Reactions of aldehydes and ketones. The purpose of this experiment is to compare some reactions of ethanal and propanone.

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                    Date:   8/11/2011

Exp. No.:            25

Title:                Reactions of aldehydes and ketones

Aim:        The purpose of this experiment is to compare some reactions of ethanal and propanone.

Introduction:  In this experiment, ethanal and propanone were chosen as they are relatively safe. The structures of the 2 compounds are as follow:

                                  

                       Ethanal                  Propanone

            In this experiment, we are going to investigate the following reactions of these 2 compounds:

  1. Addition
  2. Condensation
  3. Oxidation
  4. Iodoform reaction

Apparatus and chemicals:

Apparatus:  Safety spectacles, hot water bath, cold water bath, test tubes, beakers

Chemicals:  Saturated hydrosulphite solution , 2,4-dinitrophenylhydrazine solution, 0.1M potassium dichromate solution, 1M sulphuric acid, Fehling’s reagent (Fehling solution A + Fehling solution B), 0.05M Silver nitrate solution, 2M sodium hydroxide solution, 2M ammonia solution, iodine solution 10% (in KI(aq))

Procedures:

Part 1: Addition reaction with sodium hydrogensulphite

  1. About 2 cm3 of saturated sodium hydrogensulphite solution was added into a test tube.
  2. The test tube was put into a cold water bath.
  3. Similar volume of ethanal was added drop by drop into the test tube.
  4. The experiment was repeated using propanone instead of ethanal.

Part 2: Condensation reaction with 2,3-dinitrophenylhydrazine

  1. About 1 to 2 drops of ethanal was added into a test tube.
  2. The test tube was put into a warm water bath.
  3. About 2 cm3 of 2,4-dinitrophenylhydrazine was added into the test tube.
  4. The experiment was repeated using propanone instead of ethanal.

Part 3: Oxidation reaction

  1. With acidified potassium dichromate
  1. 5 drops of ethanal, 2 drops of potassium dichromate solution and 10 drops of dilute sulphuric acid were added into a test tube.
  2. The test tube was shook gently and was put into a warm water bath.
  3. The experiment was repeated using propanone instead of ethanal.

  1. With Fehling’s solution
  1. About 1 cm3 of Fehling’s solution A into a test tube.
  2. Fehling’s solution B was added drop by drop until the precipitate just redissolved.
  3. About 7 drops of ethanal was added into the test tube and the tube was shook gently.
  4. The test tube was put into a hot water bath for 5-10 minutes (until no further colour change was observed).
  5. The experiment was repeated using propanone instead of ethanal.

  1. With Tollens’ reagent
  1. About 1 cm3 of 0.05M silver nitrate solution was added into a very clean test tube.
  2. 3 to 4 drops of sodium hydroxide solution were added into the test tube.
  3. Ammonia solution was added drop by drop until the precipitate just redissolved.
  4. 1-2 drops of thanal were added into the test tube and the tube was shook gently.
  5. The test tube was placed in a warm water bath and a few minutes.
  6. The experiment was repeated using propanone instead of ethanal.

Part 4: Iodoform test

  1. 5 drops of ethanal and 1 cm3 of iodine solution were added into a test tube.
  2. The test tube was shook gently and sodium hydroxide solution was added drop by drop until the colour of iodine just disappeared with a straw-coloured solution remaining.
  3. The experiment was repeated using propanone instead of ethanal.
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Observations: 

  1. Dilute sulphuric acid had a irritating odour.
  2. Propanone had a pungent odour while ethanal had a pungent and fruity odour.
  3. Dilute sulphuric acid and sodium hydroxide solution were colourless.

Part 1

Adding sodium hydrogensulphite solution

  1. For ethanal, the solution turned milky and white spongy precipitate was formed. After pouring away the solution, there were white solid crystal remaining in the test tube.
  2. For propanone, there wer 2 colourless immisible layers formed.
  3. Both of the solution became turned warm.

Part 2

Treating with 2,4-dinitrophenylhydrazine

  1. 2,4-dinitrophenylhydrazine solution was ...

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This is a fantastic, extremely detailed account with excellent chemistry used throughout. I would highly recommend it to anyone studying the identification of aldehydes or ketones This piece of work is 5 stars out of 5