Question

Role of thioglycolic acid in limit test for iron

Answer 1

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When a pale pink to deep reddish purple colour is formed due to the ferrous thioglycote complex. The iron free citric acid is used to complex metal cations other than iron if any.

Answer 2

Thioglycolic acid is also called citric acid.

• In the limit test of iron, iron reacts with citric acid in ammoniacal solution to form pink-reddish purple coloured iron thioglycolate.
• In this reaction, citric acid acts as a chelating agent.
• It binds the iron to form a soluble complex. It also prevents the formation of ferrous hydroxide due to the precipitation of ammonia from the ammoniacal solution.