The Dehydration of Ethanol

Introduction

Alcohols can undergo reactions in which water is removed from them to give a new class of compounds - called alkenes. This reaction requires a dehydrating agent such as concentrated sulphuric acid, phosphoric acid or aluminium oxide. This experiment will use aluminium oxide, Al2O3, as it is an easily managed solid.

Diagram

Method

Place a small ball of wire wool in the bottom of a thick walled Pyrex test tube. Using a dropping pipette add just enough ethanol to the wire wool to saturate it. Pour off any excess, and pack the rest of the test tube, to a depth of about two inches, with aluminium oxide. Clamp the test tube in a horizontal position near the end of the test tube, and attach a delivery tube etc. as in the diagram above.

Heat the aluminium oxide in the test tube and after a few minutes collect the gas produced in upside down test tubes. You should collect at least two test tubes of gas, placing a bung in them after collection, for the following tests.

N.B.: make sure that you remove the delivery tube from the beaker of water before you remove the Bunsen burner flame from the test tube, otherwise water will suck back into the test tube.

Note down all your observations during this reaction.

Tests on the gaseous product

(i) To a test tube of gas add about 5 drops of bromine water, Br2(aq), replace the bung on the tube and shake well. Note the original and final colour of the solution.

(ii) To a test tube of gas add about 5 drops of potassium manganate(VII) solution, KMnO4(aq), replace the bung on the tube and shake well. Note the original and final colour of the solution.