Laboratory Techniques I, CHY 114
Chemistry Department, University of Southern Maine

The blue color of Cu²⁺ ions disappears from the solution as magnesium
(silver solid at left) converts Cu²⁺ to metallic copper (reddish solid at right).

Why does this reaction produce bubbles?

A Colorful Sequence of Copper Reactions

Assignment

1. Use the index of your class textbook to learn all you can about copper and its compounds.
2. To learn about the lab operations of this experiment, read Sections V through VII of the Laboratory Handbook for General Chemistry.
3. In your class textbook, review balancing chemical equations.

Goal

By carrying out a series of reactions involving copper compounds, you will learn some basic lab operations, including weighing, measuring liquid volumes, heating solutions, and transferring substances between vessels.

Overview

The law of conservation of mass states that matter can be neither created nor destroyed. Because matter is composed of atoms that are unchanged in a chemical reaction, it follows that mass must be conserved as well. If you subject a measured mass of copper metal to a series of chemical reactions, producing a series of different copper compounds, and finally recover the copper metal, the mass of copper recovered should equal the mass of copper originally used.

In this experiment, you will convert copper metal, Cu(s), into blue copper(II) ions in solution, Cu²⁺(aq); then to insoluble, blue copper(II) hydroxide, Cu(OH)₂(s); then to black, insoluble copper(II) oxide, CuO(s); back to copper(II) ions in solution; and finally, back to copper metal.

You will compare the weight of your recovered copper with the starting amount to see how well you carried out the procedures.

Preparing for Lab

The following problems require calculations similar to those called for in the report on this experiment. Learn how to work these problems, showing your calculations with units. Similar questions may appear on your prelaboratory quiz. For guidance, study the Procedure and Report Form for this experiment. For problems involving calculation, answers are provided.

1. A 54.444-gram beaker and a piece of copper wire together weigh 54.945 g. You dissolve this wire in nitric acid (HNO₃), carry out a series of reactions, and ultimately recover your copper in powdery form in the same beaker. After thorough drying, the beaker and wire together weigh 54.866 g. Calculate the percent recovery of copper. (Answer: 84.2%)
2. Following are brief descriptions and equations for the reactions you will carry out in this experiment. All reactants and products are shown. Balance each equation. Remember that a balanced equation has the same number of atoms of every element on both sides. In addition, it has the same total of ionic charges on both sides.
   
   a) In Part 1, a known mass of copper is oxidized with nitric acid, forming copper (II) ion in solution:
   
   Cu(s) + H⁺(aq) + NO₃^-(aq) --> Cu²⁺(aq) + NO₂(g) + H₂O(l) (Remember that charges must balance, too.)
   
   b) In Part 2, the copper(II) ions are precipitated as insoluble copper(II) hydroxide:
   
   Cu²⁺ (aq) + (OH)^-(aq) --> Cu(OH)₂(s)
   
   c) In Part 3, the precipitate is heated to form copper(II) oxide:
   
   Cu(OH)₂(s) --> CuO(s) + H₂O(l)
   
   d) In Part 4, the copper(II) oxide is dissolved in sulfuric acid, yielding copper(II) ions in solution again:
   
   CuO(s) + H⁺(aq) --> Cu²⁺(aq) + H₂O(l)
   
   e) Finally, in Part 5, magnesium metal is added to the copper(II) ion solution to form copper metal:
   
   Mg(s) + Cu²⁺(aq) --> Mg²⁺(aq) + Cu(s)
   
   During this reaction, a side reaction also occurs between magnesium and hydrogen ions of the sulfuric acid:
   
   Mg(s) + H⁺(aq) --> Mg²⁺(aq) + H₂(g)
   
   
3. On the Syllabus page, use the link "Recognizing Chemical Hazards" to find out the hazards associated with substances you use and make in this experiment.

Procedures

Download and print the Procedure for this experiment. Study it carefully after reading this page. It's a good idea to translate the procedure into step-by-step instructions for your lab work. Bring the printed procedure and your instructions with you to lab. Once per semester, you might earn a free perfect quiz score for bringing good translated instructions.

Report

Download and print the Report Form for this experiment. Bring it with you to lab.

You will write your first abstract for this report. Click HERE for full instructions on writing abstracts.

If it is not convenient for you to return to this web page online, you might wish to print it as well.