Question

Calculate number of atoms is each of the following. (Average atomic mass : N = 14 u, S = 32 u)

a. 0.4 mole of nitrogen 

b. 1.6 g of sulfur

Answer 1

(a). 0.4 mole of nitrogen (N)

Number of atoms of N = Number of moles × Avogadro’s constant

= 0.4 mol × 6.022 × 10²³ atoms/mol

= 2.4088 × 10²³ atoms of N

(b). 1.6 g of Sulphur (S) 

Molar mass of sulphur = 32 g mol^-1

Number of moles = \(\frac{Mass\,of\,a\,substance}{Molar\,mass\,of\,a\,substance}\)

= \(\frac{1.6\,g}{32\,g\,mol^{-1}}\)

= 0.05 mol

Number of atoms of S = Number of moles × Avogadro’s constant

= 0.05 mol × 6.022 × 10²³ atoms/mol 

= 0.3011 × 10²³ atoms

= 3.011 × 10²² atoms of S

∴ (a) Number of nitrogen atoms in 0.4 mole = 2.4088 × 10²³ atoms of N

(b) Number of sulphur atoms in 1.6 g = 3.011 × 10²² atoms of S