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Organic observation exercise

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Introduction

Organic observation exercise - II In this exercise you will be assessed on your observations of a series of reactions and your ability to interpret these observations. You are provided with two liquids, X and Y, which are ISOMERS of each other and contain only the elements carbon, hydrogen and oxygen. Place about 5cm3 of 2, 4 - dinitrophenylhydrazine reagent in each of two tubes. To one add several drops of the compound X, to the other add several drops of compound Y. Compound X OBSERVATIONS INFERENCES The colourless compound X forms orange-yellow crystals when combined with 2, 4-DNPH 2, 4-DNPH reacts with carbonyl groups to give orange coloured precipitates. The test gave a positive result when it produced orange-yellow crystals. This identifies the presence of the reactive C=O bond and that compound X is either an aldehyde or a ketone. Compound Y OBSERVATIONS INFERENCES The orange coloured 2, 4-DNPH when combined with compound Y forms a faint yellow crystalline precipitate. 2, 4-DNPH reacts with carbonyl groups to give orange coloured precipitates. The test gave a positive result when it produced yellow crystals. This identifies the presence of the reactive C=O bond and that compound Y is either an aldehyde or a ketone. ...read more.

Middle

This time the oxidising agent is a complex of silver(I) ions, which are reduced to silver in the test forming a 'silver mirror'. This test shows that X is a good reducing agent and as aldehydes reduce an ammoniacal solution of silver nitrate to silver the compound is likely to be an aldehyde. RCHO + 2Ag+ + H2O RCO2H + 2Ag(s) + 2H+ Compound Y OBSERVATIONS INFERENCES The combination of silver nitrate with NaOH produces a murky brown solution, which after decantation and on the addition of ammonia dissolves the precipitate. Adding compound Y and heating in a water bath did not produce a visible colour change. Ketones cannot normally be oxidised and they do not react with Tollens' reagent. The reaction did not produce a visible colour change and so supports the theory that compound Y is the ketone, propanone. Place about 1cm3 of potassium manganate (VII) solution into each of two test tubes. To one add a few drops of compound X to the other a few drops of compound Y. Shake both tubes. Compound X OBSERVATIONS INFERENCES The solution of KMnO4 changes colour from purple to brown when compound X is added and a sharp a smell is produced. ...read more.

Conclusion

If it is an aldehyde then there should be no visible reaction. It is my intention to perform this devised to test to discover the possible identity of the compound. OBSERVATION Compound X produced a slight effervescence when it reacted with sodium bicarbonate. This produced a gas, which was colourless by nature and had no distinct smell. INFERENCE Although my results show the possible existence of a carboxylic acid it is known that after prolonged exposure to the air, the molecules of an aldehyde are oxidised to the carboxylic acid. This acid, which I suspect to be propanoic acid, would have sufficient strength to react with the NaHCO3 to produce CO2 gas and give a false indication as to the existence of the aldehyde. I still believe that compound X is an aldehyde. The following diagram shows the progression from a primary alcohol to aldehyde and finally to a carboxylic acid by oxidation: R-CH2-OH R-CHO R-COOH (primary alcohol) (aldehyde) (carboxylic acid) Use the information you have obtained from the other parts of this question to deduce structural formulae for compounds X and Y and give their systematic names. Structure of compound X: Systematic name for compound X: Propanal Structure for compound Y: Systematic name for compound Y: Propanone Chemistry Coursework Nick Curum Organic observation exercise - II 1 27/04/2007 ...read more.

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