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Question
A compound with empirical formula AB2 has the vapour density equal to its empirical formula weight. Find its molecular formula.
Solution 1
Now since the empirical formula is equal to vapour density and we know that vapour density is half of the molecular mass i.e. we have n = 2 so, the molecular formula is A2B4.
Solution 2
Empirical formula of the given compound = AB2
As we know, Vapour density = Empirical formula weight
∴ Molecular weight = 2 x vapour density
n = `"Molecular weight"/"Empirical formula weight"`
= `(2 xx"vapour density")/"vapour density"`
= 2
∴ Molecular formula = A2B4
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