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Exercise 9: Solutions
Introduction
Solutions consist of two parts: a solute and a solvent. In a solution the solute is the substance
that is present in the smaller amount (it is the substance that dissolves). The solvent is the
substance in solution that is present in the larger amount (it is the substance that dissolves the
solute). If the solute is a solid and the solvent is a liquid, we say the solute is soluble in the
solvent. If the solute is a liquid and the solvent is a liquid, we say they solute and solvent are
miscible. In this experiment all of the solutions will be aqueous, that is, all the solutions have
water as the solvent.
As we have already discussed, the important factors in determining whether or not a solute will
dissolve in a solvent are the nature (or types) of solute and solvent used. The expression, “like
dissolves like” is an easy reminder that a solute with characteristics similar to the solvent is
likely to dissolve in the solvent while a solute with characteristics different from the solvent is
not likely to dissolve in the solvent. For example ionic solids (composed of charged particles)
are generally soluble in polar solvents (substances that have a separation of charge). Nonpolar
covalent and polar covalent substances (substances that have no, or only a slight, separation of
charge) are not likely to be soluble in a polar substance (substances that have a separation of
charge).
However, intermolecular forces are only part of what must be considered in the solution making
process. In the exercise for this week we will examine the following aspects of the solution
making process. In procedures A and B, saturated solutions (solubility) and supersaturated
solutions will be examined. In procedure C, factors affecting the ate of solution formation will
be observed, while in part D, factors affecting the overall solubility of solutes will be examined.
Parts A and B of the procedure use several terms previously discussed in class. As a brief
refresher, saturated solutions are solutions that, at a given temperature, have as much solute
dissolved in them as possible. An unsaturated solution is a solution that, at a given temperature,
is capable of dissolving more solute. A supersaturated solution is a solution that, at a given
temperature, has more solute dissolved in it than the saturated solution. In procedure A, you will
determine the mass percent of a saturated sodium chloride solution. In part B you will attempt to
make a supersaturated solution and observe several characteristics of the solution.
In Part C of the exercise you will examine how the temperature of the solvent, particle size, and
agitation of the solute affect how quickly a solution is formed.
In Part D of the exercise you will observe how the nature of the solute, solvent and temperature
affect solubility.
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Procedures
Part A. Mass Percent of a Saturated Solution
1. Set up a steam bath as illustrated by your instructor.
2. Determine and record the mass of an empty evaporating dish.
3. Measure about 5 mL of saturated sodium chloride solution into a clean, dry evaporating dish.
Record the volume of solution used.
4. Determine and record the mass of the solution and evaporating dish.
5. Place the evaporating dish on the steam bath and heat until all the water in the evaporating
dish has evaporated (You may need to occasionally add water to the steam bath).
6. Remove the evaporating dish from the steam bath and turn off the steam bath. Let
evaporating dish cool to room temperature.
7. Determine and record the mass of the evaporating dish and solid.
8. Fill in Data Table A.
Part B. Supersaturated Solution
1. Half fill a large, clean test tube with sodium thiosulfate pentahydrate (Na2S2O3 • 5H2O).
2. Using a bunsen burner heat the test tube until all of the sodium thiosulfate pentahydrate
“melts”.
3. Allow the test tube to cool, undisturbed to room temperature.
4. After the solution has cooled to room temperature add one “seed crystal” of sodium
thiosulfate pentahydrate to the solution. Observe what happens. Feel the test tube. Record
your observations.
5. When completed, re-melt the sodium thiosulfate pentahydrate and dispose of it the waste
container.
Part C. Rate of Solution Formation
1: Agitation and Particle Size
1.
2.
3.
4.
Label four test tubes 1 through 4.
Half-fill each of the test tubes with distilled water.
Into test tubes 1 and 2 place a crystal of copper sulfate pentahydrate.
Into test tubes 3 and 4 place a small amount of powdered copper sulfate pentahydrate
(amount the same amount as in step 3).
5. Place test tubes 1 and 3 in a test tube rack with out shaking.
6. Shake test tubes 2 and 4 and the same time. Note how long it takes for each of the four test
tubes to dissolve.
7. Record the times and your observations in Data Table B.
2: Temperature Effects
1. In a 100 mL beaker heat about 30 mL of distilled water to boiling.
2. In a second 100 mL beaker and a handful of ice to about 20 mL of distilled water.
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3.
4.
5.
6.
7.
8.
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Label three test tubes 1 through 3.
Fill each of the three test tubes to a depth of about 0.5 cm with sodium chloride.
Half fill test tube 1 with the ice-water.
Half fill test tube 2 with the boiling water.
Half fill test tube 3 with room temperature water.
Do NOT shake the test tubes.
Record you observations in Data Table C.
Part D. Factors Affecting Solubility
1: Nature of Solute/Solvent
1.
2.
3.
4.
5.
6.
7.
8.
Label 8 test tubes 1 through 8.
Add about 5 mL of distilled water to each of the test tubes 1 through 4.
Add about 5 mL of methylene chloride to each of the test tubes 5 through 8.
Add a small amount of solid sodium chloride NaCl to test tubes 1 and 5.
Add a small amount of sucrose to test tubes 2 and 6.
Add a few drops of corn oil to test tubes 3 and 7.
Add a few crystals of iodine to test tubes 4 and 8.
Gently shake the test tubes and record your results in Data Table D.
2: Temperature
1. Setup a hot-water bath.
2. Place about 3 mL of distilled water into a test tube and place it in the hot water bath.
3. When the water is boiling carefully add potassium nitrate to the hot water in the test tube
until no more will dissolve (some potassium nitrate with settle to the bottom of the test tube).
4. Place the test tube in a test tube rack to cool.
5. Record your observations.
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Data Sheet for Exercise 9: Solutions
Data Table A:
Saturated Solution
Mass of empty evaporating dish
_________________ g
Volume of solution added
_________________ mL
Mass of evaporating dish plus solution
_________________ g
Mass of evaporating dish and solid
_________________ g
Mass of solution
_________________ g
Mass of solid
_________________ g
Mass percent (m/m %)
_________________
Mass/Volume percent (m/v %)
_________________
Supersaturated Solution Observations:
Data Table B:
Agitation
Test Tube
Sample
1
Crystal, unshaken
2
Crystal, shaken
3
Powder, unshaken
4
Powder, shaken
Time (seconds)
Observations
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Lab section (day, AM/PM)
Data Table C:
Temperature
Test Tube
Water
1
Ice water
2
Boiling water
3
Room temp. water
Observations
Data Table D:
Nature Solute/Solvent
Test tube
Solvent
1
2
3
4
5
6
7
8
Temperature Effect Observations:
Solute
Observations
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