Materials Included In Kit

Additional Materials Required

Prelab Preparation

Part 1. Determine an Activity Series for Metals

Each student needs four shiny pieces of each metal, each about 6 mm square. Polish with steel wool or fine grit sandpaper before cutting if needed. Approximately 4 mL of each metal nitrate solution is needed by each student group.

Part 2. Determine an Activity Series for Some Halogens 

Chlorine water, 50 mL: Work in a fume hood. Pour about 15 mL sodium hypochlorite solution into about 35 mL distilled water. Slowly, with stirring, add 5 mL of 6 M hydrochloric acid solution. The solution quickly turns pale yellow-green and bubbles as chlorine vapors are given off. Allow the solution to stand uncovered in a hood until the reaction stops. Pour the solution into the amber glass bottle labeled “chlorine water.” Place the provided black polypropylene cap on the labeled solution bottle. Because the chlorine is so volatile, the solution does not store well and should be used within one week of preparation. Each student group needs about 4 mL of solution.

Bromine water, 50 mL: Work in a fume hood. Wear gloves and goggles. Dissolve 1.1 g sodium bromide in 10.7 mL of 1 M hydrochloric acid. Place this solution in the amber glass bottle labeled “bromine water.” Add 7.6 mL of sodium hypochlorite solution to the bottle. Swirl gently to mix. Dilute with 32 mL of distilled or deionized water. Place the provided black polypropylene cap on the labeled bottle. This solution has a poor shelf life and should be used within one week of preparation. Each student group needs about 4 mL of solution.

Iodine water, 50 mL: Add about 0.3 g solid iodine plus 50 mL of distilled water to the amber glass bottle labeled “iodine water.” Swirl to mix. Some solid iodine may remain at the bottom of the solution. Prepare at least one day before using as iodine dissolves very slowly in water. The solution has a poor shelf life and should be used within one week of preparation. Each student group needs about 4 mL of solution.

Halide solutions and mineral oil: Approximately 12 mL of mineral oil and 4 mL of each halide solution are needed by each student group.

Safety Precautions

The silver nitrate solution is moderately toxic by ingestion and is a body tissue irritant. Silver nitrate stains skin and clothing; however, the stains may not appear for several hours. The copper(II) nitrate solution is slightly toxic by ingestion and is irritating to skin, eyes and mucous membranes. Zinc nitrate solution is slightly toxic by ingestion and is corrosive to body tissue. Magnesium nitrate solution is a body tissue irritant. The lead nitrate solution is moderately toxic by ingestion and inhalation; it is a possible carcinogen and is irritating to skin, eyes and mucous membranes. The magnesium ribbon is a flammable solid. The sodium hypochlorite solution is moderately toxic by ingestion and inhalation; it is corrosive to body tissue and reacts with acids to generate toxic chlorine gas. Sodium bromide solid is slightly toxic by ingestion and inhalation; it is irritating to body tissue. Both hydrochloric acid solutions are toxic by ingestion and inhalation. They are severe corrosives to body tissue, especially skin and eyes. Iodine solid is highly toxic by ingestion and inhalation. It is irritating and corrosive to skin. In this lab, sodium hypochlorite is reacted with hydrochloric acid to generate small amounts of very dilute halogen solutions for use by the students. This step should only be performed by the teacher and in the amounts indicated. Follow the directions carefully and work in an operating fume hood. The chlorine, bromine and iodine water solutions have strong odors and are highly toxic by ingestion and inhalation. All are very irritating to eyes, skin and mucous membranes. Conduct this activity in a hood or well-ventilated lab only. Mineral oil is a combustible liquid. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please consult current Safety Data Sheets for additional safety information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Provide a container into which students can discard the solutions. Place crumpled aluminum foil in the container and allow it to stand for 24 hours. The silver, copper, and lead metals all precipitate out of solution, leaving essentially none of these ions dissolved. The solution can then be filtered and the solids may be disposed of according to Flinn Suggested Disposal Procedure #26a. The solution may be disposed of according to Flinn Suggested Disposal Procedure #26b. Clean the 24-well plate with detergent and water using cotton swabs if needed. Provide a container into which students can empty their test tubes. Use a different container from the one used in Part 1. Place this container in the hood for several days during which time the chlorine will evaporate from solution. The remaining solution may then be disposed of according to Flinn Suggested Disposal Method #12a. Chlorine water may be disposed of in a similar fashion, except the remaining solution may be disposed of according to Flinn Suggested Disposal Method #26b. Bromine and iodine water solutions may be disposed of according to Flinn Suggested Disposal Method #12a.

Lab Hints

Part 1

• To reduce the number of Beral pipets used, attach a small test tube to each solution bottle and place a pipet in each test tube. The students can then share the pipet. Alternatively, the solutions can be placed in dropping bottles.
• To reduce the number of test tubes used in Part 2, one set of six test tubes, referencing the colors of the three halogens and the three halide solutions in mineral oil, can be used by the entire class.
• Caution students about the toxicity of lead and silver compounds, and the effect of silver solutions causing stains. A silver polish like Tarnex^® will help remove some stains caused by silver solutions.
• Students should observe the metal surface to determine if a reaction occurred. A stirring rod should be used to submerge the metal pieces in the solutions. If metal “A” reacts with ion “B,” then metal “B” should not react with ion “A.” Students should check combinations to be sure their data are consistent. Since silver metal is not used in the experiment, the reactivity of the silver ion in solution must be used to determine silver’s placement in the activity series.

Part 2

• Prior to lab, review with students the recommended safety precautions for working with halogens. Caution the students to never, ever sniff the halogen water solutions. Some students are tempted to do this with chlorine water, because it is colorless and the presence of chlorine is not obvious.
• The small amounts of chlorine and bromine water used in this experiment may be safely worked with at laboratory benches in a well-ventilated lab. If a hood is available, dispense the halogen water solutions in the hood. The students should stopper the halogen water tubes in the hood before carefully transferring them back to their lab benches. To avoid congestion when dispensing the reagents, stagger the starting points for steps 1 and 7. Half the student groups can start with step 1, the other half with step 7, then switch.
• Be sure that students understand the difference between a halogen (the neutral element dissolved in water, i.e., Br₂) and the halide (the ion of the halogen, i.e., Br^–). Students should observe that the halide ions do not give any color to the mineral oil layer, but the halogens do. Chlorine is colorless to slight yellow, bromine is orange, and iodine is pink or purple when dissolved in mineral oil. Students should look to see which halogen is dissolved in the mineral oil layer when deciding whether a reaction has occurred.

Teacher Tips

• Students are often stumped when no reaction is observed. They may lack the experience or confidence to state that no change has been observed. It may be helpful to keep a control set of test tubes from Part 2 on display in the hood. Sometimes a leading question may be helpful—what color would you expect if a reaction did occur?
• The discovery of fluorine is an interesting story. As students can infer from the results of Part 2, fluorine must be the most reactive of the halogens. In fact, it is the most reactive of all nonmetals—the strongest oxidizing agent known-and extremely poisonous. For these reasons, fluorine was the last of the halogens to be discovered in its free element form. Chlorine, bromine, and iodine had all been isolated as their free elements by 1830. The element fluorine, however, was not successfully prepared until 1886 by the French chemist Henri Moissan. In the period between 1830 and 1886, several scientists died in their unsuccessful attempts to prepare elemental fluorine, and many more scientists, including Moissan, suffered serious health effects due to fluorine poisoning.

Further Extensions

This lab fulfills the requirements for the College Board Recommended AP Experiment #20: Determination of Electrochemical Series.

Sample Data

Part 1. An Activity Series for Some Metals

Sample data from metal ions and metals:

Answers to Questions

1. Write balanced net ionic equations for all the reactions that occurred with the metals.

   2Ag⁺(aq) + Cu(s) → 2Ag(s) + Cu²⁺(aq)
   2Ag⁺(aq) + Mg(s) → 2Ag(s) + Mg²⁺(aq)
   2Ag⁺(aq) + Pb(s) → 2Ag(s) + Pb2+(aq)
   2Ag⁺(aq) + Zn(s) → 2Ag(s) + Zn²⁺(aq)
   Cu²⁺(aq) + Mg(s) → Cu(s) + Mg²⁺(aq)
   Cu²⁺(aq) + Pb(s) → Cu(s) + Pb²⁺(aq)
   Cu²⁺(aq) + Zn(s) → Cu(s) + Zn²⁺(aq)
   Pb²⁺(aq) + Mg(s) → Pb(s) + Mg²⁺(aq)
   Pb²⁺(aq) + Zn(s) → Pb(s) + Zn²⁺(aq)
   Zn²⁺(aq) + Mg(s) → Zn(s) + Mg²⁺(aq)

2. List the metals in order of decreasing ease of oxidation. Compare your list with an activity series found in a textbook. How do the two lists correlate?

   Most reactive to least reactive: Magnesium > Zinc > Lead > Copper > Silver
   The series agrees with that given in the textbook.

3. Write reduction half-reactions for each of the metal ions. Arrange the reaction list in order of decreasing ease of reduction. Compare your listing with a listing found in a table of standard reduction potentials. How do the two lists correlate?

   Ag⁺(aq) + e^– → Ag(s) E° = +0.799 V
   Cu²⁺(aq) + 2 e^– → Cu(s) E° = +0.337 V
   Pb²⁺(aq) + 2 e^– → Pb(s) E° = –0.126 V
   Zn²⁺(aq) + 2 e^– → Zn(s) E° = –0.763 V
   Mg²⁺(aq) + 2 e^– → Mg(s) E° = –2.37 V
   The order of the list agrees with the order for standard electrode potentials from most positive to most negative.

4. Explain how to determine if a reaction occurs in the halogen experiment.

   The color of the mineral oil layer indicates whether a reaction has occurred. If the color of the halogen placed in solution is present, no reaction has taken place. If the color of the halogen which was initially present as an ion appears, then the halide ion was oxidized to the halogen.

5. Why should the halide ions not dissolve in mineral oil?

   Since halide ions are charged particles and are thus polar, they will dissolve in the polar water but not in the nonpolar mineral oil.

6. Explain what is meant by solvent extraction. How is it used in Part 2?

   In solvent extraction, two immiscible liquids are shaken together. The more polar solutes dissolve preferentially in the more polar solvent, while the less polar solutes dissolve in the less polar solvent. In this experiment the nonpolar halogens preferentially dissolve in the nonpolar mineral oil.

7. Write balanced net ionic equations for the reactions which occurred with the halogens.

   Cl₂(aq) + 2Br^–(aq) → 2Cl^–(aq) + Br₂(aq)
   Cl₂(aq) + 2I^–(aq) → 2Cl^–(aq) + I₂(aq)
   Br₂(aq) + 2I^–(aq) → 2Br^–(aq) + I₂(aq)

8. List the halogens in decreasing order of reactivity. Compare this list with an activity series found in a textbook. How do the two lists correlate? Predict the location of fluorine in this activity series.

   Most reactive to least reactive: Chlorine > Bromine > Iodine
   The order does agree with values published in a textbook.
   The halogens become less reactive as atomic number increases. Fluorine has the smallest atomic number of the halogens and therefore should be the most reactive.

9. Write reduction half reactions for each of the halogens. Arrange in order of decreasing ease of reduction. Compare the listing with the order found in a table of standard reduction potentials. How do the lists correlate?

   Cl₂(g) + 2 e^– → 2Cl^–(aq) E° = +1.359 V
   Br₂(l) + 2 e^– → 2Br^–(aq) E° = +1.065 V
   I₂(s) + 2 e^– → 2I^–(aq) E° = +0.536 V

10. Why was it necessary to test the halide ions for their color in mineral oil?

    It was necessary to test the solutions of halide ions to be sure that they did not interfere with the colors observed from the halogens in mineral oil.

11. Would it make a difference if calcium bromide solution, CaBr₂, is used rather than sodium bromide solution? Explain.

    It would make no difference since both provide bromide ions, and the cations are spectator ions.

Introduction

In this experiment, a series of metals and a series of nonmetal halogens are studied to find their relative reactivities. The reactivity of the metals is determined by combining the metals with a complementary series of metal ions in solution. The reactivity of three halogens is found by mixing each with a halide ion solution. Using the observed reactions, an activity series, from most reactive to least reactive, is developed for the metals and for the halogens.

Concepts

• Activity series
• Oxidation–reduction
• Half-cell reaction

Background

A ranking of elements according to their reactivity is called an activity series. For example, an activity series containing the elements calcium, gold, and iron would put the reactive calcium at the top, iron in the middle, and the unreactive gold at the bottom. If a piece of iron metal is placed in a solution of gold nitrate, the iron dissolves forming positive ions in solution while solid gold metal appears. The more reactive metal (iron) displaces ions of the less reactive metal [gold(III)] from solution. The less reactive element appears as the solid element.

Reactions such as these are examples of oxidation–reduction reactions. Oxidation is defined as the process of losing electrons and substances that lose electrons during chemical reactions are said to be oxidized. Substances that gain electrons during chemical reactions undergo reduction and are said to be reduced. If one reactant gains electrons, another must lose electrons. Oxidation and reduction reactions occur simultaneously, and there must be an equal number of electrons lost and gained during the two reactions. In the reaction of iron metal with gold ions, the iron metal is oxidized and the gold ions are reduced. The more reactive metal is the one that is more easily oxidized.

When writing oxidation–reduction reactions, it is customary to break the reaction into the two parts or half-cell reactions. These half-cell reactions represent the separate oxidation and reduction processes that occur simultaneously. The electrons within the two half-cell reactions must be equal so there is no net gain or loss of electrons for the overall reaction.

When a substance readily loses electrons (and is oxidized), it acts as a good reducing agent. When a substance has a strong tendency to gain electrons (and be reduced), it acts as a good oxidizing agent. Gold ions, Au³⁺(aq), have a strong tendency to acquire electrons to form neutral gold atoms, Au(s). Gold ions are thus easily reduced and act as good oxidizing agents.

Experiment Overview

The purpose of this experiment is to determine the activity series for five metals and for three halogens. The first part of this experiment derives an activity series for metals and uses a microscale technique. The second part derives an activity series for halogens. It makes use of a solvent extraction technique.

The series of metals to be studied are copper, zinc, magnesium, lead and silver. Solutions of metal nitrates for each of these metals are placed in reaction wells. A piece of each metal is then placed in the other metals’ nitrate solutions and observed to see if any reaction occurs. If a metal reacts with another metal nitrate, then the solid metal has reduced the other metal ion and is, therefore, the more reactive metal of the two. By comparing the results of 16 different reactions, the five metals are ranked from most reactive to least reactive.

In Part 2, tests are performed to determine the activity series of the halogens. Chlorine (Cl₂), bromine (Br₂) and iodine (I₂) are placed in solutions containing chloride (Cl^–), bromide (Br^–) or iodide (I^–). An activity series of the nonmetallic halogens places the most reactive halogen at the top. In the reaction of a free halogen (X₂) with a different halide ions (Y^–), the free halogen gains electrons and is then reduced to its corresponding halide ions (X^–). The original halide ions lose electrons and therefore are oxidized to their corresponding free halogen (Y₂). The more reactive halogens displaces ions of the less reactive halides from solution. In an activity series of halogens, the most reactive halogen is the one most easily reduced.

To determine if a reaction occurs, a method is needed to identify which halogen is present. Halogens dissolve in the nonpolar solvent mineral oil forming different colored solutions. Mineral oil does not dissolve in water, but when shaken with an aqueous halogen solution, the halogen is extracted from the water into the mineral oil. The color of the mineral oil layer indicates which halogen is present.

Materials

Safety Precautions

The silver nitrate solution is moderately toxic by ingestion and is a body tissue irritant. Silver nitrate stains skin and clothing; however, the stains may not appear for several hours. The copper(II) nitrate solution is slightly toxic by ingestion and is irritating to skin, eyes and mucous membranes. Zinc nitrate solution is slightly toxic by ingestion and is corrosive to body tissue. Magnesium nitrate solution is a body tissue irritant. The lead nitrate solution is moderately toxic by ingestion and inhalation; it is a possible carcinogen and is irritating to skin, eyes and mucous membranes. The magnesium ribbon is a flammable solid. The chlorine, bromine and iodine water solutions have strong odors and are highly toxic by ingestion and inhalation. All are very irritating to eyes, skin and mucous membranes. Mineral oil is a combustible liquid. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part 1. Determine an Activity Series for Metals

1. Place the 24-well plate on top of a piece of white paper so that there are 6 wells across (columns) and 4 wells down (rows). Refer to Figure 3 to see how the wells are arranged. Note that each well is identified by an unique combination of a letter and a number, where the letter refers to a horizontal row and the number to a vertical column.
   {10536_Procedure_Figure_3}
2. Put one dropper-full (about 15 drops or 1 mL) of copper(II) nitrate solution in wells B1, C1 and D1 in the first column.
3. Put one dropper-full of magnesium nitrate solution in wells A2, C2 and D2 of the second column.
4. Put one dropper-full of lead nitrate solution in wells A3, B3 and D3 of the third column.
5. Put one dropper-full of zinc nitrate solution in wells A4, B4 and C4 of the fourth column.
6. Put one dropper-full of silver nitrate solution in each of the wells A5 through D5 in the fifth column.
7. Put a small piece of copper metal in each of the wells containing a solution in the first row.
8. Add magnesium metal to the solutions in the second row, add lead metal to the solutions in the third row, and add zinc metal to the solutions in the fourth row. Use a stirring rod to submerge each metal in the solutions. Allow to stand at least 5 minutes.
9. Determine if a reaction has occurred in each well by observing if a new metal has deposited or if the surface of the metal has become coated.
10. Record each observation as either coating forms or no reaction in the Part 1 Data Table.
11. Discard all solutions into the container provided by your instructor. Clean the 24-well plate with soap and water using cotton swabs if needed. A different container than the one used in Part 1 will be used in Part 2.

Part 2. Determine an Activity Series for Some Halogens

All work in Part 2 should be done in a fume hood.

1. As a reference, test to see what color develops when each halogen is dissolved in mineral oil. Place one dropper-full of chlorine water, one dropper-full of bromine water, and one dropper-full of iodine water into three separate 10 mm test tubes.
2. Add one dropper-full of mineral oil to each test tube, cork the tube, and shake it for ten seconds.
3. Let the mineral oil layer rise to the top and record the color that each halogen shows when dissolved in mineral oil. Record your observations in the Part 2 Data Table.
4. Test to see if the halide ions give a color to mineral oil. Place one dropper-full of sodium chloride, sodium bromide and potassium iodide solutions into three separate test tubes.
5. Add a dropper-full of mineral oil to each test tube, cork the tubes, and shake for ten seconds to determine if the halide ions impart a color to the mineral oil layer.
6. Record your observations in the Part 2 Data Table.
7. Set up six test tubes in a test tube holder as in Figure 4. Label the test tubes 1 through 6 with a marker.
   {10536_Procedure_Figure_4}
8. React each halogen with the other two halide ion solutions to determine if the ions reduce the halogens. Place one dropper-full of sodium bromide solution into test tube 1 and one dropper-full of potassium iodide solution into test tube 2.
9. Add one dropper-full of chlorine water to each of test tubes 1 and 2, cork each, and shake to mix.
10. Add one dropper-full of mineral oil to each of test tubes 1 and 2, cork each, and shake again.
11. When the mineral oil layer has separated, determine its color and whether a reaction has occurred. If the color of the chlorine appears in the mineral oil layer then no reaction has occurred. If either the bromine or iodine color appears in the mineral layer, then there was a reaction.
12. Record both the color and the reaction results (reaction or no reaction) for Cl₂(aq) in the Part 2 Reaction Data Table.
13. Repeat the test using bromine water. Add one dropper-full of sodium chloride solution to test tube 3 and one dropper-full of potassium iodide to test tube 4.
14. Add one dropper-full of bromine water to each of test tubes 3 and 4, cork each, and shake to mix.
15. Add one dropper-full of mineral oil to each of test tubes 3 and 4, cork each, and shake again.
16. When the mineral oil layer has separated, determine its color and whether a reaction has occurred. If the color of the bromine appears in the mineral layer, then no reaction has occurred. if either the chlorine or iodine color appears in the mineral layer, then there was a reaction.
17. Record both the color and reaction results (reaction or no reaction) for Br₂(aq) in the Part 2 Reaction Data Table.
18. Repeat the test for iodine water. Add one dropper-full of sodium chloride solution to test tube 5 and one dropper-full of sodium bromide solution to test tube 6.
19. Add one dropper-full of iodine water to each of test tubes 5 and 6, cork each, and shake to mix.
20. Add one dropper-full of mineral oil to each of test tubes 5 and 6, cork each, and shake again.
21. Record both the color of the mineral oil layer and the reaction results (reaction or no reaction) for I₂(aq) in the Part 2 Data Table.
22. Empty the test tubes in the container provided for disposal by your instructor. 

Student Worksheet PDF

10536_Student1.pdf