presence of gas produced. Analysis of observations obtained Test Unknown organic compound 2,4-dinitrophenylhydrazine Tollens Reagent Potassium dichromate Sodium carbonate Solution turns yellow Silver mirror Solution turns green, makes universal indicator paper red No reaction Propanal Solution turns yellow No reaction No reaction No reaction Propanone No reaction No reaction No reaction Gas is produced Propanoic acid No reaction Silver mirror Solution turns green, makes universal indicator paper red No reaction Propan-1-ol No reaction Silver mirror Solution turns green, universal indicator paper turns green No reaction Propan-2-ol No reaction No reaction No reaction No reaction Methyl ethanoate Safety precautions and risk assessments Some of the chemicals used are irritant if not corrosive, therefore safety spectacles must be worn at all time during the practical investigation. At no point of the experiment should the person be sitting down, this is because hot water and fire is being used, and being sated would make escape slower. As all of the organic compounds used are extremely flammable, do not let the compounds near naked flame, and be very careful during heating, must use a hot water bath as a medium for heating. Bibliography -Cambridge Advance Science Chemistry 2, p25 for the reactions for 2,4-dinitrophenylhydrazine. -Heinemann Revise A2 Chemistry, p9 for the reactions for Tollens Reagent. -Heinemann Revise AS Chemistry, p56 for the reactions for alcohols.