Question

How can you prove that glucose contains 5 oh group?

Answer 1

Reaction with acetic anhydride $\ce{(CH3CO)2O}$
Glucose gives a penta ester with acetic anhydride, revealing that it has 5 hydroxyl groups.

Answer 2

Let us say we have 1 mole of Glucose having weight 180 gram.

After Acetylation , the weight of glucose increases by 210 gram because of attachment of 5 Acetyl groups ; each having weight of 43 gram and 5 Hydrogen atoms are also removed from the 5 -OH groups of Glucose.

The net weight gain = (43 x 5) - (1 x 5) = 210 gram

The removal of these 5 Hydrogen atoms Or the attachment of 5 Acetyl groups confirm the presence of 5 - OH groups in it.