Question

A hydrocarbon contains 86% carbon. 448 ml of the hydrocarbon weighs 1.68 g at STP. Then the hydrocarbon is an

(a) alkane

(b) alkene

(c) alkyne

(d) arene

Answer 1

Correct option is (b) alkene

Given that hydrocarbon has 86% C content.

In 100 gm hydrocarbon, mass of carbon will be 100 × 86% = 86 gm.

Moles of C are calculated by -

n(C) = 86/12

n(C) = 7.166mol

In 100 gm hydrocarbon, mass of hydrogen will be 100 - 86 = 14 gm.

Moles of H are calculated as -

n(H) = 14/1

n(H) = 14mol

Thus, C:H ratio will be 7.166:14 ≈ 1:2 which gives rise to empirical formula CH₂​.

Thus, given compound with molecular formula C_n​H_2n​ must be an alkene.