Question

Calculate the number of molecules in $0.71\text{g}$ of chlorine gas. Take Avogadro's number as $6\times {10}^{23}$.

Answer 1

Step 1: Given information

• Mass of chlorine $\left({\mathrm{Cl}}_2\right)$ gas is $0.71\text{g}$
• Avogadro's number is $6\times {10}^{23}$

Step 2: Calculate the Number of molecules

The molecular mass of chlorine gas is $71\text{g}$.

$71\text{g}$ of ${\mathrm{Cl}}_2$ contains $6\times {10}^{23}$ molecules.

$0.71\text{g}$ of ${\mathrm{Cl}}_2$ contains $\frac{6\times {10}^{23}}{71}\times 0.71{\text{=6×10}}^{21}\text{molecules}$

Hence, the number of molecules in $0.71\text{g}$ of chlorine gas is ${\mathrm{6\times 10}}^{21}\text{molecules}$.