Question

an aromatic hydrocarbon with empirical formula C5H4 on treatment with conc. H2SO4
gave a monosulphonic acid.0.104g of the acid required 10ml of N/20 NaOH for complete neutralisation. What is the molecular formula of the hydrocarbon?​

Answer 1

for complete neutralisation,

equivalents of acid = equivalents of base.

of basicity of acid × number of mole of acid = acidity of base × number of mole of base.

or, 1 × 0.104g/M = 1 × normality × volume in litre

or, 0.104/M = (10/1000)L × 1/20 N

or, 0.104/M = 1/2000

or, M = 0.104 × 2000 = 208g/mol

so, molecular mass of monosulphonic acid is 208g/mol.

empirical formula of monosulphonic acid = R-SO3

molecular mass = molecular mass of -R +(32 + 48)

208g /mol= x × (mass empirical formula of hydrogen, C5H4) + 80 g/mol

or, 208 - 80 = x × (12 × 5 + 4)

or, 128 = x × 64

or, x = 2

hence, molecular formula of hydrocarbon = 2× (C5H4) = $C_{10}H_8$