CHEM1312H - Intro to Colligative Properties

colligative properties

physical properties of solutions that depend on the number of solute particles (concentration measured as moles)

4 colligative properties to know

-vapor pressure lowering

-boiling point elevation

-freezing point depression

-osmotic pressure

van’t hoff factor definition

-the number of fragments a solute breaks up into for a particular solvent

-ex: when 1 mol of a non-electrolyte dissolves in water, it forms 1 mol of dissolved particles, but when 1 mol of an electrolyte dissolves in water, it normally forms more than 1 mol of dissolved particles (look at examples on slides)

van’t hoff factor

-used to measure the colligative properties of electrolyte vs non-electrolyte solutions

-previous assumption that the van’t hoff factor is equal to the number of ions per formula unit of the electrolyte

-the true (measured) value is given by the ratio of the measured value of a colligative property to the value calculated when the substance is assumed to be a non-electrolyte

-i = measured experimental value/expected calculated value

measured and theoretical i values

-the measured van’t hoff factors are generally less than the theoretical values due to pairing of ions in solutions

-the more concentrated the solution, the less the value of i is closer to the theoretical value

-the higher the charges on the ions, the less the value of i is closer to the theoretical value