The vapour pressure of 0.1M KNO, at 100 °C is 730 Torr. The activity of water in the solution at this temperature is: 

CONCEPT:

Vapour Pressure and Activity of Solvent

• The activity of a solvent in a solution is related to its vapor pressure. It can be calculated using Raoult's Law, which states:

  P_solution = a_solvent × P_{pure solvent}

• Here:
  • P_solution = Vapor pressure of the solution
  • P_{pure solvent} = Vapor pressure of the pure solvent
  • a_solvent = Activity of the solvent in the solution
• The activity of the solvent (a_solvent) can be calculated as:

  a_solvent = P_solution / P_{pure solvent}

EXPLANATION:

• In the given problem:
  • P_solution = 730 Torr
  • P_{pure solvent} = 760 Torr (vapor pressure of pure water at 100 °C)
• Using the formula for activity:

  a_solvent = P_solution / P_{pure solvent}

  • a_solvent = 730 / 760
  • a_solvent = 0.96

Therefore, the activity of water in the solution at 100 °C is 0.96.