Either bring your own aluminum can or use the pieces provided in the lab. You will need a piece of scrap aluminum about 7.5 cm by 5.0 cm that weighs 1.0 to 1.1 grams.
2. Scrape both sides of the piece (using sandpaper) to remove the paint and lacquer (this will speed the dissolving process GREATLY, and give a more accurate starting mass).
3. Weigh the cleaned piece of aluminum on the analytical balance to the nearest milligram.
4. Cut the weighed piece of aluminum into small pieces (for more rapid dissolving) and place the pieces in a 250-mL beaker.
5. MAKE SURE YOU ARE WEARING YOUR SAFETY GOGGLES! Working under the fume hood, add 50 mL of 1.4M potassium hydroxide solution to the beaker.
6. Heat the mixture on the electric hot plates provided. If the liquid level drops to half of its original value, add distilled water to restore the original volume. During the reaction, the mixture will turn dark grey due to silicon impurities, residual paint, plastic liners, etc. No more than thirty minutes should be required to dissolve the sample. The final liquid volume should be about 60% of the original volume. The reaction is complete when the evolution of hydrogen ceases.
7. Filter the cooled solution to remove any solids remaining. The easiest filtration uses the Büchner funnel and water suction. Read the separate section on the assembly and use of this device. Be sure to use the safety trap, because in this first filtration you must save the filtrate (the solution). If you don't use the trap and there is even a small interruption in the water flow, tap water can suck back into your solution and contaminate it.
8. Discard the dark solid trapped in the filter paper and SAVE the solution for use in the next part of the experiment. (Don't waste time trying to recover the small amount of alum that forms in the beaker or suction flask).
9. Transfer the CLEAR (no suspended matter) filtrate to a clean 250-mL beaker.
10. If the beaker feels warm, place it in an ice water bath.