2. Hydrocarbons consist of carbon and hydrogen. 5.7 g of a hydrocarbon contains 4.8 g of carbon. If the relative molecular mass of the hydrocarbon is 114, determine its molecular formula.​

The molecular formula of the hydrocarbon compound is C₈H₁₈

Explanation:

The type of chemical substance in the question = Hydrocarbon

The mass of the hydrocarbon = 5.7 g

The mass of carbon in the given hydrocarbon (sample) = 4.8 g

The relative molecular mas of the hydrocarbon = 114 g

Therefore, the mass of hydrogen in the sample, H = 5.7 g - 4.8 g = 0.9 g

The ratio of the mass of carbon in the sample = 4.8/5.7

The ratio of the mass of hydrogen in the sample = 0.9/5.7

By the law of constant composition, we have;

The mass of carbon in a mole of the hydrocarbon = (4.8/5.7) × 114 g = 96 g

The molar mass of carbon, C = 12 g/mol

The number of moles of carbon in a mole of the hydrocarbon, 'n₁', is given as follows;

n₁ = 96 g/12 g = 8 moles

The mass of hydrogen in a mole of the hydrocarbon = (0.9/5.7) × 114 g = 18 g

The molar mass of hydrogen, H ≈ 1 g/mol

The number of moles of hydrogen in a mole of the hydrocarbon, 'n₂', is given as follows;

n₂ = 48 g/1 g = 18 moles

Therefore, in each each molecule of the compound, we have have 8 atoms of carbon, 'C', and 18 atoms of hydrogen, 'H'

Therefore, we get;

The molecular formula of the hydrocarbon compound is C₈H₁₈ which is the chemical formula for the hydrocarbon also known as octane

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