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Question
A compound has the following percentage composition by mass: carbon 14.4%, hydrogen 1.2% and chlorine 84.5%. The relative molecular mass of this compound is 168, so what is its molecular formula?
Solution
Empirical formula mass = 12 × 1 + 1 × 1 + 35.5 × 2
= 12 + 1 + 71
= 84
Relative molecular mass (given) = 168
n = `"Relative molecular mass"/"Empirical formula mass"`
= `168/84`
n = 2
Molecular formula = (CHCl2)2
= C2H2Cl4
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