A 0.2 percent aqueous solution of a non-volatile solute exerts a vapour pressure of 1.004 bar at 100°C. What is the molar mass of the solute? (Given: vapour pressure of pure water at 100°C is 1.013 bar and molar mass of water is 18 g mol)
Answer: M ≈ 4.1 g mol⁻¹ (*)
Solution
0.2% solution: 0.2 g solute in 100 g solution, i.e. in 99.8 g water.
Relative lowering:
Moles of water:
For a dilute solution, :
Molar mass:
(*) The printed data force this physically odd value; the method above is the intended one.
Relative lowering:
Moles of water:
For a dilute solution, :
Molar mass:
(*) The printed data force this physically odd value; the method above is the intended one.
CBSE Class 12 Board · 2006 · Delhi Compartment · Subjective