ESTABLISHING A DISPLACEMENT SERIES USING CONSUMER MATERIALS
In this activity the order of oxidation or displacement of five common metals will be determined.
The activity is suitable for both first and second-year courses. Five metals (copper, magnesium, lead, iron, and zinc) and solutions of four ions (Mg2+, Zn2+, Fe2+, and Cu2+) are examined. In most cases two reactions provide the student with good evidence that one substance lies above another in oxidizing (displacement) activity. In a second part of the experiment, the reactions between copper, iodine, and ammonia are examined.
The activity will probably require three lab periods if performed by students. One lab period might be sufficient for teacher demonstration.
Avoid skin contact with solutions of acids and bases; dilute solutions used in this experiment may cause irritation. Removal of the zinc casing from a battery should be done with caution and safety protection only by a teacher. Batteries contain caustic mixtures of chemicals. Use caution when heating the Fe2+ solution; follow the directions prescribed in the procedure. Some hydrogen might be evolved when certain metals are placed in acidic solutions; avoid open flames while doing this experiment. Iodine causes skin irritation and can produce stains on clothing or skin. Goggles must worn throughout this experiment.
All chemicals used in this experiment are available from consumer products.
- 0.1 M MgSO4 solution (dissolve 24.7 g MgSO4 · 7 H2O in distilled or deionized water and dilute to 1.0 liter)*
- 0.1 M FeSO4 solution (dissolve 15.2 g FeSO4 in distilled or deionized water and dilute to 1.0 liter)*
- Zn2+ solution (dissolve 2.0 g Zn in dilute HCl, followed by neutralization with NaOH)*
- 0.1 M CuSO4 solution (dissolve 25.0 g CuSO4 · 5H2O in distilled or deionized water and dilute to 1.0 liter)*
- dilute NaOH solution*
- dilute HCl solution*
- dilute NH3 solution*
- phenolphthalein indicator (1% in ethanol)
- test tubes
- test tube rack
- small containers for solutions
- medicine droppers
- hot plate
- Petri dish
- glass stirring rod
- 150-mL beakers
- copper metal - chore knob, copper wire, or copper tacks
- zinc metal - galvanized nails, dry cell battery casing
- lead metal - fishing sinkers
- iron metal - steel wool
- MgSO4 · 7H2O - Epsom salts
- FeSO4 - leaf restorer (available from garden shop)
- CuSO4 · 5H2O - root eater (available from garden shop)
- NaOH - lye
- HCl (dilute) - muriatic acid (28% HCl) can be diluted
- NH3 (dilute) - household ammonia
- iodine - tincture of iodine
Metal activity series
- Prepare ion solutions and filter if they appear cloudy.
- Prepare solution of the zinc ion by
- cutting up a battery casing into small pieces to accelerate the rate of the reaction,
- dissolving 2.00 grams of the casing in dilute HCl,
- neutralizing the solution with NaOH, using phenolphthalein as an indicator. (Note; Zn(OH)2 might precipitate; if so, add a drop or two of HCl to make it slightly acidic.)
Figure 1. MATRIX
- Pb, Mg, Cu, and Zn metals should be cleaned with steel wool immediately prior to use.
- Mix metals and solutions of metallic ions as desired for instructional purposes. A matrix (Figure 1) is provided for instructional purposes and for recording results.
- Some reactions are slow and require observation over several minutes (see Discussion).
- Fe2+ will require heating as follows:
- Place a Petri dish on a hot plate, but do not turn on the heat.
- Add the Fe2+ solution.
- Add all the metals to be tested.
- Finally, turn on the hot plate.
*require heat (see procedure)
*** react slowly
Solutions can be flushed down the drain with plenty of water. Waste containers should be set aside to collect solid materials. School or state policy should be followed for disposal of metal solids.
Figure 1 contains a summary of all possible reactions. The activity, according to ease of oxidation, is as follows:
- Add clean copper metal to iodine solution. Stopper and shake. Observe and record.
- Add ammonia to the product of the above reaction.
- Add ammonia to a solution of the Cu + ion.
- Compare the results of the two ammonia tests.
most easily oxidized | Mg> Zn> Fe> Pb> Cu | most easily reduced
It is suggested that, in a teacher-led demonstration, the course of the discussion determine which reactions are used. In many cases more than one reaction gives the same information. For example:
Mg(s) + Zn+2(aq) Zn(aq) + Mg2+(aq)
Mg2+(aq) + Zn(s) NR
Both reactions indicate that magnesium is more easily oxidized than zinc. Students will soon recognize that only one such reaction is necessary. The demonstration becomes a more effective learning tool when students get to logically choose which reactions they need.
It is also very important that the reaction between copper metal and iodine be done to connect the replacement ability of metals to the nonmetals (see Tips). First, the copper metal reacts with the iodine according to the equation:
Cu(s) + I2(alc) CuI2(s)
The formation of the white copper(II) iodide precipitate on the surface of the copper metal indicates this reaction has occurred. To prove that Cu2+ has actually been produced, aqueous ammonia is added to the product:
CuI2(s) + 4 NH3(aq) [Cu(NH3)4]2+(aq) + 2 I- (aq)
The resultant blue color of the complex ion indicates the presence of the copper(II) ion.
Metcalfe, H. C., Williams, J.E., and Castka, J.F.,Modern Chemistry, Holt, Rinehart and Winston, Publishers, New York, 1982, pp. 175, 493.
- No source of Pb2+ ions has been suggested. This should not affect the student's ability to complete the table. The reactions of the metals with lead ion can be predicted from other results.
- A copy of the matrix in which only potentials, ions, and metals are listed should be distributed to the students for use in recording results.
- The experiment is long; it is suggested that students divide up the work.
- First year students might encounter some difficulty in concluding that no reaction has taken place. They should be encouraged to wait several minutes before deciding whether a reaction has occurred. Some class discussion will probably be necessary.
- All reactions which involve iron can be assumed t0 involve the ferrous ion, Fe2+. No doubt some Fe3+ is formed when Fe is oxidized, but for simplicity this should be ignored at this point.
- If time allows, it is suggested that a replacement activity for the halogens be carried out.
- This work discusses activity series and oxidation potentials.
Zumdahl, S.S., Chemistry, D. C. Heath and Company, Lexington, MA, 1986, pp. 129, 718, and 830.
- Oxidation potentials and activity series are discussed in this work.
Submitted by Michael Bannon, Jean Crowley, Diana Doepken, Dan Holmquist, and Carolyn Morse
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281