1. 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 solutions/ gases
HW: 1. P # 1-9

2. 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.

3. Each substance has its own unique solubility which can
Solubility Curve
Solubility vs. Temperature for Solids
140 KI
130
120
shows the dependence of solubility on temperature
gases
solids
NaNO3
110
100
KNO3 90
Each substance has its own unique solubility which can
be displayed on a graph 80
HCl
NH4Cl 70
Solubility (grams of solute/100 g H2O) 60
NH3
KCl 50
“Solubility Curves for Selected Solutes”
Description: This slide is a graph of solubility curves for 10 solutes. It shows the number of grams of solute that will dissolve in 100 grams of water over a temperature range of 0cC to 10 cC.
Basic Concepts
The maximum amount of solute that will dissolve at a given temperature in 100 grams of water is given by the solubility curve for that substance.
When the temperature of a saturated solution decreases, a precipitate forms.
Most solids become more soluble in water as temperature increases, whereas gases become less soluble as temperature increases.
Teaching Suggestions
Use this slide to teach students how to use solubility curves to determine the solubilities of various substances at different temperatures. Direct their attention to the dashed lines; these can be used to find the solubility of KClO3 at 50 cC (about 21 g per 100 g of H2O). Make sure students understand that a point on a solubility curve represents the maximum quantity of a particular solute that can be dissolved in a specified quantity of solvent or solution at a particular temperature. Point out that the solubility curve for a particular solute does not depend on whether other solutes also are present in the solution (unless there is a common-ion effect; this subject usually is covered at a later stage in a chemistry course).
Questions
Determine the solubilities (in water) of the following substance at the indicated temperatures: NH3 at 50 oC; KCl at 90 oC; and NaNO3 at 0 oC.
Which of the substances shown on the graph is most soluble in water at 20 oC? Which is lease soluble at that temperature? For which substance is the solubility lease affected by changes in temperature?
Why do you think solubilities are only shown between 0 oC and 100 oC?
In a flask, you heat a mixture of 120 grams of KClO3 and 300 grams of water until all of the KClO3 has just been dissolved. At what temperature does this occur? You then allow the flask to cool. When you examine it later, the temperature is 64 oC and you notice a white powder in the solution. What has happened? What is the mass of the white powder?
Compare the solubility curves for the gases HCl, NH3, and SO2) with the solubility curves for the solid solutes. What generalizations(s) can you make about the relationship between solubility and temperature?
According to an article in an engineering journal, there is a salt whose solubility in water increases as the water temperature increases from 0 oC to 65 oC. The salt’s solubility then decreases at temperatures above 65 oC, the article states. In your opinion, is such a salt likely to exist? Explain your answer. What could you do to verify the claims of the article? 40 30
Solubility depends on the solute, the solvent, and the temperature.
NaCl
KClO3 20 10
SO2

4. 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.

5. Solubility curve Saturated Supersaturated Unsaturated
“Solubility Curves for Selected Solutes”
Description: This slide is a graph of solubility curves for 10 solutes. It shows the number of grams of solute that will dissolve in 100 grams of water over a temperature range of 0cC to 10 cC.
Basic Concepts
The maximum amount of solute that will dissolve at a given temperature in 100 grams of water is given by the solubility curve for that substance.
When the temperature of a saturated solution decreases, a precipitate forms.
Most solids become more soluble in water as temperature increases, whereas gases become less soluble as temperature increases.
Teaching Suggestions
Use this slide to teach students how to use solubility curves to determine the solubilities of various substances at different temperatures. Direct their attention to the dashed lines; these can be used to find the solubility of KClO3 at 50 cC (about 21 g per 100 g of H2O). Make sure students understand that a point on a solubility curve represents the maximum quantity of a particular solute that can be dissolved in a specified quantity of solvent or solution at a particular temperature. Point out that the solubility curve for a particular solute does not depend on whether other solutes also are present in the solution (unless there is a common-ion effect; this subject usually is covered at a later stage in a chemistry course).
Questions
Determine the solubilities (in water) of the following substance at the indicated temperatures: NH3 at 50 oC; KCl at 90 oC; and NaNO3 at 0 oC.
Which of the substances shown on the graph is most soluble in water at 20 oC? Which is lease soluble at that temperature? For which substance is the solubility lease affected by changes in temperature?
Why do you think solubilities are only shown between 0 oC and 100 oC?
In a flask, you heat a mixture of 120 grams of KClO3 and 300 grams of water until all of the KClO3 has just been dissolved. At what temperature does this occur? You then allow the flask to cool. When you examine it later, the temperature is 64 oC and you notice a white powder in the solution. What has happened? What is the mass of the white powder?
Compare the solubility curves for the gases HCl, NH3, and SO2) with the solubility curves for the solid solutes. What generalizations(s) can you make about the relationship between solubility and temperature?
According to an article in an engineering journal, there is a salt whose solubility in water increases as the water temperature increases from 0 oC to 65 oC. The salt’s solubility then decreases at temperatures above 65 oC, the article states. In your opinion, is such a salt likely to exist? Explain your answer. What could you do to verify the claims of the article?
Unsaturated

6. Formation of a Saturated Solution
Dynamic equilibrium: rate of crystallization = rate of dissolving

7. A Supersaturated Solution

8. 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.

9. 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.

10. 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.

11. Solubility curve
Any solution can be made saturated, unsaturated, or supersaturated by changing the temperature.

12. Classify as unsaturated, saturated, or supersaturated.
Solubility vs. Temperature for Solids
Solubility (grams of solute/100 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
Classify as unsaturated, saturated, or supersaturated.
80 g 30oC
45 g 60oC
50 g 10oC
70 g 70oC
=unsaturated
per
100 g
H2O
=saturated
=unsaturated
=supersaturated

13. Solids dissolved in liquids Gases dissolved in liquidsTo
Sol. To
Sol.
As To , solubility
As To , solubility

14. 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.

15. 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 )

16. Solubility vs. Temperature for Solids
Solubility (grams of solute/100 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
So sat. 40oC for 500 g H2O = 5 x 66 g = 330 g
120 g < 330 g unsaturated
saturation 40oC for 100 g H2O = 66 g KNO3
Per 500 g H2O, 120 g 40oC

17. What substance has a solubility of 90 g/100 cm3 of water at a temperature of 25ºC ?

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

19. What is the solubility of potassium nitrate at 80ºC ?

20. At what temperature will sodium nitrate have a solubility of 95 g/100cm3 ?

21. At what temperature will potassium iodide have a solubility of 115 g/50 cm3 ?

22. 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 cm3 x
# g NaCl=
150 cm3
54g NaCl =

23. Which salt is the least soluble in water at 20C°?
Solubility vs. Temperature for Solids
Solubility (grams of solute/100 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
Which salt is the least soluble in water at 20C°?

24. 1. Which salt shows the least change in solubility from 0°C to 100°C? 2. A saturated solution of potassium chlorate is formed from 100 g of water. If the solution is cooled from 80°C to 50°C, how many grams of precipitate are formed? 3. What compound shows a decrease in solubility from 0°C

25. Describe each situation below.
Unsaturated; all solute
dissolves; clear solution.
Per 100 g H2O, 100 g 50oC.
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) cannot remain in
solution, becomes visible