The hydrocarbon contains 85.71% carbon by weight. Set its molecular weight and structural formula

The hydrocarbon contains 85.71% carbon by weight. Set its molecular weight and structural formula if the relative density of this hydrocarbon in air is 2.41.

Given:
CxHy
ω (C in CxHy) = 85.71%
D air. (CxHy) = 2.41

To find:
Mr (CxHy) -?
CxHy -?

Decision:
1) M (CxHy) = D air. (CxHy) * M (air) = 2.41 * 29 = 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; the relative molecular weight is 70.