Biology – Testing for biological molecules | e-Consult
Testing for biological molecules (1 questions)
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Procedure:
- Add a small drop of the sample to a conical flask.
- Add two drops of Benedict's reagent (a solution containing copper(II) ions in an alkaline solution) to the flask.
- Warm the mixture in a water bath at approximately 50-60°C for 5-10 minutes.
Expected Results:
- Positive Result: The solution will turn from blue to green, yellow, or orange. This indicates the presence of reducing sugars.
- Negative Result: The solution will remain blue. This indicates the absence of reducing sugars.
Chemical Basis: Reducing sugars contain a free aldehyde or ketone group. Upon heating with Benedict's reagent, these groups reduce the copper(II) ions (Cu2+) to copper(I) ions (Cu+). This reduction forms a reddish-brown precipitate of copper(I) oxide (Cu2O), which is responsible for the colour change. The more reducing sugars present, the more Cu2+ is reduced, resulting in a stronger colour change.