Calculate the percentage by weight of :

(a) C in carbon dioxide

(b) Na in sodium carbonate

(c) Al in aluminium nitride.

[C = 12, O = 16, H = 1, Na = 23, Al = 27, N = 14]

(a) Molecular weight of carbon dioxide CO₂ = 12 + (2 x 16) = 12 + 32 = 44

44 g of CO₂ contains 12 g of carbon

∴ 100 g of CO₂ contains $\dfrac{12}{44}$ x 100 = 27.27% of carbon

Hence, percentage by weight of C in CO₂ is 27.3%

(b) Molecular weight of sodium carbonate Na₂CO₃ = (2 x 23) + 12 + (3 x 16) = 46 + 12 + 48 = 106

106 g of sodium carbonate Na₂CO₃ contains 46 g of sodium

∴ 100 g of Na₂CO₃ contains $\dfrac{46}{106}$ x 100 = 43.39% ≈ 43.4% of sodium.

Hence, percentage by weight of sodium in sodium carbonate is 43.4%

(c) Molecular weight of Aluminium Nitride = AlN = 27 + 14 = 41

41 g of Aluminium Nitride contains 27 g of Aluminium

∴ 100 g of Aluminium Nitride contains $\dfrac{27}{41}$ x 100 = 65.85% of Aluminium

Hence, percentage by weight of Aluminium in Aluminium Nitride is 65.85%