A hydrocarbon was analyzed and found to contain 85.7\% carbon and 14.3\% hydrogen by mass.… — JAMB UTME

A hydrocarbon was analyzed and found to contain $85.7\%$ carbon and $14.3\%$ hydrogen by mass. What is the empirical formula of the hydrocarbon? [Relative atomic masses: $\text{C} = 12$ , $\text{H} = 1$ ]

Answer: CH2 / CH_2 / CH₂

Answer

CH₂

By dividing the mass percentage of each element by its relative atomic mass (Carbon:

85.7/12 = 7.142

, Hydrogen:

14.3/1 = 14.3

), the mole ratio obtained is

1:2

after dividing by the smallest value (

7.142

). Hence, the empirical formula is

\text{CH}_2

Step-by-Step Solution

Calculate the mole ratio of each element by dividing their mass percentages by their respective relative atomic masses.

Moles of Carbon =

\frac{85.7}{12} = 7.142\text{ mol}

; Moles of Hydrogen =

\frac{14.3}{1} = 14.3\text{ mol}

Molar mass converts mass percentages into relative molar quantities.

Divide each mole value by the smallest number of moles to obtain the simplest whole-number ratio.

Carbon ratio =

\frac{7.142}{7.142} = 1

; Hydrogen ratio =

\frac{14.3}{7.142} = 2

Empirical formula represents the simplest whole-number ratio of atoms in a compound.

Write the chemical formula using the calculated whole-number ratio.

Empirical Formula =

\text{CH}_2

Combining the simplest ratio yields 1 atom of C for every 2 atoms of H.

Key Concept

Empirical Formula Calculation from Percentage Composition

Estimated Time:1m 30s

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