A student used the following steps in testing for a non-reducing sugar. I. added Benedict's solution to the…

Analyzing the question: The test is for a non-reducing sugar such as sucrose. We need to know why dilute HCl is added and the solution boiled in step II.

The concept: Non-reducing sugars (e.g., sucrose) do not give a brick-red precipitate with Benedict's solution, because they have no free aldehyde or ketone group to reduce the copper(II) ions. That is why step I gives a negative result.

To show that the sugar is non-reducing, it must first be broken down into its reducing monosaccharides. This is done by acid hydrolysis:

Sucrose + H₂O → (dilute HCl, heat) → Glucose + Fructose

Both glucose and fructose are reducing sugars.

Step-by-step solution:

• Step I: Benedict's solution is added to the sugar, and no brick-red precipitate forms. This shows it is not a reducing sugar.
• Step II: Dilute HCl is added and the mixture is boiled. This hydrolyses the glycosidic bond and splits the sugar into simple reducing sugars.
• Step III: Sodium hydroxide is added to neutralise the acid, because Benedict's solution works only in alkaline conditions. The acid would otherwise interfere with the test.
• Step IV: Benedict's solution is added again and the mixture is heated. A brick-red precipitate now forms, which confirms a non-reducing sugar was originally present.

Checking the options:

• A. Oxidize: wrong. The acid does not oxidize the sugar. Benedict's solution is the oxidizing agent.
• B. Hydrolyse: correct.
• C. Dry: wrong. HCl does not dry anything here.
• D. Increase volume: wrong. This is not the purpose of the acid.

Answer: B. hydrolyse the sugar solution

Exam tip: Remember the sequence for non-reducing sugars: Hydrolyse (acid + heat) → Neutralise (alkali) → Test (Benedict's). If a question asks about the role of the acid, the answer is hydrolysis. If it asks about the role of NaOH, the answer is neutralisation.