Solubility Curves

• Day 65 – Solubility and Saturation - Solubility Curves

• Lesson: PPT, Try This Activity page 317 old text demo

• Handouts: 1. Solution Handout, 2. Solubility Curves Assignment.

• Text: 1. P. 392-396- solutions/ gases • HW: 1. P. 397 # 1-9  

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.

Solubility Curve

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

shows the dependence of solubility on temperature

gases

solids

Each substance has its own unique solubility which can

be displayed on a graph

Solubility depends on the solute, the solvent, and the temperature.

Determine if a solution is saturated, unsaturated, or supersaturated.

• If the solubility for a given substance places itanywhere on it's solubility curve it is saturated.• If it lies above the solubility curve, then it’ssupersaturated,• If it lies below the solubility curve it's anunsaturated solution. Remember though, if the volume

of water isn't 100 cm3 to use a proportion first.

Solubility curve

Saturated

Unsaturated

Supersaturated

Formation of a Saturated Solution

Dynamic equilibrium:  rate  of crystallization = rate of dissolving

A Supersaturated Solution

Solubility curve• Any point on a line 

represents a saturated solution. 

• In a saturated solution, the solvent contains the maximum amount of solute.

• Example• At 90oC, 40 g of NaCl(s) in

100g H2O(l) represent a saturated solution.

Solubility curve• Any point below a line 

represents an unsaturated solution. 

• In an unsaturated solution, the solvent contains less than the maximum amount of solute.

• Example• At 90oC, 30 g of NaCl(s) in

100g H2O(l) represent an unsaturated solution. 10 g of NaCl(s) have to be added to make the solution saturated.

Solubility curve• Any point above a line represents 

a supersaturated solution. • In a supersaturated solution, the

solvent contains more than the maximum amount of solute. A supersaturated solution is very unstable and the amount in excess can precipitate or crystallize.

• Example• At 90oC, 50 g of NaCl(s) in 100g

H2O(l) represent a supersaturated solution. Eventually, 10 g of NaCl(s) will precipitate.

Solubility curveAny solution can be made saturated, unsaturated, or supersaturated by changing the temperature.

Classify as unsaturated, saturated, or supersaturated.Classify as unsaturated, saturated, or supersaturated.

per100

gH2

O

80 g NaNO3 @ 30oC

45 g KCl @ 60oC

50 g NH3 @ 10oC

70 g NH4Cl @ 70oC

=unsaturated

=saturated

=unsaturated

=supersaturated

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

gases

solids

To

Sol.

To

Sol.

Solids dissolved in liquids Gases dissolved in liquids

As To , solubility As To , solubility

How to solve solubility curve problems

• Look for the intersection of the solubility and temperature

• Least soluble = lowest line at temp• Most soluble = highest line at temp• If given different amount of water• Sometimes you'll need to determine how much

additional solute needs to be added to an unsaturated solution in order to make it saturated.

For example,30 g 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 g is 54 more grams ( 84g-30g )

So sat. pt. @ 40oC for 500 g H2O = 5 x 66 g = 330 g

120 g < 330 g unsaturated

saturation point @ 40oC for 100 g H2O = 66 g KNO3

Per 500 g H2O, 120 g KNO3 @ 40oC

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

gases

solids

0 10 20 30 40 50 60 70 80 90 100

What substancehas a solubility of90 g/100 cm3 ofwater at atemperature of25ºC ?

What substance has a solubility of 100 g/50 cm3 of water at a temperature of 90ºC ?

What is the solubility of potassium nitrate at 80ºC ?

At whattemperature willsodium nitratehave a solubilityof 95 g/100cm3 ?

At whattemperature willpotassium iodidehave a solubility of115 g/50 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.

36g NaCl

100 cm3x # g NaCl=150 cm3 

54g NaCl=

Which salt is the least soluble in water at 20C°?

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for SolidsS

olub

ility

(gr

ams

of s

olut

e/10

0 g

H2O

)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl

KClO3

SO2

gases

solids

1. Which salt shows the least change in solubility from 0°Cto 100°C?2. A saturated solution of potassium chlorate is formedfrom 100 g of water. If the solution is cooled from 80°C to50°C, how many grams of precipitate are formed?3. What compound shows a decrease in solubility from 0°Cto 100°C?

A. Per 100 g H2O, 100 g NaNO3 @ 50oC.

B. Cool solution (A) very slowly to 10oC.

Describe each situation below.

C. Quench solution (A) in an ice bath to 10oC.

Unsaturated; all solutedissolves; clear solution.

Supersaturated; extrasolute remains in solution; still clear.

Saturated; extra solute(20 g) cannot remain insolution, becomes visible