A laboratory experiment in a pipette.
Emily Saunders, Department of Chemistry, Creighton University, Omaha,
68178 USA, Charlie DiSapio and Ray Hamilton, Greenwich High School,
CT 06830 USA
In the previous installment of this series (May 2002, pages 4-5), we described a laboratory activity in which powdered iron(III) oxide, placed inside a glass pipette, could be used to demonstrate both physical and chemical changes. In this article, we describe another microscale experiment suitable for high school and college students that takes place inside a glass pipette. The reaction uses copper wool such as that sold as a kitchen scrubber and 50-mL H2(g). In the first part, the oxidation reaction between copper and oxygen (from air) to form black copper(II) oxide readily takes place:
2 Cu(s) + O2(g) 2 CuO(s)
The CuO(s) can be quantitatively reduced back to copper with hydrogen gas:
CuO(s) + H2(g) Cu(s) + H2O(g)
In the second reaction, H2O(g) condenses to droplets that are detected along the pipette stem. This experiment can be completed within a 30-minute laboratory period. The pipette/Cu device may be reused many times. A possible objective for this experiment is to draw attention to the four fundamental types of substances — metals, ionic compounds, molecular compounds and network covalent compounds. Students will work with all four in this experiment. (Silicon dioxide, the predominant component of the glass pipette, is a network-covalent compound.)
Copper wool from a ChoreBoy inside the pipet before the reaction is started.
Copper(II) oxide, CuO, forms as air is passed through the pipette.
Chemicals and Equipment.2 (This equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), Micro Mole, and Fisher Scientific. Part numbers and links to their websites are provided.)
• two 60-mL plastic syringes with LuerLok fittings
• Latex syringe caps
• 2-cm length of Latex tubing, 1/8-inch (3.175 mm) ID
• small Bunsen burner
• glass Pasteur pipette
• wooden stick such as a kabob skewer to position the copper wool into the pipette
• ring stand and clamp
• Silicone oil or spray
• copper wool such as a ChoreBoy kitchen scrubbing pad
• hydrogen (made from 5-mL 2 M HCl, 0.1 g Mg ribbon, powder or turnings)
Figure. The pipette reaction chamber.
General Safety Precautions.
Always wear safety glasses. Gases in syringes may be under pressure and could spray liquid chemicals. Follow the instructions and use only the quantities suggested.
This laboratory activity is suitable for high school and university-level chemistry students.
We recommend lubricating the black rubber diaphragm of the plunger with silicone spray (available from hardware stores) or medium-grade silicone oil (Educational Innovations Number GAS-150)
Prepare a syringeful of hydrogen from 0.1 g Mg (powder, ribbon or turnings) and 3 ? 5 mL 2 M HCl(g). Detailed instructions can be found at our website3 or in our two microscale gas books.4, 5
Part 1. Connect an air-filled syringe to the pipette using a short length of latex tubing. Heat the Cu/pipette for 30 s and then slowly pass the air through the pipette. The copper will quickly turn black. The oxide coating is very thin but binds tightly to the surface of the copper metal.
Part 2. Connect the H2-filled syringe to the pipette using a short length of latex tubing. Heat the CuO/pipette and then slowly pass the hydrogen gas through the pipette. The black oxide will quickly convert to shiny metallic copper metal and will appear unchanged from its original form. Water droplets should appear inside the stem of the pipette. After all of the hydrogen has been passed through the pipette, remove the heat and allow the pipette to cool. If the copper cools in the presence of hydrogen, it will retain its shiny copper color.
Volume of air passed through the pipette (over the Cu):Part 2.
Time it took to pass the air through the pipette:
Record observations for the reaction between Cu and air:
Volume of hydrogen passed through the pipette (over the CuO):
Time it took to pass the hydrogen through the pipette:
Record observations for the reaction between CuO and H2:
Laboratory Report Questions.
1. Balance the equation for the reaction between Cu and O2.Part 2.
2. Why is it necessary to heat the Cu in order for it to react?
3. Balance the equation for the reaction between CuO and H2.General Questions.
4. Calculate the rate of hydrogen flow in mL/min.
5. Why is it necessary to heat the CuO in order for it to react? Sketch a reaction profile energy diagram for the reaction.
6. The four fundamental types of substances are: metals, ionic compounds, molecular compounds and network covalent compounds. In this experiment you encountered an example of each of these. Match the following substances with the four fundamental types of substances. (a) hydrogen; (b) copper; (c) copper(II) oxide; (d) water; and (e) silicon dioxide (the predominant component of the glass pipette)
7. List 2 - 3 properties of each of the fundamental types of substances and give an additional example of each.
8. Three of the four fundamental types of substances are almost always solids under standard conditions. Which type can be solid, liquid or gas under standard conditions?
Clean-up and Storage.
At the end of the experiments, clean all syringe parts (including the diaphragm), caps and tubing with soap and water. Rinse all parts with distilled water. Be careful with the small parts because they can easily be lost down the drain. Important: Store plunger out of barrel. The pipettes filled with Cu may be saved for future use or safely discarded in the trash.
Pictures of this reaction sequence appear at our website.3 It is also possible to download this experimental procedure, laboratory report, and questions from this site as a Microsoft Word file (Word 2000 for PC and Word 98 for Mac). The web-based document includes answers to the concept questions. (Download this file.)
1 Author to whom correspondence should be addressed. E-mail: email@example.com
2 The syringe and related equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), S17 Science Supplies, Micromole, Fisher Scientific, etc. Part numbers and links to their websites are provided at our microscale gas website (Endnote 3)
3 Website: http://mattson.creighton.edu/Microscale_Gas_Chemistry.html then click on 'Lab Experiments', then on 'Reactions between CuO and hydrogen'
4 The Chemistry of Gases, A Microscale Approach, Mattson, B. M., Anderson, M. P., Schwennsen, Cece, Flinn Scientific, 1999, ISBN #1-877991-54-6.
5 Microscale Gas Chemistry, Mattson, B. M., Educational Innovations, 2000, ISBN #0-9701077-0-6.
Last updated 1 Feb