describe and carry out a test to identify the presence of non-reducing sugars, using acid hydrolysis and Benedict’s solution

Sourav PanOctober 28, 2024

Answered

To test for the presence of non-reducing sugars, such as sucrose, you can use acid hydrolysis followed by Benedict’s test. Here’s a step-by-step guide on how to carry out this test:

Materials Needed:

• Sample solution (containing the suspected non-reducing sugar)
• Hydrochloric acid (HCl)
• Sodium hydroxide (NaOH) or sodium bicarbonate
• Benedict’s solution
• Test tubes
• Boiling water bath
• Dropper or pipette

Procedure:

1. Initial Benedict’s Test:
   • Add a small amount of Benedict’s solution to the sample solution in a test tube.
   • Place the test tube in a boiling water bath for 2–3 minutes.
   • Observe for any color change.
     • If there is no color change (solution remains blue), this suggests that no reducing sugars are present, so you can proceed to test for non-reducing sugars.
     • If a color change occurs (e.g., to green, yellow, orange, or red), this indicates the presence of reducing sugars, and the test for non-reducing sugars is not necessary.
2. Acid Hydrolysis:
   • Add a few drops of dilute hydrochloric acid (HCl) to a fresh sample of the solution in a test tube.
   • Heat the mixture in a boiling water bath for about 5 minutes to hydrolyze the non-reducing sugars (like sucrose) into their constituent reducing sugars (like glucose and fructose).
3. Neutralization:
   • After heating, carefully add sodium hydroxide (NaOH) or sodium bicarbonate to neutralize the acid, as Benedict’s solution requires a neutral or slightly alkaline environment to work properly.
   • Test with pH paper to ensure the solution is neutral.
4. Benedict’s Test (Second Round):
   • Add Benedict’s solution to the neutralized mixture.
   • Place the test tube back in the boiling water bath for 2–3 minutes.
5. Observe Results:
   • Positive result: The solution changes color (green, yellow, orange, or brick-red precipitate) indicating the presence of reducing sugars that were initially non-reducing sugars.
   • Negative result: The solution remains blue, indicating no non-reducing sugars were present.

Explanation:

The acid hydrolysis breaks down non-reducing sugars into reducing sugars, which can then react with Benedict’s solution to produce a color change, indicating their presence.