Question

36. The general formula of carbohydrate is Cx (H2O)y 3.1 g of carbohydrate on heating in absence of
oxygen yield 1.24 g of carbon. The molecular formula of carbohydrate is 180u. Calculate its
molecular formula.
yoen to form sulphur dioxide
10​

Answer 1

Answer:

The carbohydrate may be regarded as the hydrate of carbon

Percentage of carbon (C) in carbohydrate =(1.24g)(3.10g)×100=40

Percentage of water (H2O) in carbohydrate =100−40=60

Moles of C=(40g)(12 g mol−1)=3.33 mol

Moles of H2O=(60g)(18 g mol−1)=3.33 mol

∴ Mole ratio of C:H2O::1:1

Empirical formula of carbohydrate =C(H2O)

Empirical formula mass =12+18=30 u

Molecular mass = 180u (given) , n=Molecular massEmpirical formula mass=(180 u)(30 u)=6

∴ Molecular formula of carbohydrate =6×(CH2O)=C6H12O6.