The mass fractions of carbon and hydrogen in the hydrocarbon are 92.31% and 7.69%, respectively.

The mass fractions of carbon and hydrogen in the hydrocarbon are 92.31% and 7.69%, respectively. Give the molecular and structural formula of a given substance if it is known that one of its molecules contains six carbon atoms.

Given:
Hydrocarbon – C6Hx
ω (C in C6Hx) = 92.31%
ω (H in C6Hx) = 7.69%

To find:
C6Hx -?

Decision:
1) Calculate the relative molecular weight of C6Hx:
Mr (C6Hx) = N (C in C6Hx) * Ar (C) * 100% / ω (C in C6Hx) = 6 * 12 * 100% / 92.31% = 78;
2) Calculate the number of H atoms in C6Hx:
x = (ω (H in C6Hx) * Mr (C6Hx)) / (Ar (H) * 100%) = (7.69% * 78) / (1 * 100%) = 6;
3) Unknown hydrocarbon – C6H6 – benzene;

Answer: Unknown hydrocarbon – C6H6 – benzene.