Question

The vapour pressure of a solution of a non-volatile electrolyte B in a solvent Ais 95% of the vapour
pressure of the solvent at the same temperature. If the molecular weight of the solvent is 0.3 times the
molecular weight of solute, the weight of solute, the weight ratio of the solvent and solute are:​

Answer 1

HEY

↪ ACTUALLY WELCOME TO THE CONCEPT OF MOLE CALCULATION

We know ,

relative lowering of vapor pressure is the ratio of mole of solute to the mole of solvent.

e.g.,

Or, ∆P/P₀ = wM/Wm

Where w is the weight of solute

M is the molecular weight of solvent

W is the weight of solute

m is the molecular weight of solute

∆P is the lowering of vapor pressure

And P₀ is the initial vapor pressure

Given,

MB = 0.3MA

Let the intial vapor pressure ,P₀ = 100 Pa

Then, lowering of vapor pressure ,∆P = (100 - 95) Pa = 5 Pa

now,

5/100 = w × 0.3MA/W × MA

⇒1/20 = 0.3w/W

⇒w/W = 1/6

Hence , weight ratio of solute and solvent is 1/6