10.5 g of ethylene hydrocarbon, formed by heating some alcohol

10.5 g of ethylene hydrocarbon, formed by heating some alcohol with sulfuric acid, added 40 g of bromine. What alcohol was the starting material?

General formula of ethylene hydrocarbons: CxH2x.

General formula of alcohols: CxH2x + 2O.

Let’s write down the equations of the ongoing reactions:

CxH2x + 2O = CxH2x + H2O (in sulfuric acid)

CxH2x + Br2 = CxH2xBr2

Let’s find the number of moles of Br2:

n (Br2) = m / M = 40/160 = 0.25 mol

n (Br2) = n (CxH2x) = 0.25 mol

M (CxH2x) = 12x + 2x = m / n = 10.5 / 0.25 = 42

14x = 42

x = 3 (number of carbon atoms)

Unsaturated hydrocarbon formula: C3H6 – propene.

The formula of the starting alcohol: C3H7OH – propanol.