Question

A 2M 1 liter solution of Copper Sulphate is titrated with a 2M solution of KI. The amount of KI solution required was 2 liters. What is the amount of sodium thiosulphate required to back titrate the iodine formed to iodide?

Answer 1

In the iodometric titration, the substance to be estimated (such as ozone) reacts with iodide ion to liberate iodine.

$O_3+2I^{-}\to I_2+O_2+O^{2-}$

The liberated iodine is estimated with sodium thiosulphate solution.

$I_2+2S_2{O}_3^{2-}\to 2I^{-}+S_4{O}_6^{2-}$

Another example is as shown below:

The titration of $C{u}^{2+}$ with $I^{-}$

$2C{u}^{2+}+4I^{-}\to 2CuI\left(s\right)+I_2$

$2N{a}_2{S}_2{O}_3+I_2\to S_4{O}_6^{2-}+2I^{-}$.

Therefore, $x$ is $N{a}_2{S}_2{O}_3$ and its molar mass is $158$ g/mol.