On dissolving 3.24g of sulphur in 40g of benzene, the boiling point of the solution was higher than that of benzene by 0.81K. What is the molecular formula of sulphur? (Given, Kb for benzene =2.53Kkgmol−1, atomic mass of sulphur =32gmol−1)
A
S4
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B
S8
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C
S2
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D
S6
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Solution
The correct option is BS8 The given values are: weight of solute, WB=3.24g weight of solvent, WA=40g △Tb=0.81K;Kb=2.53Kkgmol−1 Using the formula, MB=Kb×1000×WB△Tb×WA we get, ∴MB=2.53×1000×3.240.81×40=253
Let the molecular formula of sulphur be Sx The atomic mass of sulphur =32 Molecular mass =32×x ∴32x=253 x=25332=7.91≈8 So, the molecular formula of sulphur =S8