Question

A drop of water is about $0.05$ $mL$. The density of water at room temperature is about $1.0$ $gm{L}^{-1}$. The number of water molecules present in a drop of water are:

• A. $1.67\times {10}^{21}{H}_{2}O$ molecules
• B. $1.67\times {10}^{26}{H}_{2}O$ molecules
• C. $1.806\times {10}^{23}{H}_{2}O$ molecules
• D. $1.806\times {10}^{21}{H}_{2}O$ molecules

Answer 1

The correct option is A $1.67\times {10}^{21}{H}_{2}O$ molecules

$d=\frac{m}{v}$ or mass of $0.05$ $mL$ water

$=0.05mL$ $\times 1.0$ $g$ $m{L}^{-1}$ $=0.05$ $g$ $H_{2}O$

Moles of $H_{2}O=\frac{0.05}{18}mol{H}_{2}O$

$=\frac{6.023\times {10}^{23}\times 0.05}{18}$

$=1.67\times {10}^{21}{H}_{2}O$ molecules