Question

Calculate the number of atoms in each of the following 

(i) 52 moles of Ar

(ii) 52 u of He

(iii) 52 g of He

Answer 1

(i) 1 mol of He contains 6.023 x 10²³ He atom

52 mol of He contains = {6.023 x 10²³ x 52}/{1} He atom

= 3.132 x 10^-25 He atom

(ii) 1 molecule of He = 4 u   [atomic mass of He = 4]

Therefore, 4 u = 1 He atom

52 u = 1 x {52 u}/{4 u} He atom = 13 He atom

(iii) 1 mol of He ≡ 4 g ≡ 6.023 x 10²³ He atom

Thus 4 g of He contains 6.023 x 10²³ He atom

52 g of He contains = 6.023 x 10²³ x 52/4 He atom

= 7.8286 x 10^-24 He atom