1. Obtain and wear goggles.
2. Measure and record the mass of a clean, dry crucible without cover. Obtain about 1 g of the unknown copper chloride hydrate and place it in the crucible. Use a spatula to break up any large pieces of the substance by pressing the pieces against the wall of the crucible. Measure and record the mass of the crucible with compound.
3. Set up a ring stand, ring, and clay triangle for heating the sample. Rest the crucible on the clay triangle. Set up a lab burner and ignite the burner away from the crucible. Adjust the burner to get a small flame.
4. Hold the burner in your hand and move the flame slowly back and forth underneath the crucible to gently heat the sample. Do not overheat the compound. Note the color change, from blue-green to brownish, as the water of hydration is driven out of the crystals. When the sample has turned brown, gently heat the crucible for two more minutes.
5. Remove and turn off the burner. Cover the crucible and allow the sample to cool for about ten minutes.
6. Remove the crucible cover and inspect your sample. If you see any blue-green crystals, reheat the sample until the crystals have turned brown.
7. Measure and record the mass of the cool crucible of your copper chloride sample.
8. Transfer the brown solid to a clean and empty 50 mL beaker. Rinse out the crucible with two
8 mL aliquots of distilled water and pour the water into the 50 mL beaker. Gently swirl the
beaker to completely dissolve the solid. Note that the color of the solution is green as the
copper ions are rehydrated.
9. Measure out about 20 cm of aluminum wire, coil the wire, and place the wire in the beaker of solution so that it is completely immersed in the copper chloride solution. Note that the reaction produces a gas, elemental copper is forming on the surface of the aluminum wire,
and the color of the solution is fading. The reaction will take about 30 minutes to complete.
10. When the reaction is done, the solution will be colorless. Most of the elemental copper will be on the aluminum wire. Add 5 drops of 6 M HCl solution to dissolve any insoluble aluminum salts in the mixture, which should make the solution clear. CAUTION: Handle the hydrochloric acid with care. It can cause painful burns if it comes in contact with the skin.
The Determination of a Chemical Formula
11. Use a glass stirring rod to scrape off as much copper as possible from the Al wire. Slide the wire up the wall of the beaker and out of the solution with the glass stirrer and rinse off any remaining copper with distilled water. If any of the copper refuses to wash off the aluminum wire, wash it with one or two drops of 6 M HCl solution. Put the Al wire aside.
12. Collect and wash the copper produced in the reaction. a. Set up a Büchner funnel for vacuum filtration.
b. Obtain a piece of filter paper. Measure and record its mass, and then place the filter paper
on the funnel. Start the vacuum filtration.
c. Use small amounts of distilled water to wash all of the copper onto the filter paper on the
Büchner funnel. Use the glass stirring rod to break up the larger pieces of copper.
d. Wash the copper twice more with small amounts of distilled water.
13. Turn off the suction on the vacuum filtration apparatus. Add 10 mL of 95% ethanol to the copper on the filter paper and let it sit for about 1 minute. Turn the suction back on and let the vacuum filtration run for about five minutes.
14. Measure and record the mass of a clean, dry watch glass. Transfer the copper to the watch glass. Make sure that you have scraped all of the copper onto the watch glass.
15. Dry the watch glass of copper under a heat lamp or in a drying oven for five minutes. When the watch glass is cool enough to touch, measure the mass of the watch glass plus copper. Repeat the drying and weighing of the copper until you are sure that it is completely dry.
16. Dispose of the copper, aluminum wire, and filtered liquid as directed.