Question

The density of water at room temperature is 1.0 g/mL. How many molecules are there in a drop of water if its volume is 0.05 mL?

Answer 1

SOLUTION : Since density of water $=1 \cdot 0 g / mL$

$\therefore \quad$ Mass of onc drop of watcr $=$ volume $\times$ density $=0.05 \times 1 g =0.05 g$ No. of mole of water $=\frac{\text { mass }}{\text { mol. wt. }}=\frac{0 \cdot 05}{18}$ mole.

Hence, no. of molecules in one drop of water

$=\frac{0 \cdot 05}{18} \times 6.02 \times 10^{23} \text { molecules }= 1 . 6 7 \times 10^{21} \text { molecules. }$