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

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(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

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(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

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(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

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Answer 2

Explanation:

(i) 52 moles of Ar

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

mass of 1 atom of He = 4u

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

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

hope it helps