Question

The percentage of available chlorine in a pure bleaching powder $\left(\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2\right)$ sample is ______

Answer 1

Part 1: Definition of Percentage by weight

• It is defined as the mass percent composition of an element in a compound
• It can be abbreviated as $\frac{\mathrm{w}}{\mathrm{W}}\%$

$\mathrm{Percentage}\mathrm{by}\mathrm{weight}=\{\frac{\mathrm{weight}\mathrm{of}\mathrm{the}\mathrm{element}}{\mathrm{weight}\mathrm{of}\mathrm{compound}}\mathrm{x}100\}\%$

Part 2: Percentage of chlorine in bleaching powder

• Let us calculate the mass of bleaching powder $\left(\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2\right)=1\times \mathrm{mass}\mathrm{of}\mathrm{Ca}+2\times \mathrm{mass}\mathrm{of}\mathrm{Cl}+2\times \mathrm{mass}\mathrm{of}\mathrm{O}$

$=1\times 40+2\times 35.5+2\times 16$

$=143\mathrm{g}$

• The total mass of chlorine$=2\times 35.5=71\mathrm{g}$
• Therefore the percentage of chlorine in bleaching powder is:

$$\begin{gathered} \mathrm{Percentage}\mathrm{by}\mathrm{weight}=\{\frac{\mathrm{weight}\mathrm{ofchlorine}}{\mathrm{weight}\mathrm{of}\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2}\mathrm{x}100\}\% \\ =\{\frac{71}{143}\mathrm{x}100\}\%=49.6\% \end{gathered}$$

Conclusion: The percentage of available chlorine in a pure bleaching powder $\left(\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2\right)$ sample is 49.6%