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Solutions — Chemistry STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceChemistrySolutions5 Marks
Question
  1. Define the following terms:
  1. Mole fraction.
  2. Ideal solution.
  1. 15.0 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution freezes at - 0.34°C. What is the molar mass of the material?

(Kf for water = 1.86 K kg mol–1).

✓

Answer

  1.  
  1. The Ratio of number ofmoles of one component to the total number of moles of solution./ormathematical expression.
  2. The Solution which follows Raoult’s law over the entire range of concentrations.
  1.  WB = 15 g    WA = 450 g
    $\Delta$Tf = 0.34 oC    Kf = 1.86 Kkg/mol    MB = ?

$\text{M}_{B}=\frac{1000\times\text{K}_{f}\times\text{W}_{B}}{\Delta\text{T}_{f}\times\text{W}_{A}}$

$\text{M}_{B}=\frac{1000\times\text{1.86 k mol}^{-1}\times\text{15g}}{0.34\text{K}\times\text{450g}}$

= 182.35 g/mol.

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