Question

vapour pressure of 2% of an aqueous solution of a non volatile substance at 373k is 755mm.calculate the molecular weight of the solute.vapour pressure of pure water at 373k is760mm​

Answer 1

Answer:

Explanation:

Answer Text

Answer :

58.3 g mol−1

Solution :

P∘A−PSPS=xA

P∘A=760 mm hg, PS=755 mm Hg  

xB=P∘A−PSPS=760 mm Hg −755 mm Hg 755mmhg=0.0066

A 2.1% awueous solution means 2.1 g of solute in 100 g of solution

∴Mass of solvent =100g−2.1g=97.9g

∴Mass of solvent=100g2.1g−2.1g=97.9g

Moles of solvent nA=97.9g18 g mol−1=5.439g

xB=nBnA+nB or 1xB=nA+nBnB=nAnB+1

nAnB+1xB−1=10.0066−1=151.5−1=150.5

nB=nA150.5=(5.349mol)150.5=0.036mol.

Molar mass of folute=Mass of soluteMoles of solute=(2.1g)(0.036mol)=58.3 g mol−