Find the molecular formula for a hydrocarbon containing 75% carbon and 25% Hydrogen.

| April 9, 2021 | education

Find the molecular formula for a hydrocarbon containing 75% carbon and 25% Hydrogen. The relative density of this substance in the air is 0.55.

Let’s implement the solution according to the plan:
1. Determine the molar mass of the hydrocarbon by the formula:
M (CxHy) = M (air) * D (air) = 29 * 0.55 = 15.95 g / mol;
2. Let’s calculate the number of moles of carbon, hydrogen according to the formula:
Y (C) = m / M = 75/12 = 6.25 mol;
Y (H) = m / M = 25/1 = 25 mol;
3. Ratio. C: H = 6.25: 20 = 1: 3, hence the simplest formula: CH3;
4. General formula of hydrocarbon: СnH2n.
5. Find the value –n
6.12n + 2 = 16;
n = 1;
7. The molecular formula of the hydrocarbon is CH4, M (CH4) = 12 + 4 = 16 g / mol;
Answer: the hydrocarbon has the molecular formula CH4 – methane.



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