PROPERTIES OF SOLUTIONS [PROBLEMS ONLY]
Units of solution concentration
➢ Molarity (M) = # of moles of solute per liter of solution
▪ Mass percent (weight percent) = percent by mass of the solute in the solution
➢ Mole fraction (() = ratio of the number of moles of a given component to the total number of moles of solution.
Mole fractiona = (a [pic]
➢ Molality (m) = # of moles of solute per kilogram of solvent
NOT temperature dependent.
Represents a ratio of solute:solvent molecules at all times.
Exercise 1 Various Methods for Describing Solution Composition
Exercise 4 Calculations Using Henry’s Law
A certain soft drink is bottled so that a bottle at 25°C contains CO2 gas at a pressure of 5.0 atm over the liquid. Assuming that the partial pressure of CO2 in the atmosphere is 4.0 X 10-4 atm, calculate the equilibrium concentrations of CO2 in the soda both before and after the bottle is opened. The Henry’s law constant for CO2 in aqueous solution is 32 L • atm/mol at 25°C.
Psolution = ((solvent) (Posolvent)
▪ Psolution = observed vapor pressure of the solvent in the solution
▪ (solvent = mole fraction of solvent
▪ Posolvent = vapor pressure of the pure solvent
▪ i = van’t Hoff factor (moles of electrolyte must be multiplied by this)
Exercise 5 Calculating the Vapor Pressure of a Solution
Calculate the expected vapor pressure at 25°C for a solution prepared by dissolving 158.0 g of common table sugar (sucrose, molar mass = 342.3 g/mol) in 643.5 cm3 of water. At 25°C, the density of water is 0.9971 g/cm3 and the vapor pressure is 23.76 torr.
Exercise 6 Calculating the Vapor Pressure of a Solution
Containing Ionic Solute
Predict the vapor pressure of a solution prepared by mixing 35.0 g solid Na2SO4 (molar mass = 142 g/mol) with 175 g water at 25°C. The vapor pressure of pure water at 25°C is 23.76 torr.
Exercise 7 Calculating the Vapor Pressure a Solution Containing Two Liquids
A solution is prepared by mixing 5.81 g acetone (C3H6O, molar mass = 58.1 g/mol) and 11.9 g chloroform (HCCl3, molar mass = 119.4 g/mol). At 35°C, this solution has a total vapor pressure of 260. torr. Is this an ideal solution? The vapor pressures of pure acetone and pure chloroform at 35°C are 345 and 293 torr, respectively.