Problem 1

To determine the solubility product of copper(II) iodate,

\ce{Cu(IO3)2}

, a saturated aqueous solution of

\ce{Cu(IO3)2}

at 25 °C is analysed by iodometric titration in acidic solution: an excess of iodide is added and the liberated iodine is titrated with sodium thiosulphate.

30.00\ \mathrm{cm^3}

of a 0.100 M sodium thiosulphate solution are needed for

20.00\ \mathrm{cm^3}

of the saturated solution. (1.1) Write the sequence of balanced equations for the reactions described. (1.2) Calculate the initial concentration of

\ce{Cu^{2+}}

and the solubility product of copper(II) iodate. Activity coefficients can be neglected.

Step 2 of 3: Stoichiometry of the titration

← Previous Next →

n(\ce{S2O3^{2-}}) = 0.100 \times 0.03000 = 3.00\times10^{-3}\ \mathrm{mol};\quad n(\ce{I2}) = 1.50\times10^{-3}\ \mathrm{mol};\quad n(\ce{Cu^{2+}}) = 1.50\times10^{-3} \times \tfrac{2}{13} = 2.31\times10^{-4}\ \mathrm{mol}

Analysis

From $\ce{I2} + 2\ce{S2O3^{2-}}$ , $n(\ce{I2}) = n(\ce{S2O3^{2-}})/2 = 1.50\times10^{-3}$ mol. The net equation produces $13\ \ce{I2}$ per $2\ \ce{Cu^{2+}}$ , so $n(\ce{Cu^{2+}}) = 1.50\times10^{-3}\times 2/13 = 2.31\times10^{-4}$ mol in the $20.00\ \mathrm{cm^3}$ aliquot.