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प्रश्न
A solution containing 0.73 g of camphor (molar mass 152 g . mol-1) in 36.8 g of acetone (boiling point 56.3°C) boils at 56.55°C. A solution of 0.564 g of unknown compound in the same weight of acetone boils at 56.46oC. Calculate the molar mass of the unknown compound.
उत्तर
Calculation for Kb of camphor:
Here, mass of solvent, WA = 36.8g
mass of solute, WB = 0.73g
molecular mass of solute, MB = 152
elevation in boiling point,
ΔTb = 56.55 - 56.30 = 0.25°C
Now,
ΔTb = Kb × (WB × 1000)/(WA × MB)
Kb = (ΔTb × WA × MB)/(WB × 1000)
Kb = (0.25 × 36.8 × 152)/(0.73 × 1000)
Kb =1.9156 °C kgmol-1
Calculation of molecular mass of unknown solute
Here, mass of solvent, WA = 36.8g
mass of solute, WB = 0.564g
elevation in boiling point,
ΔTb = 56.46 - 56.30 = 0.16°C
Now,
Mb = (Kb × WB × 1000)/(WA × ΔTb)
Mb = (1.9156 × 0.564 × 1000)/(36.8 × 0.16)
Mb =183.4 g
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