Chem 142 Lab 2 Chemical Composition of Compounds

Chemical Composition of Compounds

Demonstration

Below are many of the experimental steps you will perform in this lab. Be sure to consult the procedure for the detailed instructions. Click on an image to open an enlarged view.

1.		In this lab, you will use tongs, a clay triangle, an iron ring, three porcelain crucibles, and a metal spatula.
2.		You will heat three different samples: a strip of Mg metal, a copper(II) carbonate hydroxide compound, and a KCl/KClO₃ mixture. In general, for each sample, you will need to 1) weigh the crucible and cover, 2) add the sample to the crucible, 3) weigh the crucible/cover/sample, 4) heat the crucible/cover/sample, 5) let everything cool, and 6) weigh the crucible/cover/product.
3.		Inspect the crucibles for cracks and clean them thoroughly. Some crucibles will be stained, like the one on the right in the picture, and are okay to use as long as you have ensured they are clean and free from debris left over from a previous reaction that could adversly affect your results.
4.		Practice using the tongs to move the crucibles and their lids. Once you have washed them you do not want to touch them with your fingers. Also, once they have been heated, they will be very hot and you will need to be able to move them only using the tongs.
5.		The technique shown is correct, but takes a little practice so that the crucible does not slip out and fall.
6.		Your final setup will look like this once you have put your sample in the crucible and . Remember, many of the components will be very hot but not look any different than they do when they are cool. Make sure you know how to work with your setup before igniting the Bunsen burner and heating the crucible.
7.		A correctly adjusted Bunsen burner will have a blue flame with a blue inner cone. Many of the burners available in the lab will need adjustments to the air and gas flows to obtain an optimal flame. Your TA will demonstrate and assist with the adjustment of the Bunsen burners.
8.		Position the ignited Bunsen burner under the assembled setup and heat the crucible and its contents according to the procedure instructions..
9.		The tip of the blue inner cone is the hottest part of the flame. Follow the procedural steps to heat the crucible red hot or, by increasing the distance between the crucible and inner blue cone, heating it gently in order to control the reaction of the sample.