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ICSE Class 10 Chemistry Question 68 of 72

Mole Concept & Stoichiometry Miscellaneous Exercises — Question 68

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Question

Question 52(a-ii)

A compound made up of two elements X and Y has an empirical formula X2 Y. If the atomic weight of X is 10 and that of Y is 5 and the compound has a vapour density (V.D.) 25, find it's molecular formula.

Answer

Empirical formula is X2Y

Empirical formula weight = 2(10) + 5 = 25

Vapour density (V.D.) = 25

Molecular weight = 2 x V.D. = 2 x 25

n=Molecular weightEmpirical formula weight=2×2525=2\text{n} = \dfrac{\text{Molecular weight}}{\text{Empirical formula weight}} \\[0.5em] = \dfrac{2 \times 25}{25} = 2

∴ Molecular formula = n[E.F.] = 2[X2Y] = X4Y2