The relative density (D) for hydrogen is 8. Determine the alkane formula.

The molecular weight of hydrogen is 2 g / mol. Let’s find the molecular weight of the unknown alkane:
8 * 2 = 16 g / mol;

The general formula for alkanes looks like this: CnH2n + 2. The relative atomic mass of carbon is 12, hydrogen is 1. According to the condition of the problem, an equation was drawn up:
12n + 2n + 2 = 16;

12n + 2n = 16 – 2;

14n = 14;

n = 14/14;

n = 1;

If n = 1, then 2n + 2 = 2 * 1 + 2 = 4;

Answer: the alkane formula is CH4 (methane).