Write the empirical formula of a compound that contains 60 % carbon and 40 % hydrogen by mass.

medium 2 marks Class 9 · Science · Atoms and Molecules

Answer

The correct answer is CH — Thus the empirical formula is ( $C_{1} H_{8}$ ). But check the numbers: 60 % C, 40 % H gives ratio 1 : 8. The simplest whole‑number ratio is (C H) after canceling? Wait, 1 : 8 is already whole numbers. However, typical empirical formula would be (C H_8). The question expects the simplest ratio of atoms, which is 1:8, so (C H_8).

Step-by-step solution

Assume a 100 g sample. Carbon mass = 60 g, Hydrogen mass = 40 g.
Convert masses to moles: - Carbon: (60/12 = 5) moles. - Hydrogen: (40/1 = 40) moles.
Divide each mole number by the smallest (5) to get the simplest whole‑number ratio: - Carbon: (5/5 = 1). - Hydrogen: (40/5 = 8).
Thus the empirical formula is ( $C_{1} H_{8}$ ). But check the numbers: 60 % C, 40 % H gives ratio 1 : 8. The simplest whole‑number ratio is (C H) after canceling? Wait, 1 : 8 is already whole numbers. However, typical empirical formula would be (C H_8). The question expects the simplest ratio of atoms, which is 1:8, so (C H_8).

Common mistake: Dividing by wrong smallest value or forgetting to reduce ratio

Concept tested: Empirical formula calculation

Published 13 October 2026 · How this solution was prepared and checked

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