Question

An element ₇A¹⁴ exists as diatomic gas in nature which is relatively inert and forms 78% of earth’s atmosphere. 

(a) Identify the gas and write its molecular formula. Write the formulae of its nitrite and nitrate ions. 

(b) How many moles of this gas would contain 12.044 × 10²³atoms of this element? (Avogadro’s no. = 6.022 × 10²³) 

(c) Calculate the molecular mass of 

(i) NH₄ NO₃ and                   (ii) HNO₃ 

(Given atomic masses N = 14 u, O = 16 u, H = 1u) 

Answer 1

(a) Element A has atomic number 7 so it is Nitrogen gas (N₂) 

Formulae: Nitrite ion (No₂ ⁻) 

Nitrate ion (No₃ ⁻) 

(b) 1 mole of N₂ gas = 6.022 × 10²³ molecules of N₂ 

= 12.044 × 10²³ atoms of N 

(c) (i) Molecular mass of NH₄ NO₃ 

= 14 + 1 × 4 + 14 + 3 × 16 

= 80 u 

(ii) Molecular mass of HNO₃ 

= 1 + 14 + 3 × 16 

= 63 u