Chemistry 21A
Experiment 6
SOLUTIONS AND COLLOIDS
INTRODUCTION
The most familiar solutions are liquids that are homogeneous dispersions of a solid solute in a liquid
solvent. The theory and properties of solutions can be quite complicated, but several generalizations
can be made. One of the most common rules for determining solubility is “like dissolves like”; that
is, a polar solvent (such as water) will dissolve polar compounds (salts, polar covalent compounds)
while nonpolar solvents (such as gasoline) will dissolve nonpolar compounds.
In order for salts to dissolve, the individual ions must be separated. Polar solvents have the ability to
separate ionic compounds into individual ions. Conversely, nonpolar solvents have little ability to pull
the ions of a salt apart. Therefore, salts are usually not soluble in nonpolar solvents.
The amount of solute which dissolves is dependent upon only the temperature and the type of
solvent. The rate at which a solute dissolves, however, is dependent upon (1) particle size, (2)
solvent motion, (3) temperature, and (4) the type of solvent. In this experiment, you will observe
how these factors influence the rate at which a solute dissolves.
Standard solutions are solutions of known concentration. In this experiment you will prepare a
standard solution of NaCl and calculate its concentration. Then, you will dilute your standard solution
to one of another molarity (M) and calculate the new concentration.
Physical properties that are dependent upon the number of solute particles in a solution are called
colligative properties. In this experiment, you will see the colligative effect of adding salt to water to
lower the freezing point.
Besides solutions, we can also observe suspensions and colloidal dispersions. In a suspension,
large particles simply become mixed with the solvent and may eventually settle out or can be filtered
out. In a colloidal dispersion, particles of size 10-100 Å in diameter are scattered in the solvent, but
usually do not settle out and cannot be filtered out. The difference between a true solution and a
colloid can readily be observed by a phenomena called the TYNDALL EFFECT.
EXPERIMENTAL
** The organic solvents used in this experiment are flammable. Exercise caution. Work in the hood
if possible.
Dispose of all samples as specifically directed.
It is recommended that this experiment be performed in pairs.
A. The Effect of the Nature of the Solute and the Solvent.
1. Number five (5) test tubes and place them in a test tube rack. Add 0.1 g (about the
amount you can get on the tip of a spatula) of the following substances as indicated:
Test
Test
Test
Test
Test
tube
tube
tube
tube
tube
#1:
#2:
#3:
#4:
#5:
sugar
vegetable oil (add 5 drops)
naphthalene
sodium chloride
boric acid
2. Add 3 mL of distilled water to each test tube and shake the tubes individually by tapping
against the palm of your hand.
3. IF the original solid DID NOT all dissolve after Step 2, add an additional 3 mL of distilled
water to the test tube.
4. In the data sheet, record the amount of water added to each test tube and for the
solubility, state whether each substance was insoluble (I - none of it dissolved), somewhat
soluble (SS - some of it dissolved, but not all of it) or very soluble (S - all of it dissolved).
5. Dispose of all of the mixtures in the labeled waste container in the hood.
6. Repeat the above procedure (steps 1 through 5) adding ethyl alcohol instead of water.
7. Repeat the above procedure (steps 1 through 5) adding acetone instead of water.
8. Repeat the above procedure (steps 1 through 5) adding petroleum ether instead of water.
B. Liquids Dissolved in Liquids
1. Number six test tubes and place them in a test tube rack. Add the following to each
test tube as indicated:
test
test
test
test
test
test
tube #1:
tube #2:
tube #3:
tube #4:
tube #5:
tube #6:
2
2
2
2
2
2
mL
mL
mL
mL
mL
mL
of
of
of
of
of
of
distilled water and 2 mL of ethyl alcohol
distilled water and 2 mL of acetone
distilled water and 2 mL of petroleum ether
ethyl alcohol and 2 mL of acetone
ethyl alcohol and 2 mL of petroleum ether
acetone and 2 mL of petroleum ether
Keep these tubes in the hood.
2. Cork each test tube and shake vigorously for about five seconds.
3. On the data sheet, record whether the liquids were miscible (only one layer seen), partially
soluble (two unequal layers seen), or immiscible (two equal sized layers seen).
4. Dispose of these mixtures in the labeled waste container in the hood.
C. The Effect of Surface Area and Stirring
1. Set up a boiling water bath (to be used in step 5).
2. Number three test tubes. Place a pea-sized amount of UNGROUND crystals of hydrated
cupric sulfate (copper(II) sulfate monohydrate, CuSO4 . H2O) into test tube #1. Add this
same amount of “pulverized” cupric sulfate into the other two test tubes (#2 and #3); if
pulverized cupric sulfate is not available, prepare by placing several crystals of unground
hydrated cupric sulfate into a dry mortar and grinding with a pestle. Add 5mL of distilled
water to each of the three test tubes.
3. WITHOUT heating it, stir the contents of test tube #1. On the data sheet, record the
time it takes for dissolving to be completed. (Stop stirring after 10 minutes, even if not all
of the crystals have dissolved.)
4. WITHOUT heating it, stir the contents of test tube #2. On the data sheet, record the
time it takes for dissolving to be completed.
5. Turn off the burner under the boiling water bath and immediately place test tube #3 in the
water bath and begin stirring the contents of the test tube. On the data sheet, record the
time it takes for dissolving to be completed.
6. Dispose of all of these blue solutions in the labeled waste container in the hood.
D. Preparation of a Standard Solution from a Solid
1. Carefully weigh out 2.92 g of sodium chloride and pour it through a funnel into a 50.0 mL
volumetric flask.
2. Rinse the funnel with distilled water into the volumetric flask until the flask is about halffilled with water. Remove the funnel, stopper the flask and shake vigorously until all the
sodium chloride is dissolved.
3. Add water until the bottom of the meniscus just touches the etch line on the volumetric
flask. Mix thoroughly. Pour the solution into a clean, dry beaker for use in Parts E and F of
this experiment.
4. On the data sheet, calculate the molarity of the solution that you prepared.
E. Preparation of a Standard Solution by Dilution of a Solution of Known Concentration
1. Rinse the volumetric flask twice with distilled water. You do not have to dry the flask
because you will be adding distilled water as the solvent in step 3.
2. Transfer 10.0 mL of the solution from Part D using a 10.00 mL volumetric pipette into the
rinsed 50.0 mL volumetric flask. The flask does not need to be dry to start!
3. Fill the flask with distilled water to the etch mark as in Part D. Mix thoroughly.
4. Save this solution for use in Part F. On the data sheet, calculate the molarity.
F. Freezing Point of Solutions
1. Prepare an ice-salt bath by filling a 400 mL beaker halfway with ice then stirring into this
about 20 g of sodium chloride (“rock salt”).
2. Number three test tubes, #1, #2, #3, and add the following to each as indicated:
test tube #1: 5 mL of distilled water
test tube #2: 5 mL of the solution from Part D
test tube #3: 5 mL of the solution from Part E
3. Place the three tubes in the ice-salt bath.
4. Record the temperature of the liquid in each test tube when freezing has occurred (the
liquid should be “slushy”, not fully solid!). Be careful with the thermometer!
5. All solutions from Parts D, E, and F, and the ice-salt mixture, may be discarded in the sink.
G. Saturated Solutions (Optional)
1. Place 10 mL of distilled water in a 50 mL Erlenmeyer flask.
2. Add sugar in 2 g amounts until the sugar will no longer dissolve when the flask is
swirled.
3. In the data sheet, record the amount of sugar you added up to the point at which
dissolution would no longer take place.
4. Measure the temperature of your solution.
5. The sugar solution may be discarded in the sink.
6. Calculate the solubility of sugar in g/100 mL of distilled water at this temperature in the
space provided on the data sheet.
H. Supersaturated Solutions (Demonstration)
1. Place 5 g of sodium thiosulfate in a clean, dry test tube and add 15 drops of distilled
water.
2. Place the test tube in a boiling water bath and heat until the crystals are dissolved.
3. Remove the test tube from the water bath; place a rubber stopper loosely in the mouth
of the test tube.
4. Place the test tube in a rack and let the tube cool to room temperature undisturbed.
5. CAREFULLY add one crystal of sodium thiosulfate.
6. Record your observation in the data sheet.
Name ______________________________________
Date ________________
Experiment 6: Solutions and Colloids
Data Report Sheet
A. The Effect of the Nature of the Solute and Solvent
Solvent
Solute
mL
water
soluble?
mL
soluble?
alcohol
mL
acetone
soluble?
mL
petroleum soluble?
ether
1. sugar
2. vegetable
oil
3. C10H20
naphthalene
4. NaCl
5. boric acid
B. Liquids Dissolved in Liquids
Test Tube 1 (water and alcohol) __________________________________________________
Test Tube 2 (water and acetone) _________________________________________________
Test Tube 3 (water and petroleum ether) __________________________________________
Test Tube 4 (alcohol and acetone) ________________________________________________
Test Tube 5 (alcohol and petroleum ether) _________________________________________
Test Tube 6 (acetone and petroleum ether) _________________________________________
C. The effect of Surface Area and Stirring
Time for Dissolution:
Tube 1 __________
Tube 2 __________
Tube 3 __________
D. Preparation of a Standard Solution of Known Concentration, from a Solid.
Molarity of the solution prepared in Part D __________________________________________
Calculations:
E. Preparation of a Standard Solution of Known Concentration, by Dilution of a Solution of Known
Concentration.
Molarity of the solution prepared in Part E __________________________________________
Calculations:
F. Freezing/Melting Point of Solutions
Observed freezing point:
Test tube 1 (distilled water):
____________________
Test tube 2 (solution from Part D):
____________________
Test tube 3 (solution from Part E):
____________________
G. Saturated Solutions
Grams of sugar added to 10 mL of water ___________________________________________
Solubility (grams/100 mL H2O) ___________________________________________________
Calculations:
H. Supersaturated Solutions – Observations.
Name ______________________________________
Date _____________________
Experiment 6: Solutions and Colloids
Questions
1. Did YOUR results in Part A and Part B support the statement “like dissolves like”? GIVE SPECIFIC
EXAMPLES for EACH Part. Note: water is a very polar solvent, petroleum ether is a nonpolar solvent;
sodium chloride is a very polar solute, naphthalene is a nonpolar solute.
2. Interpret YOUR freezing point data from Part F in terms of colligative properties.
3. Describe HOW you would MAKE each of the following solutions. Indicate not just the mass of
SOLUTE needed BUT ALSO the amount of SOLVENT needed AND what you would DO. (All are
aqueous solutions.)
a) 1.00 liter of 1.50 M NaCl solution
b) 50.00 g of a 0.500% (w/w) NaCl solution
c) 50.0 mL of a 0.500% (w/v) NaCl solution
d) 250.0 mL of a 0.300 M glucose solution (MM of glucose = 180.2 g/mol)