Question

The number of water molecules present in a drop of water $(\text{volume}=0.0018\text{ml})$ at room temperature is:

• A. $6.023\times {10}^{19}$
• B. $1.084\times {10}^{18}$
• C. $4.84\times {10}^{17}$
• D. $6.023\times {10}^{23}$

Answer 1

The correct option is A $6.023\times {10}^{19}$

As we know that,

$\text{Density}=\frac{\text{mass}}{\text{volume}}$

$\Rightarrow \text{mass}=\text{density}\times \text{volume}$

Density of water $=1g/ml$

Volume of water $=0.0018mL\left(\text{Given}\right)$

$\therefore$ Mass of $0.0018mL$ water $=1\times 0.0018=0.0018gm$

Molar mass of water $=18gm/mol$

Number of moles in $0.0018gm$ of water $=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{0.0018}{18}=0.0001\text{mole}$

As we know that,

Number of molecules of water in $1$ mole $=6.022\times {10}^{23}\text{molecules}$

$\therefore$ Number of molecules of water in $0.0001$ mole $=6.022\times {10}^3\times 0.0001=6.023\times {10}^{19}$

Hence, the number of water molecules present in a drop of water $(\text{volume}=0.0018ml)$ at room temperature are $6.023\times {10}^{19}$.