Question

reaction between sodium thiosulphate and iodine using starch as indicator

Answer 1

The reaction between sodium thiosulphate (Na₂S₂O₃) and iodine ( I₂) using starch indicator is given below: -

I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq)

This is an example of iodometric titration or iodometry.

Here, starch acts as the end-point between sodium thiosulphate and iodine. When dissolved in water, starch solution is colourless. However,in presence of iodine, it turns blue to black.