Question

Complete combustion of 0.858 g of compound X gives 2.63 g of CO₂ and 1.28 g of H₂O The lowest molecular weight X can have is

(a) 172

(b) 129

(c) 86

(d) 43

Answer 1

Correct option is (d) 43

Given,

molar mass of CO₂ ​= 2.630g or since the molar mass of CO₂ ​is 44g/mol

we have 0.05976 moles of CO₂ ​since there is 1 mole. so C in CO₂

we have 0.05976 moles of C or 0.718 g of C

mass of H₂O = 1.280 g or since the molar mass of water is 18 g/mol

we have 0.07105 mole of H₂O since there are 2 moles of H in 1 moles of H₂O = 0.14210 moles of H or 0.143 g of H molar ratio C : H = 0.05976 : 0.14210

mass of C + H = 0.861 g

or, after divinding by the smallest 0.05976

molar ratio of C : H = 1.000 : 2.378