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2. Oxidation of alcohols This package has been written to help you to have a better understanding of the oxidation of ethanol. You can help to improve the quality of your drawings by assessing the work of some of the 2001 A Level students. Start

3. answer Student m Student J Drawing apparatus that works! Task 1: Students were asked to draw a labelled apparatus that could be used to oxidise ethanol to ethanal only. They should have included any special precautions necessary and assumed that the ethanal would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC (6 marks) Which student was correct? on to task 2

4. The potassium dichromate(VI) must beacidified Student m Ethanol is oxidised first to ethanal 3CH3CH2OH(l) + Cr2O72-(aq) + 8H+(aq) back to task 1 3CH3CHO(aq) + 2Cr3+(aq) + 7H2O(l) on to task 2 To be sure that further oxidation is prevented, the ethanal should be distilled from the reaction mixture as soon as it is formed.

5. answer Student J Student C Drawing apparatus that works! Task 2: Students were then asked to draw a labelled apparatus that could be used to fully oxidise ethanol without separating it from the reaction mixture. Special precautions were again to be considered. The ethanoic acid would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC. (5 marks) Which student’s diagram is better? back to task 1

6. Student J Overall, excess oxidising agent must be usedto make sure all the ethanol & ethanal is oxidised to ethanoic acid now see if you can assess some students’ diagrams 3CH3CHO(aq) + Cr2O72-(aq)+ 8H+(aq) 3CH3COOH(aq) + 2Cr3+(aq) + 4H2O(l) So to oxidise ethanol directly to ethanoic acid, a reflux apparatus must be used

7. Drawing apparatus that works! Task 1: Draw a labelled apparatus that could be used to oxidise ethanol to ethanal only. Include any special precautions necessary. Assume that the ethanal would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC (6 marks) How many marks you would give for each of these diagrams? Explain your allocation of marks in the empty boxes. (Press escape to type, then click to continue.) Student G Ethanol & potassium dichromate answer

8. Drawing apparatus that works! Task 1: Draw a labelled apparatus that could be used to oxidise ethanol to ethanal only. Include any special precautions necessary. Assume that the ethanal would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC (6 marks) Student G Answer ethanol & potassium dichromate (1)  no acid used (essential for the oxidation process) safe heating (1)  student can’t be sure that the ethanal wouldn’t be contaminated with ethanol  gas syringe is not gas tight, & if it was, the bung might come out !  is 22oC really hot enough? Ethanol & potassium dichromate

9. Drawing apparatus that works! Task 1 continued: Draw a labelled apparatus that could be used to oxidise ethanol to ethanal only. (6) Student M Student m answers

10. Drawing apparatus that works! Task 1 continued: Draw a labelled apparatus that could be used to oxidise ethanol to ethanal only. (6) Student M Answer ethanol & acidified potassium dichromate (2) safe heating (1)  ethanal condensed but will it evaporate again?  is 21oC really hot enough? Student m Answer ethanol & acidified potassium dichromate (VI) (2) controlled & safe heating of reaction mixture (1) thermometer ensures that distillation can be stopped before unreacted ethanol is collected (1) ethanal condensed and collected as a liquid (2) On to task 2

11. Drawing apparatus that works! Task 2: Draw a labelled apparatus that could be used to fully oxidise ethanol without separating it from the reaction mixture. Include any special precautions necessary. The ethanoic acid would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC.(5 marks) How many marks you would give for each of these threediagrams? Explain your allocation of marks in the boxes. Student C answer

12. Drawing apparatus that works! Task 2: Draw a labelled apparatus that could be used to fully oxidise ethanol without separating it from the reaction mixture. Include any special precautions necessary. The ethanoic acid would boil off at a temperature higher than 21oC. Ethanol’s Bp. is 79 oC.(5 marks) How many marks you would give for each of these threediagrams? Explain your allocation of marks in the boxes. Student C Answer ethanol & acidified (1) potassium dichromate (VI) (1) excess oxidising agent should be used  the heating method is dangerous in this case because of a flying bung and then a possible fire !  what is the thermometer for ?

13. Drawing apparatus that works! Task 2 continued: Draw a labelled apparatus that could be used to oxidise ethanol completely to ethanoic acid. (5) Student B Student J answers

14. Drawing apparatus that works! Task 2 continued: Draw a labelled apparatus that could be used to oxidise ethanol completely to ethanoic acid. (5)  see diagram below for how to draw a reflux condenser ! Answer ethanol & acidified (1) potassium dichromate(VI) (1) excess oxidising agent should be used attempt to reflux safely (1)  ethanol will escape Student B Answer ethanol & excess (owtte) (1) acidified (1) potassium dichromate (VI) (1) safe heating (1) under reflux (1) ensures conversion of ethanol to ethanoic acid (careful heating by Bunsen is acceptable) Student J

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