Laboratory Investigation
Name ___________________________________
Chemistry@Frisch
Date _____________________
Period _____
Constructing a Solubility Curve
PROBLEM
How is solubility measured?
INTRODUCTION
A solubility curve relates the concentration of a saturated solution to temperature. Generally, we measure the solubility of a
solute in an aqueous solution in grams of solute per 100 grams of water. Today, you will gather data and construct a solubility
curve for potassium nitrate (KNO3) and compare it with an accepted curve for that substance.
MATERIALS (per group)
Balance; beaker; Bunsen burner; graduated cylinder; potassium nitrate; safety goggles; scoop; striker; test tube; test tube
holder; test tube rack; thermometer; tongs; wire gauze
PROCEDURE
1.
Weigh a clean, dry test tube (resting in a beaker) to the nearest 0.0 1 gram. Record your data in
the data table on the next page.
2.
Your teacher will assign you the approximate mass of KNO3 to be used. Place this amount in
your test tube. Weigh the test tube again and record your data in the data table on the next page.
Group
Mass of solute
/g
1
2.5
2
3.0
3
3.5
4
4.0
5
4.5
6
5.0
3.
Add approximately 5 milliliters of water to the test tube and weigh it one more time. Record the
data in the data table on the next page.
4.
Add water to the beaker (which now serves as a water bath). Set up
the water bath like the one shown to the right..
5.
Put on safety goggles. CAUTION: Wear safety goggles whenever you
use the Bunsen burner. Light the Bunsen burner with a striker. Heat
the water bath until all of the solid just dissolves. Stir gently with
your thermometer. (CAUTION: Do not overheat, unless you intend
to spend the entire day in the laboratory!)
7.
Using a test tube holder, remove the test tube from the water bath. Stir
constantly with the thermometer and record the temperature at which
crystals of potassium nitrate first appear in the data table on the next
page.
8. Clean your work station.
CALCULATIONS
9.
Calculate the mass of KNO3 used by subtracting the mass of the empty test tube and beaker from
the mass of the test tube, beaker and KNO3. Record the result.
10. Calculate the mass of the water used by subtracting the mass of the test tube, beaker and KNO3
from the mass of the test tube, beaker, KNO3 and water. Record the result.
11. Calculate the solubility of KNO3 in grams of KNO3 per 100 g water by multiplying the mass of
KNO3 used by 100 g and dividing by the mass of the water used. Record the result.
12. Examine the solubility curve for KNO3 on the next page. Record the accepted solubility of
KNO3 at the temperature you used, and calculate the percent error of your determination. Record
the result.
13. Obtain the solubilities calculated by the other members of the class and record them in the table
below. Graph the class data in the space provided on the next page.
OBSERVATIONS
Mass of empty tube in beaker . . . . . . . . . . . . . . . . . . . . . . . . . . . _______________ g
Mass of tube, beaker and KNO3 . . . . . . . . . . . . . . . . . . . . . . . . . . _______________ g
Mass of tube, beaker, KNO3 and water . . . . . . . . . . . . . . . . . . . . _______________ g
Temperature at which crystals first appear . . . . . . . . . . . . . . . . . _______________ EC
Mass of KNO3 used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _______________ g
Mass of water used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _______________ g
Solubility of KNO3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _______________ g KNO3 per 100 g water
Accepted solubility at the temperature you used: . . . . . . . . . . . . _______________ g KNO3 Per 100 g water
Percent error of your determination: . . . . . . . . . . . . . . . . . . . . . . _______________ %
Class Data
Group Temperature / (EC)
Solubility /(g solute
per 100 g water)
Group Temperature / (EC)
1
7
2
8
3
9
4
10
5
11
6
12
Solubility /(g solute
per 100 g water)
Accepted Solubility Curve
Your Solubility Curve
CONCLUSIONS
1.
Compare your graph to the accepted solubility curve for KNO3.
2.
List the possible sources of error that might have been present in this experiment and indicate how each of these errors
would have affected the value of the experimental solubility of the compound.