Chapter 5, Problem 5.155QP

A mixture contained calcium carbonate, CaCO₃, and magnesium carbonate, MgCO₃. A sample of this mixture weighing 7.85 g was reacted with excess hydrochloric acid. The reactions are

$\begin{array}{l}{\text{CaCO}}_{\text{3}}(g)+2\text{HCL(}aq\text{)}\to \hfill \\ \begin{array}{l}{\text{CaCl}}_{\text{2}}(aq)+{\text{H}}_{\text{2}}\text{O(}I{\text{)+CO}}_{\text{2}}\text{(g)}\\ {\text{MgCO}}_{\text{3}}(s)+2\text{HCL(}aq\text{)}\to \\ {\text{MgCl}}_{\text{2}}(aq)+{\text{H}}_{\text{2}}\text{O(}I{\text{)+CO}}_{\text{2}}\text{(g)}\end{array}\hfill \end{array}$

If the sample reacted completely and produced 1.94 L of carbon dioxide, CO₂, at 25°C and 785 mmHg, what were the percentages of CaCO₃ and MgCO₃ in the mixture?