Question

How many molecules are present in
a) 9 g of water
b) 17 g of ammonia

Answer 1

1) Molar mass of H₂O = 18 g mol^-1
Given mass of H₂O = 9 g
18 g of water contains = 6.022$\times$10²³ molecules
9 g of water contains = $\frac{6.022\times {10}^{23}}{18}\times 9=3.011\times {10}^{23}molecules$

2) Molar mass of ammonia = 17 g mol^-1
Given mass of ammonia = 17 g
17 g of ammonia contains = 6.022$\times$10²³ molecules