Group
Name
Date
Period
Solubility and Solubility Curves
When we talk about the mixing of two or more substances together in solution we must consider
solubility. Simply defined, it is a measure of how much solute will dissolve into the solvent.
A solution consists of a solute dissolved in a solvent. The solute may be a solid, liquid or gas.
The most common solvent is water (solutions in which water is the solvent are called aqueous
solutions), but there are many other possible solvents, e.g. ethanol, hexane, 1,1,1-trichloroethane.
When a substance dissolves, its particles become spread out through the solvent. However, there
is a limit to the amount of solute that can be dissolved in a given volume of solvent at a given
temperature. When this limit is reached, the solution is said to be ‘saturated’, and no more solute
can be dissolved. (e.g. 100 cm3 of water can dissolve 35.8 g of NaCl at 25 oC)
Solubility in water at a given temperature is expressed as the number of grams of solute that will
dissolve in 100 g of water at that temperature. (e.g. The solubility of baking soda (NaHCO3) at 25
o
C is 10.2 g / 100 g H2O is less soluble than NaCl (35.8 g / 100 g H2O) at this temperature.)
The variation of the solubility of a substance with temperature can be shown using solubility
curves.
The solubility of most solids increases as temperature increases.
However, the solubility of gases usually decreases as temperature increases.
Temperature (°C)
10
30
50
70
90
Grams of Material Needed to Make a Saturated Solution in 100 g of Water
Copper Sulfate Calcium Hydride Sodium Carbonate Lithium Chloride
10
60
160
20
25
64
330
25
65
68
420
33
80
74
460
40
90
76
600
48
1. If 65g of copper sulfate is dissolved is 100g of water at 50ºC, is the resulting solution
saturated, unsaturated, or supersaturated?
2. If 80g of calcium hydride is dissolved is 100g of water at 90ºC, is the resulting solution
saturated, unsaturated, or supersaturated?
3. If 20g of lithium chloride is dissolved is 100g of water at 30ºC, is the resulting solution
saturated, unsaturated, or supersaturated?
4. How many grams of sodium carbonate can be dissolved in 100g of water at 70°C?
5. A saturated solution of copper sulfate contains 100g of water. If the saturated solution is
cooled from 70°C to 30°C a supersaturated solution is formed. How many grams of
copper sulfate will precipitate? (how many grams can not dissolve?)
6. Which substance is most soluble at 10°C?
7. Which substance’s solubility is least effected by temperature?
Complete the graph below using the data for solubility for several substances.
Water
Temperature
(°C)
0
10
20
30
40
50
60
70
80
90
100
CuSO4 dissolved
(grams per 100g H2O)
KCl dissolved
(grams per 100g H2O)
KNO3 dissolved
(grams per 100g H2O)
23.1
27.5
32.0
37.8
44.6
53.2
61.8
72.8
83.8
98.9
114.0
28.1
31.2
34.2
29.4
33.3
37.2
40.0
45.8
45.8
55.2
51.3
65.6
56.3
77.3
1. What type of solution does each line represent?
2. The areas above each line, what type of solutions do they represent?
3. The areas above each line, what type of solutions do they represent?
4. What mass, in grams, of potassium chloride (KCl) will dissolve in 100 grams of water at 70°C?
What mass of CuSO4 will dissolve at this same temperature?
5. You dissolve 50g of KNO3 in 100 grams of water at 90°C producing an unsaturated solution.
How much more KNO3 would you have to add to form a saturated solution at 90°C?
6. What is the minimum mass (in grams) of 90°C water necessary to dissolve 50g of KNO3?
Show your work.
Types of Concentration Units
Mass Percent - Percent by mass of a component in a mixture
Volume Percent - Percent by volume of a component in a mixture
Parts per Million (ppm) - Parts (mass or volume) of solute found in 1,000,000 parts (mass or
volume) of solution
Parts per Billion (ppb) - Parts (mass or volume) of solute found in 1,000,000,000 parts (mass or
volume) of solution
Mass/Volume Percent
(Mass or Volume %) = (Mass or Volume Solute/Mass or Volume Solution)
(Mass or Volume %)= (Mass or Volume Solute/(Mass or Volume Solute + Mass or Volume
Solvent)
Part per Million/Billion
(%) = (Parts Solute/1,000,000 or 1,000,000,000 Parts Solution)
Move decimal 4 places for parts per million (to left to find percentage and to right to find parts)
Move decimal 7 places for parts per billion (to left to find percentage and to right to find parts)
Write a paragraph summarizing what you demonstrated in this lab. Include the following
five words/phrases: solution, unsaturated solution, saturated solution, supersaturated solution
and seed crystal. With each word include an example of how it applied to the lab.