Find the molecular formula of alkene, the mass fraction of hydrogen, which is 14.3%

Find the molecular formula of alkene, the mass fraction of hydrogen, which is 14.3%. The relative density of this substance for hydrogen is 21.

Given:
ω (H in in-ve) = 14.3%
D H2 (in-va) = 21

To find:
in -?

Decision:
1) Mr (in-va) = M (in-va) = D H2 (in-va) * M (H2) = 21 * 2 = 42;
2) N (H in in-ve) = (ω (H in in-ve) * Mr (in-va)) / (Ar (H) * 100%) = (14.3% * 42) / (1 * 100%) = 6;
3) in-in – alkene – C (n) H (2n);
4) 2n = N (H in in-ve) = 6;
5) n = 6/2 = 3;
6) C3H6 – propene.

Answer: Unknown substance – C3H6 – propene.