Question

Which of the following pairs can be distinguished by Fehling's solution ?

• A. Glucose and fructose
• B. Glucose and sucrose
• C. Methanal and ethanal
• D. Hydroxypropanone and benzaldehyde

Answer 1

The correct option is B

Glucose and sucrose

Glucose is a hemiacetal, so in presence of a base (alkaline medium is provided by Fehling's solution. It can develop - CHO group in the form of open-chain structure which responds to Fehling's solution. Sucrose is a glycoside (acetal), i.e. it's hemiacetal -OH groups (one due to glucose and another due to - fructose) are not free, so it can't attain - CHO group. Hence it will not respond to Fehling's solution.