The Solvent Properties of Water
Purpose:
To examine the relationship between a compound’s polarity and its solubility in water.
Background:
“Oil and water don’t mix!” You’ve probably heard this phrase before. Though this
phrase is true, there are plenty of substances that do dissolve in water. The polar nature
of the water molecule is largely responsible for its remarkable solvent action. Because
of its polarity, water is able to dissolve ionic compounds, such as sodium chloride and
copper sulfate, and polar covalent compounds, such as sugar and ammonia. Many
chemical reactions and most biochemical reactions take place in water.
Similarly, many substances dissolve in oily, nonpolar solvents, such as gasoline
and kerosene. In general, only nonpolar molecules will dissolve in nonpolar solvents.
This is the basis for the phrase “like dissolves like.”
In this experiment, you will examine the relationship between a compound’s
polarity and its solubility in water.
Materials:
Safety goggles
10 small test tubes
1 test-tube rack
1 Wash bottle w/ DI water
Sodium chloride, NaCl
Sucrose, C12H22O11
Sodium thiosulfate, Na2S2O3
Calcium carbonate, CaCO3
Potassium sulfate, K2SO4
Ethanol, C2H5OH
Hexane, C6H14
Glycerin, C3H8O3
Safety:
1) Wear your safety goggles
2) Ethanol and hexane are flammable. Do not use these substances near open
flames.
3) Avoid skin contact with these chemicals. Many of them are toxic.
4) Follow all disposal instructions
5) Wash your hands before leaving the laboratory.
Procedure:
As you perform the experiment, record your results and observations in the data table.
1) Record the chemical formula, physical state, and color of each of the substances
in the Materials section, with the exception of distilled water.
2) Test each of the substances for water solubility. Add 3-4 mL of distilled water to
each small test tube. Add a very small quantity of the substances to be tested to
an individual test tube. For solids, use a sample about the size of a match head.
For liquids, use one drop. Be careful not to contaminate the chemicals with one
another.
Flick the test tube gently and note what happens. If all of the substance
dissolves, add another small quantity and flick gently. Repeat the process
several more times if the material continues to dissolve. Describe each
substance as insoluble, slightly soluble, or very soluble, based on its behavior.
Record these descriptions in the data table.
3) Dispose of the material as directed. Rinse the test tubes and store upside down
for the next class.
Name:_______________________ Lecture Teacher:__________ Period______
Pre-lab Questions:
1. Explain why water is such an excellent solvent.
2. Using the phrase “like dissolves like,” explain why gasoline and oil do not dissolve in
water.
3. Define the terms solvent and solute.
4. Which substances used in this experiment are flammable?
Data Table: Results and Observations
Substance
Formula
Physical State
Sodium chloride
Glycerin
Sucrose
Sodium thiosulfate
Calcium carbonate
Hexane
Potassium sulfate
Ethanol
Solubility in Water
Analysis and Conclusions:
1. Polar and ionic substances generally dissolve in water; nonpolar substances do
not. Explain.
2. Based on the fact that calcium carbonate is an ionic compound, you may be
puzzled by your experimental results for this compound. Propose an explanation
for the solubility of calcium carbonate.
3. What basis can you use to decide whether the liquids are polar or nonpolar?
Which of the liquid substances tested are polar? Which are nonpolar?
4. Give the structural formulas of the liquids that were tested in this experiment. Do
these formulas support the solubility data obtained? Explain.
Glycerin (C3H8O3)
Hexane (C6H14)
Ethanol (C2H5OH
5. Based on the results of this lab, develop a hypothesis about how soaps and
detergents are able to emulsify oils and greases in a solution of water.
6. Sodium chloride readily dissolves in water, however it does not dissolve in
benzene. Explain why this happens.