8.5: Solubility and Saturation
Solubility
• The maximum mass of solute that can be dissolved per
100 mL (or g) of water at a given temperature.
• For example, the solubility of sucrose is
204.0g/100g H2O, which means that up to 204.0 g of
sucrose can dissolve in 100 mL of water.
Any excess amount will not dissolve!
EXAMPLE
NaCl in water is 35.9g/100mL at 20oC
O2(g) in water is 0.0009g/100mL at 20oC
Which is more soluble?
Difference Between Soluble, Sparingly
Soluble and Insoluble
Soluble
more than 1g of solute will dissolve in 100mL of solvent
Sparingly Soluble
0.1g – 1g of solute will dissolve in 100mL of solvent
Insoluble
less than 0.1g of solute will dissolve in 100mL of solvent
Solubility
• Saturated Solution – a solution that contains the
MAXIMUM quantity of solute (at a given temperature
and pressure)
• Unsaturated Solution – a solution that contains LESS
than the maximum quantity of solute (at a given
temperature and pressure)
• Supersaturated Solution – a solution that contains
MORE than the maximum quantity of solute (at a given
temperature and pressure). Are unstable!
Solubility
• How can you tell what kind of solution you have?
• Add more solute!
• If it dissolves, solution is UNSATURATED
• If it does not dissolve, solution is SATURATED
• If a weird, unexpected reaction happens, it is
SUPERSATURATED!
Solubility Curves
• a graph of the solubility of a substance over a range of
temperatures
• Ex:
•
•
•
•
At 30ºC, the solubility of sucrose is
220g/100g H2O
What is the solubility of sucrose at 60oC?
What happens to the solubility as temperature increases?
Solubility Curves
• Points ON the curve represent a saturated solution
• Points BELOW the curve represent an unsaturated
solution
• Points ABOVE the curve represent a supersaturated
solution
Solubility Curves of Ionic
Compounds
• Generally, solubility of ionic compounds increases as
temperature increases. However, they are affected by
temperature differently.
Example: A potassium sulfate solution, K2SO4(aq), containing 11.8
g/100 g H2O at 20oC, is warmed to 60OC. What additional mass of
potassium sulfate is required to saturate this solution at 60OC?
• Step 1: Find the data point on the graph. Is the solution
unsaturated, saturated, or supersaturated?
• Step 2: Determine the difference between this point and
the curve.
Solubility Curves of Gases
• The solubility of gases decreases as the temperature
increases
• At 0oC, water can hold about twice as much oxygen
(0.0140g/L H2O) than water at 35oC (0.0070g/L H2O)
• This shows that cool water contains more dissolved oxygen
than warmer water. How does this affect aquatic animals?
How does Pressure affect
Solubility?
• Pressure does not have much effect on solids and liquids
because these states are not very compressible.
• Pressure has a large effect on gases. Solubility of a gas
increases as pressure increases.
8.5: pg 397 # 1, 3, 4, 6, 8, 9