Chapter 5, Problem 93RQ

A sample of a copper ore with a mass of 0.4225 g was dissolved in acid. A solution of potassium iodide was added, which caused the reaction

${\text{2Cu}}^{\text{2+}}\text{(}aq{\text{)+5I}}^{\text{-}}\text{(}aq\text{)}\to {\text{I}}_{\text{3}}{}^{\text{-}}\text{(}aq\text{)+2CuI(}s\text{)}$

The ${\text{I}}_{\text{3}}{}^{\text{-}}$ that formed reacted quantitatively with exactly 29.96 mL of 0.02100 M ${\text{Na}}_{\text{2}}{\text{S}}_{\text{2}}\text{O3}$ according to the following equation.

${\text{I}}_{\text{3}}{}^{\text{-}}\text{(}aq{\text{)+2S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{\text{2-}}\text{(}aq\text{)}\to {\text{3I}}^{\text{-}}\text{(}aq{\text{)+S}}_{\text{4}}{\text{O}}_{\text{6}}{}^{\text{2-}}\text{(}aq\text{)}$

(a) What was the percentage by mass of copper in the ore?

(b) If the ore contained ${\text{CuCO}}_{\text{3}}$, what was the percentage by mass of ${\text{CuCO}}_{\text{3}}$ in the ore?