Oxidation of alcohols and preparative techniquesEdexcel International A Level Chemistry: Subtopic test

1. 1
   A student warms propan-2-ol with acidified potassium dichromate(VI) solution and notes the colour change. She then repeats the test with 2-methylpropan-2-ol.

   (a)

   What is the organic product when propan-2-ol is oxidised by acidified potassium dichromate(VI)?

   [1 mark]

   • APropanone
   • BPropanal
   • CPropanoic acid
   • DPropene

   (b)

   What colour change is seen when propan-2-ol is oxidised?

   [1 mark]

   • AGreen to orange
   • BColourless to blue
   • COrange to yellow
   • DOrange to green

   (c)

   State what is seen with 2-methylpropan-2-ol and explain why.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Propan-1-ol is oxidised using acidified potassium dichromate(VI). In one experiment the product is distilled off as it forms; in a second experiment the mixture is heated under reflux.

   (a)

   Which procedure gives propanal as the main product?

   [1 mark]

   • AHeat under reflux with excess acidified dichromate(VI)
   • BHeat with concentrated phosphoric acid
   • CAdd acidified dichromate(VI) and distil off the product as it forms
   • DHeat with ethanolic potassium hydroxide

   (b)

   Which observation confirms that propanoic acid is present in the product of the reflux experiment?

   [1 mark]

   • AA brick-red precipitate with Fehling's solution
   • BEffervescence with sodium carbonate solution
   • CThe orange solution turns green
   • DA cream precipitate with silver nitrate

   (c)

   Write an equation, using [O] for the oxidising agent, for the oxidation of propanal to propanoic acid, and state the colour change of the oxidising agent.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In Core Practical 7 a student oxidises propan-1-ol. Boiling temperatures: propan-1-ol 97 °C, propanal 49 °C and propanoic acid 141 °C. The first preparation is designed to give propanal and the second to give propanoic acid.

   (a)

   Explain why propanal can be isolated by distilling it out of the mixture as it forms.

   [3 marks]

   (b)

   Describe how propanoic acid is prepared, explaining why the reaction mixture is heated under reflux, and state the temperature at which the final product is collected.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has three unlabelled bottles containing butan-1-ol, butan-2-ol and 2-methylpropan-2-ol. She uses warm acidified potassium dichromate(VI), followed by Fehling's solution and sodium carbonate on the products, to identify each alcohol.

   (a)

   Describe how the student can identify each alcohol, stating the observations she would make.

   [6 marks]

   (b)

   The student wants a pure sample of butanoic acid from butan-1-ol. Describe the method, including purification, and explain the purpose of each stage.

   [6 marks]

   Total for question 4: 12 marks

End of questions