Hydrocarbon contains 75% carbon 25% hydrogen Calculate the hydrocarbon formula.

Given:
CxHy
ω (C in CxHy) = 75%
ω (H in CxHy) = 25%

Find:
CxHy -?

Solution:
1) Let m (CxHy) = 100 g;
2) m (C in CxHy) = ω (C in CxHy) * m (CxHy) / 100% = 75% * 100/100% = 75 g;
3) n (C in CxHy) = m (C in CxHy) / M (C) = 75/12 = 6.25 mol;
4) m (H in CxHy) = ω (H in CxHy) * m (CxHy) / 100% = 25% * 100/100% = 25 g;
5) n (H in CxHy) = m (H in CxHy) / M (H) = 25/1 = 25 mol;
6) x: y = n (C in CxHy): n (H in CxHy) = 6.25: 25 = 1: 4;
7) Unknown substance – CH4 – methane.

Answer: Unknown substance – CH4 – methane.