Blackboard chalk is a mixture of limestone and gypsum. A piece of blackboard chalk weighing \(5.42 g\) was immersed in \(HCl\). The \(CO _{2}\) produced weighed \(1.11 g\). What is the percentage of limestone in the calk?
A. \(67.0 \%\) B. \(53.3 \%\) C. \(50.8 \%\) D. \(46.5 \%\)
Correct Answer: D
Explanation
\(CaCO _{3( e )}+2 HCl _{(\text {an) }} \rightarrow CaCl _{2(\infty)}+ H _{2} O _{(n+1}+ CO _{2(\text { a) }}\) Molar mass of \(CaCO _{3}=100 gmol ^{-1}\) Molar mass of \(CO _{2}=44 gmol ^{-1}\)ccording to the equation, 1 mole of \(CaCO _{3}\) produces 1 mole of \(CO _{2}\). Mole of \(CO _{2}=\frac{1.11 g }{44 gmol ^{-1}}\) \(\Rightarrow 0.02523 mol\) Therefore, mole of \(CaCO\), \(\Rightarrow 0.02523 mol\) Mass of \(CaCO _{3}\) present \(=(0.02523 \times 100) g =2.523 g\) \(\%\) of \(CaCO _{3}=\frac{2.523 g }{5.42 g } \times 100 \%\) \(=46.55 \%\)