Core practical 5

Question 1

why do we add anti bumping granules ?

Answer 1

for smoother and more even boiling

Question 2

why must we slowly add the ethanol down the reflux condenser ?

Answer 2

because it slows the reaction down as it is a very vigorous reaction

Question 3

outline the process of oxidising ethanol

Answer 3

ethanol is oxidised by heating under reflux using excess acidified sodium dichromate (VI). Product is then distilled off and tested to confirm its identity

Question 4

give the equation for the oxidisation of ethanol with an oxidising agent

Answer 4

CH3CH2OH + 2 [O] -> H2O + CH3COOH

Question 5

procedure for the oxidisation of ethanol

Answer 5

Carefully add 20 cm3 of acidified sodium dichromate
solution to a 50 ml pear-shaped flask. Cool the flask in
an ice-water bath.
2. Set the flask up for reflux (see fig A) keeping it in the
ice-water bath.
3. Place a few anti-bumping granules into the pear shaped flask.
4. Measure out 1 cm3 of ethanol.
5. Using a pipette, add the ethanol a few drops at a time
down the reflux condenser. This must be done slowly.
Allow for the reaction to subside after each addition
before adding more.
6. When all of the ethanol has been added, remove the
ice-water bath and allow to warm to room temperature
(approximately 5 minutes).
7. Position the flask in a hot water bath using water from a
kettle. Light a Bunsen burner and maintain a boiling
water bath for 20 minutes. Allow the apparatus to cool.
8. Distil your product using the apparatus shown (see fig
B). Collect 3-4cm3 of clear, colourless liquid.

Question 6

explain the results of the tests involving acidified potassium dichromate and Fehling’s solution

Answer 6

• there is no change with acidified potassium dichromate as all the ethanol is oxidised.
  -there is no change with Fehling’s solution as oxidation goes to completion – any ethanol made is oxidised to ethanoic acid as it cannot leave the apparatus