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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. Van’t Hoff factor.
  1. 100 mg of a protein is dissolved in enough water to make 10.0 mL of a solution. If this solution has an osmotic pressure of 13.3 mm Hg at 25° C, what is the molar mass of protein?

(R = 0.0821 L atm mol–1 K–1 and 760 mm Hg = 1 atm.)

✓

Answer

  1.  
  1. Mole fraction is the ratio of number of moles of one component to the total number of moles in a mixture.
  2. Van't Hoff factor is expressed as:

$\text{i}=\frac{\text{norml molar mass (m}_{1})}{\text{abnormal molar mass (m'}_{1})\text{(due to dissociation or association )}}$

  1. $\pi$ = CRT

$\text{M}_{2}=\frac{\text{w2RT}}{\pi\text{ V}}$

$\text{M}_{2}=\frac{100\times10^{-3}\text{g}\times0.0821\text{ L atm mol}^{-1}\text{K}^{-1}\times\text{298 K}\times760\times1000}{\text{13.3 atm}\times\text{10L}}$

M2 = 13980g mol–1 or 1.4 x 104g mol–1.

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