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Question
Complete the following calculations. Show working for complete credit :
If the empirical formula of a compound is CH and it has a vapour density of 13, find the molecular formula of the compound.
Solution
For acetylene , molecular mass = 2 X V.D. = 2 x 13 = 26g
The empirical mass = 12 (c) + 1(H) = 13g
n = `"Molecular formula mass"/"Empirical formula weight"`
= `26/13` = 2
Molecular formula of acetylene = 2 x Empirical formula =C2H2
Similarly, for benzene molecular mass = 2 X V.D = 2 x 39 = 78
n = 78/13 = 6
So, the molecular formula = C6H6.
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