Hydrocarbon contains 85.71% carbon, and its vapor density for hydrogen is 35. Determine the molecular formula

Given:
CxHy
ω (C in CxHy) = 85.71%
D H2 (CxHy) = 35

To find:
CxHy -?

Solution:
1) M (CxHy) = D H2 (CxHy) * M (H2) = 35 * 2 = 70 g / mol;
2) Mr (CxHy) = M (CxHy) = 70;
3) N (C in CxHy) = (ω (C in CxHy) * Mr (CxHy)) / (Ar (C) * 100%) = (85.71% * 70) / (12 * 100%) = 5 ;
4) ω (H in CxHy) = 100% – ω (C in CxHy) = 100% – 85.71% = 14.29%;
5) N (H in CxHy) = (ω (H in CxHy) * Mr (CxHy)) / (Ar (H) * 100%) = (14.29% * 70) / (1 * 100%) = 10 ;
6) Unknown substance – C5H10 – pentene.

Answer: Unknown substance – C5H10 – pentene.