# What is the molecular formula of a hydrocarbon containing 80% carbon.

What is the molecular formula of a hydrocarbon containing 80% carbon. The relative density of the vapors of this substance in the air is 1.035.

Let’s write down the condition of the problem:
Given: CxNu – hydrocarbon;
W (C) = 80%;
D (air) = 1.035;
M (air) = 29 g / mol;
M (C) = 12 g / mol;
Determine: molecular formula.
Decision:
M (CxHy) = M (air) * D (air) = 29 * 1.035 = 30 g / mol;
Let’s determine the amount of moles of carbon, hydrogen:
Y (C) = 80/12 = 6.6 mol;
m (C) = 30 * 0.80 = 24 g;
m (H) = 30-24 = 6 g;
Y (H) = m / M = 6/1 = 6 mol;
The ratio X: y = C: H = 6: 6 = 1: 1;
The simplest formula is CH;
Here is the general formula for the hydrocarbon: СnH2n + 2;
Find the value – n
CnH2n + 2 = 30;
12n + 2 + 2 = 30;
12n = 26;
n = 2;
Let’s derive the molecular formula: C2H6 (ethane);
M (C2H6) = 2 * 12 + 1 * 6 = 30 g / mol;
Answer: C2H6 is a saturated hydrocarbon, ethane.

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