1. The amount of solute that dissolves can vary
SECTION 4.2

2. Low concentration: low amounts of dissolved solute
A solution’s concentration depends on the amount of solute dissolved in a solvent at a particular temperature
Low concentration: low amounts of dissolved solute
High concentration: high amounts of dissolved solute

3. Degrees of concentration
Dilute Solution: a solution that has a low concentration of solute
Adding more solvent can dilute a solution (i.e. adding more water into a solution of salt water)
Concentrated Solution: a solution that has a high concentration of solute
Adding more solute raises the concentration of the solution
Saturated Solution: a solution that contains the maximum amount of solute that can be dissolved in the solvent at a given temperature

4. Supersaturated solutions
Sometimes, a solution contains more dissolved solute than is normally possible.
Supersaturated Solution
A saturated solution can become supersaturated if more solute is added while the temperature is raised

5. solubility
Solubility: the amount of that substance that will dissolve in a certain amount of solvent at a given temperature
Ex: a large amount of ammonia can dissolve in water (high solubility)
Ex: only a small amount of carbon dioxide can dissolve in water (low solubility in water)
Ex: Oils do not dissolve at all (insoluble)
The amount of solute needed to make a saturated solution depends on the solubility of a solute in a particular solvent.

6. Solubility can change: Temperature
Temperature increasing with a solid solute:
Solute dissolves more quickly
A greater amount of solute dissolves in the solvent
Temperature increasing with a gaseous solute:
Gas is less soluble in water

7. Solubility can change: pressure
Pressure does not have an effect on
a solid solute’s solubility.
The solubility of a gas:
Increases at higher pressures
Decreases at lower pressures

8. Temperature and pressure effects on solubility
Solute
Increased Temperature
Decreased Temperature
Increased Pressure
Decreased Pressure
Solid
Increase in solubility; faster dissolving
Decrease in solubility; slower dissolving
No effect on solubility
Gas
Decrease in solubility
Increase in solubility

9. Solubility depends on molecular structure
Water is polar, oil is nonpolar: their molecules are not attracted to each other
“Like dissolves Like”
Polar solvents (water) will dissolve polar solutes (sugar and salt)
Nonpolar solvents will dissolve nonpolar solutes (gasoline mixtures)