1. Solutions

2. A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
12.1

3. Solutions Solvent: greater quantity (water)
Solute: smaller quantity (sugar)
Immiscible: two liquids do not mix
miscible: two liquids can mix
alcohol in water
(in any quantities)

4. Parts of a Solution
Solute
Solvent
Example
solid
liquid
gas

5. A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
12.1

6. Three types of interactions in the solution process:
solvent-solvent interaction
solute-solute interaction
solvent-solute interaction
DHsoln = DH1 + DH2 + DH3
12.2

7. “like dissolves like”
Two substances with similar intermolecular forces are likely to be soluble in each other.
non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
polar molecules are soluble in polar solvents
C2H5OH in H2O
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
12.2

8. Concentration Units Molarity (M) moles of solute M =
liters of solution
Molality (m)
m =
moles of solute
mass of solvent (kg)
12.3

9. Temperature and Solubility
Solid solubility and temperature
solubility decreases with increasing temperature
solubility increases with increasing temperature
12.4

10. Temperature and Solubility
Gas solubility and temperature
solubility usually decreases with increasing temperature
12.4

11. Pressure and Solutions
Henry’s law
P 
Solubility  (gas in liquid)

12. Pressure and Solubility of Gases
The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).
c is the concentration (M) of the dissolved gas
c = kP
P is the pressure of the gas over the solution
k is a constant (mol/L•atm) that depends only
on temperature
low P
high P
low c
high c
12.5

13. Calculating the solubility
If we want to make an accurate prediction about whether something will dissolve in water or not, we need to know four key factors:
1 the type of solute 3 the volume of solvent
2 the mass of solute 4 the temperature
We can say, for example, that the solubility of salt in water at 20 °C is 35 grams per 100 cm3 of water.
This means that at 20 °C you can completely dissolve 35g of salt in 100cm3 of water.
In general:  Solubility = mass of solute / volume of solvent

14. Solubility of potassium nitrate
How Much Will Dissolve?
The table shows how much potassium nitrate (a type of fertiliser) and potassium chloride (the main ingredient in ‘Lo-Salt’) dissolve in water at different temperatures. The numbers tell you how many grams of solute dissolve in 100 cm3 water.
Temperature (°C)
Solubility of potassium nitrate
Solubility of potassium chloride 10 20 32 30 35 44 36 40 60 38 50 78
100 42

15. Graph showing the solubility of potassium nitrate and potassium chloride.

16. Questions
How does the solubility of the substances change as the temperature changes?
Which substance is the most soluble at 10°C?
Which substance is the most soluble at 40°C?
Copy and complete this sentence: ‘As the temperature rises, the solubility …’
Which of the two solids dissolves best a at 10 °C b at 40 °C?
Use your graph to estimate the solubility of potassium chloride at 55 °C

17. Colloid versus solution
A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus solution
collodial particles are much larger than solute molecules
collodial suspension is not as homogeneous as a solution
12.8

18. Suspensions These are mixed, but not dissolved in each other
Will settle over time
Particles are small
Mayo