Question

Calculate the number of atoms in each of the following:

1. 52 moles of Ar
2. 52 u of He
3. 52 g of He.

Answer 1

Given:

Avogadro’s number, N_A = 6.022 × 10²³ mol⁻¹
Atomic mass of He = 4 u
Molar mass of He = 4 g mol⁻¹

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(i) Number of atoms in 52 moles of Ar

Number of atoms = Moles × Avogadro’s number

= 52 × 6.022 × 10²³

= 3.13 × 10²⁵ atoms

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(ii) Number of atoms in 52 u of He

Atomic mass of one He atom = 4 u

Number of atoms = Total mass / Mass of one atom

= 52 / 4

= 13 atoms

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(iii) Number of atoms in 52 g of He

Number of moles of He = Mass / Molar mass

= 52 / 4 = 13 mol

Number of atoms = 13 × 6.022 × 10²³

= 7.83 × 10²⁴ atoms

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Final Answers:

(i) 52 moles of Ar = 3.13 × 10²⁵ atoms
(ii) 52 u of He = 13 atoms
(iii) 52 g of He = 7.83 × 10²⁴ atoms