A solution containing 1.8g of a non-electrolyte (empirical formula CH2O) in 40g of water is observed to freeze at −0.465∘C. The molecular formula of the compound is:
(Kf of water =1.86kg K mol−1)
A
C2H4O2
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B
C3H6O3
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C
C4H8O4
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D
C6H12O6
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Solution
The correct option is DC6H12O6
We know, ΔTf=Kf×molality ΔTf=Depression of freezing point=−0.465∘C Kf=1.86 kg K mol−1
Empircal formula given = CH2O
Let, molecular formula = (CH2O)n
Empirical formula mass =30u
Molecular formula mass =180u ∴n=Molecular formula massEmpirical formula mass=18030=6
So, molecular formula = C6H12O6.