CHEM 101
Introduction to Fundamental Chemistry
Spring Quarter 2008 SCCC
Lecture 34
http://seattlecentral.edu/faculty/lcwest/CHE101
Solutions and Colloids
ƒ Physical States of Solutions 9
ƒ Solubility9
ƒ The Solution Process 9
ƒ Solution Concentrations
ƒ Soultion Preparation
Please don’t leave studying for the midterm till the last minute. If
you have anything I can help you with please come see me.
Polar but non-ionic solutes dissolve in water via a similar
mechanism as for ionic compounds.
A solute will be insoluble in a solvent if:
1. Forces between solute particles are greater than the
forces between solute particles and the solvent.
A solute will be insoluble in a solvent if:
2. Forces between the solvent particles are stronger than
forces between the solvent and the solute.
e.g. The only attractive force between oil and water will is
dispersion forces. These are weak compared to hydrogen
bonds between water molecules.
In a polar solvent there will be
attraction between the
oppositely charged ends of the
molecule.
A good “rule of thumb” that works especially well for non-ionic
compounds is:
“Like dissolves like”
i.e. Polar solvents dissolve polar solutes well and non-polar
solvents dissolve non-polar solutes well.
There are some more specific rules that allows us to better
estimate the solubility of ionic compounds.
You will be given these if you need them.
The rate of dissolution is dependent upon:
1. The surface area of the solute.
i.e. how finely divided it is.
Increasing rate
The rate of dissolution is dependent upon:
2. How hot the solution is.
i.e. the kinetic energy of solute and solvent.
3. The rate of stirring.
Typically when we are
preparing a solution in
the lab we will both
heat and stir.
When a solute dissolves in a solvent heat can be released or
absorbed.
When heat is absorbed the process is endothermic and the
solution becomes cooler.
This effect is used in instant cold packs for sporting injuries and
first aid.
More commonly dissolution is an exothermic process and heat
is released when a solute is dissolved.
Sometimes when we make a solution it will get so hot it boils!!
What is the safest way to prepare a solution?
Read sections 7.5.-7.9
Study Examples
Prepare for midterm