Question

Question 1.33 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.

Class XI Some Basic Concepts of Chemistry Page 25

Answer 1

(i) 1 mol of Ar = 6.022×1023atoms
∴ 52 mol of Ar = 52×6.022×1023atoms = 3.131×1025atoms

(ii) 1 atom of He = 4 u of He
4 u of He = 1 Atom of He
∴ 52 u of He = 1/4 × 52 = 13 atoms

(iii) 1 mol of He = 4 g = 6.022×1023atoms
∴ 52 g of He = (6.022×1023/4) × 52 atoms = 7.8286×1024atoms

Answer 2

(i) 52 moles of Ar

we know,
1 mole of Ar = 6.022 × 10²³ atoms
52 mole of Ar = 52 × 6.022 × 10²³ atoms
= 313.144 × 10²³ atoms
= 3.13144 × 10²⁵ atoms


(ii) 52u of He

we know,
mass of 1 atom of He = 4u
e.g., 4u of He = 1 He atom
∴ 1u of He = 1/4 He atom
∴ 52u of He = 52/4 He atoms = 13 He atoms

(iii) 52g of He

we know,
1 mole of He = 4g = 6.022 × 10²³ atoms of He
no of mole of He of 52g He = 52/4 = 13
∴ no of atoms in 13 mole of He = 13 × Avogadro's constant
= 13 × 6.022 × 10²³ atoms
= 78.286 × 10²³ atoms
= 7.8286 × 10²⁴ atoms