Solubility vs. Temperature for Solids
140
KI
130
Solubility
Table
• 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
NH3
KCl
70
60
50
40
30
NaCl
KClO3
20
10
SO2
0
10 20 30 40 50 60 70 80 90 100
How to determine the solubility of a given
substance?
• Find out the mass of solute needed to make
a saturated solution in 100 cm3 of water for a
specific temperature(referred to as the
solubility).
• This is repeated for each of the temperatures
from 0ºC to 100ºC. The data is then plotted
on a temperature/solubility graph, and the
points are connected. These connected
points are called a solubility curve.
How to use a solubility graph?
• IDENTIFY A SUBSTANCE ( given the
solubility in g/100 cm3 of water and the
temperature)
• Look for the intersection of the
solubility and temperature.
Example:
What substance has a
3
solubility of 90 g/100 cm
of water at a temperature
of 25ºC ?
Example:
What substance has a
3
solubility of 200 g/100 cm
of water at a temperature of
90ºC ?
Another way to use the Solubility
graph
• Look for the temperature or solubility
• Locate the solubility curve needed and
see for a given temperature, which
solubility it lines up with and visa versa.
• What is the
solubility of
potassium
nitrate at
80ºC ?
At what
temperature
will sodium
nitrate have a
solubility of
95 g/100 cm3
?
At what
temperature
will
potassium
iodide have a
solubility of
230 g/100
cm3 ?
• What is the
solubility of
sodium
chloride at
25ºC in 150
cm3 of water
?
• From the
solubility graph
we see that
sodium chlorides
solubility is 36 g.
Place this in the proportion below and solve for the
unknown solubility. Solve for the unknown quantity
by cross multiplying.
Solubility in grams = unknown solubility in grams
100 cm3 of water
other volume of water
___36 grams____ = unknown solubility in grams
100 cm3 of water
150 cm3 water
The unknown solubility is 54 grams. You can use this
proportion to solve for the other volume of water if you're given
the other solubility.
Another way!!
Determine if a solution is saturated,
unsaturated,or supersaturated.
If the solubility for a given substance places it
anywhere on it's solubility curve it is saturated.
• If it lies above the solubility curve, then it's
supersaturated,
• If it lies below the solubility curve it's an
unsaturated solution. Remember though, if the
volume of water isn't 100 cm3 to use a proportion
first as shown above.
• Sometimes you'll need to determine
how much additional solute needs to
be added to a unsaturated solution
in order to make it saturated.
• For example,30 grams of potassium
nitrate has been added to 100 cm3
of water at a temperature of 50ºC.
How many
additional grams
of solute must
be added in
order to make it
saturated?
From the graph
you can see that
the solubility for
potassium
nitrate at 50ºC is
84 grams
If there are already 30 grams
of solute in the solution, all
you need to get to 84 grams is
54 more grams
( 84g-30g = 54g)
Solubility vs. Temperature for Solids
Classify as unsaturated,
saturated, or supersaturated.
140
KI
130
Per 100 g
H2O
45 g KCl @ 60oC
50 g NH3 @ 10oC
70 g NH4Cl @ 70oC
=unsaturated
=saturated
=unsaturated
=supersaturated
Solubility (grams of solute/100 g H2O)
80 g NaNO3 @ 30oC
120
NaNO3
110
gases
solids
100
KNO3
90
80
HCl
NH4Cl
NH3
KCl
70
60
50
40
30
NaCl
KClO3
20
10
SO2
0
10 20 30 40 50 60 70 80 90 100
Describe each situation below.
(A) Per 100 g H2O, 100 g
NaNO3 @ 50oC.
(B) Cool solution (A) very
slowly to 10oC.
(C) Quench solution (A) in
an ice bath to 10oC.
Unsaturated; all solute
dissolves; clear solution.
Supersaturated; extra
solute remains in solution;
still clear.
Saturated; extra solute
(20 g) can’t remain in
solution, becomes visible.