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:

(i)  52 moles of Ar

The number of atoms present in 52 mol of Ar can be calculated as follows.

1 moles of Ar = 6.022×10²³ atoms of Ar

52 moles of Ar = 52 x 6.022 x 10²³

∴ 52 moles of Ar = 3.13144 × 10²⁵

(ii) 52 u of He

The atomic mass of He is 4 amu.

52 u of He will contain  52/4  = 13 atoms

(iii) 52 g of He

1 mole of He = 4 g = 6.022 × 10²³ atoms of He

52 grams of He will contain = 52/4 = 13 moles
Number of atoms in 13 moles of He = 13 × 6.022 × 10²³atoms
Number of atoms in 13 moles of He = 78.29× 10²³ atoms
52 grams of He = 7.829 × 10²⁴ atoms