Question

(a) Calculate the number of moles in 112 g of iron. 

(b) Calculate the mass of 0.5 moles of sugar (C₁₂H₂₂O₁₁). 

(c) Define the term molecular mass. 

(d) Determine the molecular mass of ZnSO₄. 

[Atomic mass of Zn = 65 u, S = 32 u, O = 16 u] 

(e) Calculate the number of molecules of carbon dioxide, present in 4.4 g of CO₂. 

[Atomic mass of C = 12 u, O = 16 u, NA = 6.022 × 1023 mol⁻¹

Answer 1

(a) 1 mole of iron (Fe) = 56 g (molar mass) 

Since 56 g of iron = 1 mol 

Therefore, 112 g of iron= 1/ 56 ×112 mol = 2 mol 

(b) Molar mass of C₁₂H₂₂O₁₁ = (12 × 12) + (22 × 1) + (11 × 16) = 342 g 

Since mass of 1 mole of sugar = 342 g of sugar 

Therefore mass of 0.5 mole of sugar = 342 × 0.5 = 171 g 

(c) Molecular mass: Molecular mass is the sum of the atomic masses of all the atoms in a molecule of that substance. 

(d) Molecular mass of ZnSO₄ = (1 × 65) + (1 × 32) +(4 ×16) = 161 g 

(e) Molecular mass of CO₂ = 12 + 2 × 16 = 44 g 

Since 44 g of CO₂ contains 6.022 × 10²³ molecules 

Therefore, 4.4 g of CO₂ contains = 6.022×10²³ /44 ×4.4 = 6.022 × 10²²molecules