Question

What is the mass of a water molecules in gram? How many molecules are present in one drop of pure water which weighs $0.05g$? If the same drop of water evaporates in one hour, calculate the number of molecules leaving the liquid surface per second.

Answer 1

$\text{Mass of water molecule =}\frac{18g}{N_A}=\frac{18}{6.023\times {10}^{23}}=2.988\times {10}^{-23}g\text{In 18 gm there are 6.023}\times {10}^{23}\text{molecules}\text{0.05 there are}\frac{0.05}{18}\times 6.023\times {10}^{23}\text{= 1.67}\times {10}^{21}\text{molecules}$