Question

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

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

(c) Define the term molecular mass.

(d) Determine the molecular mass of ZnSO4.

[Atomic mass of Zn = 65 u, * = 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