Core Practical 5: Investigate the oxidation of ethanol

Question 1

ethanol is

Answer 1

flammable

Question 2

acidified potassium dichromate(VI) is

therefore you should:

Answer 2

an oxidising agent, meaning it may cause other substances to burn more readily, even without a naked flame
it is both corrosive and carcinogenic

chemical resistant gloves should be worn, as well as eye protection

Question 3

the method for carrying out the oxidation of ethanol is:

Answer 3

-carefully add 20 cm3 of acidified potassium dichromate(VI) to a pear shaped flask and cool in an ice bath
-(to make the acidified potassium dichromate(VI), add 5cm3 of concentrated sulfuric acid to the K2Cr2O7)
-set up the flask for heating under reflux, but keep in the ice bath
-add some anti-bumping granules to the pear-shaped flask
-measure out 1cm3 of ethanol, and use a pipette to slowly add the ethanol drop-wise down the condenser
(propanol may be used instead for a less vigorous reaction)
-remove the ice-water bath and allow the flask to reach room temperature by leaving for 5 minutes
-use hot water from a kettle to make a hot water bath, and place the flask in the water bath, heating with a Bunsen burner
-maintain a boiling water bath for 20 minutes (you may need to add some more water)
-allow to cool, then set up the flask for distillation (simple) and distill until you collect 3-4cm3 of clear, colourless liquid

Question 4

the method for analysing the results for the experiment are:

Answer 4

• measure and record the pH using universal indicator paper, should be 3.5
• separate 1cm3 of the distillate and add some CaCO3 (quarter spatula) and observe effervescence (CO2) and dissolving
• add magnesium ribbon to 1cm3 o the distillate and observe effervescence (H2) and dissolving
• add 1cm3 Fehling’s solution to the distillate and warm in a water bath, the solution should remian blue, and NOT form a red precipitate
• add 1cm3 acidified K2Cr2O7 and heat at 60 degrees C in water bath. the mixture should remain orange and NOT change to green

Question 5

Write an equation for the reaction of the distillate with calcium carbonate:

Answer 5

2CH3COOH + CaCO3 → (CH3COO)2Ca + CO2 + H2O

Question 6

Write an equation for the reaction of the distillate with magnesium:

Answer 6

2CH3COOH + Mg → Mg(CH3COO)2 + H2

Question 7

Write an equation for the oxidation of ethanol to ethanoic acid:

Answer 7

CH3CH2OH + 2[O] → CH3COOH + H2O