4
Estimation of Copper by Iodometery
Aim
To estimate the amount of copper present in 100 ml of the given solution by using approximately 0.05N sodium thiosulphate (hypo) solution.
Principle
The estimation is based on iodometric titration. Hypo is standardised by titrating with standard potassium dichromate solution, which liberates iodine from potassium iodide in an acidic medium.
K2Cr2O7 + 7H2SO4 + 6KI → 4K2SO4 + Cr2(SO4)3 + 7H2O + 3I2
Copper sulphate reacts with potassium iodide liberating iodine.
2CuSO4 + 4KI → 2K2SO4 + 2Cu + 2I2
The liberated iodine is titrated against hypo using starch as the indicator.
2Na2S2O3 + I2 → Na2S4O6 + 2NaI
The starch indicator forms a violet blue colour with iodine. The disappearance of the violet blue colour ...
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