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For dilute solutions n2 << n1 , hence ignoring n2 in the denominator we get
w1 and M1 = Masses and molar masses of solvent .
w2 and M2 = Masses and molar masses of solute . Elevation of boiling point o o
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Increase in temperature increases the vapour pressure of a
A liquid boils at a temperature where the vapour pressure is equal to the atmospheric
Vapour pressure of the solvent decreases in the presence of nonvolatile solute .
The boiling point of a solution is always higher than that of the boiling point of the pure solvent in which the solution is prepared as .
The elevation of boiling point also depends on the number of solute molecules rather than their nature .
The increase in the boiling point = ΔTb = Tb – Tb 0 . This is known as elevation of boiling point .
Tb 0 = boiling point of pure solvent
Tb 0 = boiling point of solution
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In dilute solutions the elevation of boiling point Tb is directly proportional to the molal concentration of the solute in a solution . Mathematically ,
ΔTb ∝ m ΔTb = kb m m = Molality = number of moles of solute dissolved in 1 kg of solvent
Kb = constant of proportionality . It is also known as Boiling Point Elevation Constant or Molal Elevation Constant ( Ebullioscopy Constant ). The unit of Kb is K kg mol -1 .