Expressing Solubility

• Solubility of a solute can be expressed in terms of molarity, molality, and percent by weight.
• Molarity is the number of moles of solute contained in 1 liter of solution.
• Molality is the number of moles of solute dissolved in 1000 g of solvent.
• Percent by weight is the mass of solute per 100 g of solution.

Mole Fraction and Mole Percent

• Mole fraction (X) of a solute is the ratio of the number of moles of solute to the total number of moles of solute and solvent.
• Mole fraction of solute = No. of moles of solute / (No. of moles of solute + No. of moles of solvent)
• Mole percent of solute = X1 x 100
• Mole percent of solvent = X2 x 100

Normality

• Normality is the number of gram equivalents of solute per liter of solution.
• Gram equivalent mass = Molar mass / Equivalence factor

Solubility Calculations

• Problem 1: Molarity of a solution prepared by dissolving 75.5 g of KOH in 450 ml of solution.
• Problem 2: Weight of HCl present in 150 ml of a 0.5 molar solution.
• Problem 3: Molality of a solution made by dissolving 1.45 g of sucrose in 30 ml of water.
• Problem 4: Mole fraction of HCl of a solution containing 36% HCl by weight.

Semi-Polar Solvents

• Semi-polar solvents have strong dipoles but cannot break ionic or covalent bonds.
• Examples of semi-polar solvents: Ketones.
• They can increase the solubility of benzene in water and castor oil in water.

Concentration of a Solution

• Percent by weight: % = mass of solute / mass of solution x 100
• Percent by volume: % w/v = mass of solute / volume of solution x 100
• Percent volume by volume: % v/v = volume of solute / volume of solution x 100
• Parts per million (PPM): ratio of parts of solute per 1 million parts of the solution
• 1 PPM = 1 milligram / liter (mg/L) = 1 milligram / kilogram (mg/Kg)