Question

In limit test of iron, purple colour is due to formation of

Answer 1

Limit test of Iron is based on the reaction of iron in ammonical solution with thioglycollic acid in presence of citric acid to form iron thioglycolate which is pale pink to deep reddish purple in color.

Answer 2

In limit test of iron, purple colour is due to formation of ferrous thioglycolate.

• Limit test of iron is semi quantitative or quantitative test indicating presence of impurities in substance.
• The test results in pale pink to dark colour of reddish purple, which on being darker than standard, indicates presence of impurities.
• Thioglycollic acid used in the reaction is required for oxidation of iron.