Reaction of Sodium with Organic Compounds
Let's take a look at this question:
To determine the moles of hydrogen evolved we need to know the 3 functional groups that will react with sodium metal.
1. Alcohols to form alkoxide
ROH + Na → RO-Na+ + 1/2 H2(g)
2. Phenols to form phenoxide
PhOH + Na → PhO-Na+ + 1/2 H2(g)
3. Carboxylic acids to form carboxylate
RCOOH + Na → RCOO-Na+ + 1/2 H2(g)
All these functional groups undergo deprotonation or donate their proton.
Hence the reaction with sodium is considered as acid-base or neutralisation with respect to organic compound.
Here's my video lesson on how to compare acidity of these organic compounds.
Finally we can now look back at citric acid.
Citric acid contains 3 carboxylic acid groups and 1 alcohol group.
For each of these functional groups, one mol of functional group will form 0.5 mol of H2 gas.
Hence 1 mol citric acid will produce 2 mol H2(g). [Answer = B]
Topic: Carboxylic Acid, Organic Chemistry, A Level Chemistry, Singapore
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