Question

If 0.2 mole of the calcium carbonate is required, then how many grams of it should be taken?​ [2 marks]

Answer 1

Given:

• Moles of ${\mathrm{CaCO}}_3$ = 0.2 moles​

The number of moles is calculated as follows:
$\mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Mass}\mathrm{of}{\mathrm{CaCO}}_3\left(m\right)}{\mathrm{Molar}\mathrm{mass}\mathrm{of}{\mathrm{CaCO}}_3\left(M\right)}$
[0.5 mark]

Molar mass is calculated as follows:

$\begin{array}{ccc}\mathrm{Molar}\mathrm{mass}\mathrm{of}{\mathrm{CaCO}}_3\left(M\right)& =& \mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{Ca}+2\left(\mathrm{Atomic}\mathrm{mass}\mathrm{of}C\right)+3\left(\mathrm{Atomic}\mathrm{mass}\mathrm{of}O\right)\\ & =& 40+12+3\left(16\right)\\ & =& 40+12+48\\ & =& 100u\end{array}$[1.0 mark]

The mass required to have 0.2 mole is calculated as follows:

$\begin{array}{ccc}0.2& =& \frac{\mathrm{Mass}\mathrm{of}{\mathrm{CaCO}}_3\left(m\right)}{100}\\ \mathrm{Mass}\mathrm{of}{\mathrm{CaCO}}_3\left(m\right)& =& 0.2\times 100\\ & =& 20g\\ & & \end{array}$
[0.5 mark]

Thus, the mass required to have 0.2 moles of the calcium carbonate is 20 g.