Here's a problem:?

Question

A hydrocarbon contains 85.7% C and the rest H. If the

molecular weight of the 42.06 g/mol, determine its molecular

formula.

Use these masses: C = 12.01 g/mol, H = 1.01 g/mol

I think the compound is propane. Am I correct?

Answer 1

Almost right...correct answer is cyclopropane or propene

You obv figured out that the C:H ratio is 1:2, giving an empirical formula of (CH2)...three of these gives MW of 42. But the only way that can occur is if all three C's are linked in a cyclic compound (cyclopropane) or if unsaturation is present (propene).

Added later:  A simple bromine test would distinguish between these...Br adds across propene's double bond.

Answer 2

Propane = 44.  Propene = 42.