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Unformatted text preview: like regular electros, but with 1/3
fewer calories. An electrolyte will conduct electricity when dissolved in water, while a nonelectrolyte will not. Finally, ionic compounds tend to have higher melting points than covalent
compounds. These are summarized as follows: Solubility Non-polar Covalent
non-polar solvents Polar Covalent
polar solvents Conductivities Non-electrolytes Non-electrolytes Melting points very low low Ionic
polar solvents (or
generally not soluble)
Electrolytes (even if
Dakota State University Page 54 of 232 Experiment 2: Compound Types General Chemistry I and II Lab Manual You will find a series of solid compounds. Run the following tests to decide if each
compound is ionic, polar covalent or non-polar covalent based on the above table. Begin by
taking very careful observations of each compound, and run each of the following tests on each
You will need two clean test tubes (one of which is dry) for each of the unknown solids. Make
sure that these test tubes are cleaned very well, and rinsed very thoroughly with distilled water.
Any contamination from tap water or other sources will seriously affect your conductivity
Put about 1 mL of water (a polar solvent) into one series of test tubes, and 1 mL of the
non-polar solvent (probably Hexane) in the other series of test tubes. Place just enough of each
solid into one water and one non-polar solvent test tube. Agitate each test tube by flicking it
several times while holding it such that it does not fly out of your hands. Note whether or not the
solid dissolved completely, dissolved partially, or did not appear to dissolve at all. Record your
“Partially dissolved” means that it is apparent that there is not as much of the solid in the
test tube remaining as you put in initially, but there is still some solid left. If the amount of solid
did not seem to decrease, it is “insoluble”. To be truly dissolved, the solution must be clear (not
necessarily colorless, but clear). If it appears cloudy, then there is still undissolved solid in the
test tube deflecting the light (called the “Tyndall effect”).
You may discard the solutions with the non-polar solvent according to the instructions
provided in lab. Keep the water solutions for the next step.
Whether the solid appears to have dissolved or not, perform this conductivity test on each
water solution. If a Pasco probe for conductivity is available, connect the probe to your
computer and set it up according to the standard Pasco procedure. You will want the “digits” to
be displayed, and probably a table. Set up the Pasco software for manual data collection, so you
can type in the sample number for each test. If the Pasco probe is not available, you will find a
multimeter set up with conductivity available.
Rinse the probe tips off very well with distilled water (you need not dry them). Rinse of
a clean watch glass with distilled water as well. Pour a little bit of the liquid from the test tube
onto the watch glass; if solid remains in t...
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