Question

Calculate the number of He atoms in (i) 52 u, (ii) 52 g, (iii) 52 moles of He. Atomic weight of He is 4 u.

Answer 1

(i) Atomic weight of Helium = 4, i.e. 4 u is mass of 1 atom, 52 u is mass of 1/4 × 52 = 13 atoms. 

(ii) 4 g of He contains 6.022 × 10²³ He atoms / 52 g of He contains ?

(6.022 x 10²³ x 52)/4 = 7.8286 × 10²³ atoms. 

(iii) 1 mole of He contains 6.022 × 10²³ atoms, 52 moles of He contains 52 × 6.022 × 10²³ = 3.131 × 10²³ atoms.