Solubility
Section 8.5
Solubility

When we dissolve a solute in water, there is a point
where no more will dissolve

Saturated solution - a solution containing the
maximum quantity of a solute at specific temperature
and pressure conditions


look for the presence of undissolved solids in the solution
Solubility – the concentration of a saturated solution
of a solute at a specific temperature and pressure

Units for solubility are usually grams of solute per 100 mL
of solvent (g/100mL)
Other Important Terms

Unsaturated solution = a solution
containing less than maximum quantity of a
solute at specific temperature and pressure
conditions

Supersaturated solution = a solution that
contains more of the dissolved material than
could be dissolved by the solvent under
normal circumstances
Solubility
UNSATURATED
SOLUTION
more solute
dissolves
SATURATED
SOLUTION
no more solute
dissolves
SUPERSATURATED
SOLUTION
becomes unstable,
crystals form
increasing concentration
Solubility tables (pg. 324)
ionic compounds are listed as having either
high or low solubility at SATP (25°C and 100
kPa)
 anions paired with particular cations have
either:



High solubility
Low solubility
OR
Solubility Categories
High solubility = with a maximum
concentration at SATP (standard ambient
temperature and pressure) of greater than or
equal to 0.1mol/L
 Low solubility = with a maximum
concentration at SATP of less than 0.1mol/L
 Insoluble = a substance that has a negligible
solubility at SATP

Solubility of Solids
Solubility of a solid changes with temperature
 Higher solubility at higher temperatures




in industry, the solute is isolated from many
solutions by evaporating the solvent
this increases the concentration of a solution and
once it is greater than the solubility, the solute
crystallizes (precipitates) out
Solubility Curve = a graph of solubility
versus temperature
Solubility Curve of Solids (pg. 394)





Solubility is most affected
by temperature
The line shows you how
much solute can dissolve
in 100g of water at a
particular temperature.
A concentration on the
line is a saturated solution
Concentrations above the
line are supersaturated
Concentrations below the
line are unsaturated
What can I do with a solubility curve?

Calculating the amount of solute
that needs to be added to a
solution to make saturate it.

Calculating the amount of solute
that will crystallize out of solution
when the solution is cooled.
Classify as unsaturated, saturated, or supersaturated.
per
100 g
H2O
80 g NaNO3 @ 30oC
unsaturated
45 g KCl @ 60oC
saturated
50 g NH3 @ 10oC
unsaturated
70 g NH4Cl @ 70oC
supersaturated
Per 500 g H2O, 120 g KNO3 @ 40oC
saturation point @ 40oC for 100 g H2O = 66 g KNO3
So sat. pt. @ 40oC for 500 g H2O = 5 x 66 g = 330 g
120 g < 330 g
unsaturated
Describe each situation below.
(A) Per 100 g H2O, 100 g
NaNO3 @ 50oC.
Unsaturated; all solute
dissolves; clear solution.
(B) Cool solution (A) very
slowly to 10oC.
Supersaturated; extra
solute remains in solution;
still clear.
(C) Quench solution (A) in
an ice bath to 10oC.
Saturated; extra solute
(20 g) can’t remain in
solution, becomes visible.
Solubility of Gases

Gases have a higher solubility at lower
temperatures
Think: Pop
 glass of cola sitting in the refrigerator as
compared to one sitting on the kitchen
counter
 Can of pop is also stored under pressure
 Increased pressure = increased solubility

Solubility vs. Temperature for Solids
140
KI
130
Solubility
Graph
shows the dependence
of solubility on temperature
Solubility (grams of solute/100 g H2O)
120
NaNO3
110
gases
solids
100
KNO3
90
80
HCl
NH4Cl
70
60
NH3
KCl
50
40
30
NaCl
KClO3
20
10
SO2
0
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517
10 20 30 40 50 60 70 80 90 100
Solubility of Sodium Acetate
Solubility(g/100 g H2O)
150
Saturated
Supersaturated
solution
100
Unsaturated
solution
50
Video Clip
0
25
50
75
Temperature (oC)
Charles H.Corwin, Introductory Chemistry 2005, page 378
100
The
small
crystal
A
single
crystal
ofcauses
sodiumextensive
acetate,
crystallization,
and eventually
NaC2H3O2, is dropped
into a
supersatureated
solution
the solute forms
a
solid mass of NaC2H3O2.
Homework

Worksheet: Solubility Curves & Solubility Tables