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 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.
In this experiment, you will examine the relationship between a compound's polarity and its solubility in water.
Goal
_____________________________________________________________________________________
Equipment
safety goggles 10 small test tubes
1 spatula 1 test-tube rack
1 dropper pipet 1 plastic wash bottle
_____________________________________________________________________________________
Materials
sodium chloride, NaCl hexane, C6H14
sucrose, C12H22O11 kerosene, C12-C15
sodium thiosulfate, Na2S2O3 1,1,2-trichloro-1,2,2-trifluoroethane(TTE), C2Cl3F3
calcium carbonate, CaCO3 glycerin, C3H8O3
potassium sulfate, K2SO4 distilled water
ethanol, C2H5OH
_____________________________________________________________________________________
Safety
· Note the Safety Symbols used here and in the Procedure section. Review safety information on pages
7-10.
· Always wear safety goggles when working in the lab.
· Ethanol, hexane, and kerosene are flammable. Do not use these substances near open flames.
Procedure
Copy Table 26.1 into your laboratory notebook. As you perform the experiment, record your results and
observations in the table.
1. Record Table 26.1 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 substance 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 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 Table 26.1.
3. Dispose of the hexane, kerosene, and TTE samples as directed by your teacher. Dispose of all other samples by flushing them, with water, down the drain. Rinse the test tubes.
Data Record
TABLE 26.1 RESULTS AND OBSERVATIONS
|
|
|
|
|
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
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 tested are polar or nonpolar?
4. Which of the liquid substances tested are polar? Which are nonpolar?