In the lab, students are given a 1.5 gram samples of copper. The copper is taken through a series of five chemical reactions ending with the precipitation of solid copper. After the five reactions, students are asked to return their 1.5 gram samples of copper to the teacher.
My dear friend and fellow AP chemistry teacher suggested that I use this lab during the first week of AP chemistry to review and reinforce lab techniques, for example, making solutions, diluting solutions, and decanting liquids. The experience prepared students for kinetics, equilibrium, and titration labs to come.
Here is a brief overview of the lab, and you’ll find my co-worker’s lab instructions attached.
Conversion 1: Convert copper turnings to copper(II) nitrate
Students dilute 15.8 M nitric acid to 8 M. They then react the given copper turnings with the diluted acid. Warning! Nitrogen dioxide, a brown gas, is released, which requires using the fume hood. When the reaction is complete, students will have a beautiful, blue solution of copper(II) nitrate.
Skills: measurement, dilution, selection of appropriate glassware, selection of appropriate tools for measurement, use of the fume hood
Conversion 2: Convert copper(II) nitrate to copper(II) hydroxide
Using pH paper or litmus paper, students test the copper(II) nitrate solution. Then, they make a solution of 6 M NaOH and test the solution with pH paper or litmus paper. The reaction of copper(II) nitrate and NaOH is slowly performed in an ice-water bath. Students use the indicator to test the progress of the reaction. The reaction is complete when the pH paper or litmus paper color matches the NaOH’s test result. The reaction forms a pale blue precipitate, copper(II) hydroxide.
Skills: using indicator paper, measurement, making a solution, selection of appropriate glassware, selection of appropriate tools for measurement, and set up and use of an ice water bath
Conversion 3: Convert copper(II) hydroxide to copper(II) oxide
Students wash the blue precipitate with distilled water and heat the mixture to a gentle boil. The heat initiates the decomposition of the hydroxide compound forming a black, solid copper(II) oxide. When the oxide cools, students decant any remaining liquid and wash twice with distilled water.
Skills: measurement, using hot plates, and proper decanting
Conversion 4: Convert copper(II) oxide to copper(II) chloride
Students dilute a solution of hydrochloric acid to 6 M. The solution is poured over the copper(II) oxide causing an instantaneous change. The black sludge-like solid dissolves, leaving a crystal-clear green solution. Students love this conversion!
Skills: dilution and measurement
Conversion 5: Convert copper(II) chloride to copper
Students add small amounts of aluminum to displace the copper from solution. As the solution returns to a colorless liquid, students remove any unreacted aluminum and decant the fluid. The resulting copper is washed with distilled water and transferred to a watch glass. The product is dried in the drying oven and mass when cool and dry.
Skills: collection of product, use of drying oven, and measurement
A special thanks to Karen Heiges, our fellow AP chemistry teacher, who allowed me to share her work. Do you have a lab activity to share? Please post ideas as we finish this AP year and begin looking ahead. Do you have ideas for adding particle-level modeling to the lab? I look forward to reading your thoughts!