Question 15
Benedict's solution is added to a glucose solution and to a sucrose solution, and both are heated. What is the difference?
The right answer is the one marked above.
Glucose runs through the colour change straight away: blue → green → yellow → orange → a brick red precipitate. Sucrose shows no change at all until a few drops of dilute sulphuric acid are added and it is heated again — then the same colour change follows.
The acid splits the sucrose into its two monosaccharides, and it is those that Benedict's solution reacts with. Monosaccharides and some disaccharides respond directly; sucrose needs the extra step.