Experiment 3

The following experiment demonstrates the conservation of matter in a series of chemical changes and examines the stoichiometry of these reactions. Starting from the metallic state, a sample of copper is carried through a series of chemical reactions, producing in sequence several different copper compounds, and finally is returned to the metallic state.

In order for this experiment to have a meaningful result, one must be careful not to discard any of the copper-containing materials during the course of the experiment. You will calculate the percent loss using the equation below.

The reactions described in the Pre-laboratory question #1 will be carried out in Steps I-V of the procedure. You will be required to write balanced net ionic equations in the observations section of your lab report. You will need to write many observations concerning the changes that occur when chemicals are mixed: color changes, precipitates formed, precipitates dissolved, gases evolved, etc. A few comments on writing good observations are appropriate at this point. The written observations should be very brief, yet describe the outcome of doing something to a reaction mixture (heating it, adding another chemical to it, ...). Colors are needed to describe solids, liquids, and gases. Keep in mind that terms such as "silver" and "gold" are metal names and not colors. The colors in this case are "gray" and "yellow". Another descriptive property of liquids or solutions is their transparency. If a liquid is transparent (i.e. can see light through it), then it is described as "clear". Thus apple juice is brown and clear while milk is white and opaque. The term "colorless" is used to describe a liquid or solution that has no color. For example, water should be described as simply colorless.

This experiment will be done collaboratively. Your instructor will assign pairs of students to work together on the procedure given below. The experimental work must be divided evenly between the partners (i.e. it is not acceptable for one partner to do all the experimental work and the other partner to do all the note-taking). Addtionally, each pair of students must work efficiently in order to finish the experiment within one lab period. Both partners should observe the chemical reactions; however, both partners do not need to go to the balance to weigh out the zinc, for example. Look ahead in your procedure to see if a step may be done out of sequence (i.e. something can be set up or a chemical weighed) in order to save time later. Each student will turn in individual lab reports. Although the data portions will be identical for each pair of students, the written portions (objective, procedure, observations, conclusions) will be original.