Unit A23 4.8 Carboxylic acids

Question 1

4.8.3 - Preparing a carboxylic acid from an alcohol

Answer 1

• Add concentrated sulfuric acid to water in a pear shaped/round bottomed flask.
• Swirl the solution and cool the flask to dissipate the heat and to prevent spitting.
• Add potassium dichromate(VI) solution and swirl the mixture.
• Add anti-bumping granules.
• Attach a vertical condenser.
• Add the alcohol slowly, down the condenser, to the acidified potassium dichromate(VI) solution, cooling the reaction flask in a water bath.
• Heat the mixture under reflux.
• Distil off the acid.

For information on reflux and distillation, see AS practical document.

Question 2

4.8.5 - Carry out test tube reactions of a carboxylic acid with sodium carbonate, sodium hydroxide and aqueous ammonia and measure the pH changes

Answer 2

• Place 1 cm3 of the carboxylic acid in a boiling tube
  • Record the pH using pH paper
  • Add a spatula measure of sodium carbonate and record observations
  • Record the pH using pH paper
• Repeat the experiment using 1 cm3 of sodium hydroxide solution instead of sodium carbonate
  • Repeat the experiment using 1 cm3 of aqueous ammonia instead of sodium carbonate.