This experiment demonstrated the catalytic oxidation of ethanol (~96% C2H5OH), using chromium(III) oxide (Cr2O3). Cr2O3 was obtained using the decomposition reaction of ammonium dichromate (NH4)2Cr2O7, see the experiment “Volcano”) just before the present experiment, as freshly prepared Cr2O3 has higher catalytic activity.
A few milliliters of ethanol was poured into a 0.5 liter conical flask. The flask was capped with a stopper and thoroughly shaken, as to fill the flask with ethanol vapor.
A test tube containing chromium(III) oxide was vigorously heated in a gas flame. The hot chromium(III) oxide was sprinkled into the flask filled with ethanol vapor. The flask became filled with the sparks of burning ethanol. The following stages of ethanol oxidation can be distinguished:
1) Ethanol is oxidized to ethanal (CH3CHO):
2C2H5OH(g) + O2(g) → 2CH3CHO(g) + 2H2O(l)
2) Ethanal is further oxidized to acetic acid (CH3COOH):
2CH3CHO(g) + O2(g) → 2CH3COOH(g)
3) Ethanol combusts on the surface of the hot catalyst (Cr2O3) yielding carbon dioxide and water:
C2H5OH(g) + 3O2(g) → 2CO2(g) + 3H2O(g)
3) VARIOUS: “Volcano”