Question

A solution which tested negative for reducing sugars was thought to contain sucrose and protein. Describe how you would find out whether this was so (6 marks)

Accepted Answer

mix equal volumes of solution and dilute hydrochloric acid;

boil in a water bath (for 2 minutes) to hydrolyse sucrose (to glucose and fructose);

mix with equal volumes of Benedict’s reagent;

boil in water bath (for 2 minutes);

if brick red precipitate appears then sucrose is present;

mix equal volumes of solution and (dilute/5 %) sodium hydroxide

run dilute/1% copper sulphate solution into the solution

a purple ring at the interface indicates protein is present;

Solution Sucrose Mix Equal Volumes Boil Water Bath