Derive the formula of a substance, the mass fraction (in%) of carbon in which is 82.75, and hydrogen is 17.24. Vapor density in air 2.

1) Let the mass CxHy = 100 g. Then the mass of carbon = 82.75 g, and the mass of hydrogen = 17.24 g.
2) Find the amount of carbon substance:
82.75 / 12 = 6.9 mol
Now let’s find the amount of hydrogen substance:
17.24 / 1 = 17.24 mol
3) Let’s make the proportion
6.9 / 17.24 = 1 / 2.5 = 2/5
С2Н5 – the simplest
4) D = M (CxNu) / M air
2 = x / 29 (value 29 you need to know)
x = 58 g / mol
5) M C2H5 = 2 * 12 + 5 * 1 = 29
58/29 = 2
Multiply by 2
С4Н10 – molecular (butane)
Answer: С4Н10.