Chem 112 Exam AID Course Pack

Chem 112 Exam AID Course Pack

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: kes the composition move towards a mixture with a lower boiling point) - maximum- boiling azeotropes can be purified by distillation since the lowest boiling point is actually the pure substance Colligative properties are properties which are dependent on the number of molecules of solute present in a solvent, but not on the type of molecules. - assumes that solutions are ideal and that the solute is non- volatile - colligative properties transpire because of the changes in entropy of the solution when we add a solvent to a solute. By doing so, the entropy increases and requires energy to reorder - (note that to make sure that enthalpy as close to zero as possible, we only generally consider solutions that are very dilute; accuracy decreases as concentration increases) Ethan Newton & Barry Zhang for SOS Winter 2012 25 - colligative properties include boiling point elevation, freezing point depression, vapour pressure lowering, and osmotic pressure don’t forget that ionic substances dissociate in solution; the number of particles includes all ions (so 0.1M NaCl dissociates to give 0.2M of particles) Vapour pressure lowering is the same idea as with the Raoult’s Law deviations above, except that only one of the substances is volatile. - the other substance is there, but is not contributing to the overall vapour pressure; and since it decreased the mole fraction of the substance that is volatile, the overall pressure lowers thus vapour pressure of the solution can be determined using the following relationship: - € * Psolution = Psolvent = χsolvent × Psolvent the amount of lowering obeys Raoult’s Law, since we assume ideal solutions for colligative properties Boiling point elevation - a direct consequence of vapour pressure lowering - a substance boils when its vapour pressure has risen high enough to equal atmospheric pressure - since the vapour pressure for any given temperature is lower, you will need a higher temperature to reach the same vapour pressure - on a phase diagram, the line between liquid and gas moves right - ΔTb = ikbm (boiling point elevation constant times molality times the electrolyte factor) - “i” is the number of ions an electrolyte dissociates into - in practice, “i” is normally slightly less than that, since there is some small f...
View Full Document

This note was uploaded on 10/02/2012 for the course CHEM 112 taught by Professor Carran during the Winter '08 term at Queens University.

Ask a homework question - tutors are online