PURPOSE

The purpose of this experiment is to

• Run a series of redox reactions and record observations.

• Create an activity series for various metals.

INTRODUCTION

Redox reactions (oxidation-reduction reactions) occur when electrons are transferred between reactants. In these reactions, one species is oxidized (or loses electrons), and another is reduced (or gains electrons). (Note: In future chemistry courses, you will be exploring additional definitions of oxidation and reduction.) One way to identify oxidation is to observe when the charge on an atom increases or becomes more positive. In the following reaction

Na → Na⁺ + e^-,

sodium would be oxidized because the charge increases from 0 on the left to +1 on the right. In a reduction, the charge on an atom decreases, or becomes more negative, as shown in the example below:

Zn⁺² + 2e^- → Zn

In this experiment, we will explore redox reactions in which a metal is placed in an aqueous solution containing other metal ions. These reactions will take the following form:

2 Li (s) + MgCl₂ (aq) → 2 LiCl (aq) + Mg (s)

In these types of reactions, the solid metal is oxidized, and the metal in aqueous solution is reduced. Referring to the above example, Li is oxidized, and Mg is reduced. These reactions are also known as single replacement reactions because the metals are switching places.

As you will see from this experiment, not all these reactions will occur because some metals are more reactive than others. The reactivity of metals can be summarized in an activity series, which lists metals in order of increasing reactivity. More reactive metals are listed at the top of the series, and fewer reactive metals are listed at the bottom. For example, consider an activity series of generic metals A, B, C, X, Y, and Z.

B

C

Z

X

A

Y

According to this activity series, B would be the most reactive metal, and Y would be the least reactive metal. If we placed metal B in a solution containing C ions, a reaction would occur. Also, if we placed metal Z in a solution containing Y ions, a reaction would occur. However, no reaction would occur if metal A were placed in a solution containing B ions because B is more reactive than A. So, in summary, a reaction will occur if a metal is placed in a solution containing ions of a metal listed below it in the activity series.

Now, consider the following data concerning the reactions of Li, Ca, Na, and Mg:

According to experimental results, Li is the most reactive metal, and Mg is the least reactive metal. Based on this data, the following activity series may be created:

Li

Ca

Na

Mg

During this experiment, you will place metals in solutions containing various metal ions. You will be asked to record observations of reactions that occur. If a reaction does not occur, you will write NR (no reaction) in the data table. Then, based on the results of this experiment, you will create an activity series listing the metals explored from most to least reactive.

SAFETY PRECAUTIONS

1) Always wear safety goggles when working with chemicals in this experiment.

2) It is advisable to wear gloves when working with chemicals in this experiment.

3) Be sure to thoroughly read labels on reagent bottles to ensure the correct chemicals are always used.

4) Dispose of all waste, as directed by your instructor.

5) Thoroughly clean all glassware, equipment, and your work area when finished working on this experiment.

EXPERIMENTAL PROCEDURE

1) Cut four small strips of Mg (s) and place them into four separate medium size test tubes. Place the test tubes in a test tube rack. Cautiously and slowly add 5-10 mL of the following solutions to each test tube:

Test tube 1: zinc solution

Test tube 2: lead solution

Test tube 3: copper solution

Test tube 4: 1 M HCl

Let the reactions proceed for approximately 10 minutes. Then, record your observations in the data table. If a reaction did not occur, record this as NR in the data table. Discard the waste into the inorganic waste container, clean and dry your test tubes, and save them for the next step.

2) Repeat step 1 using Zn (s) instead of Mg (s) and replacing the zinc solution in test tube 1 with the magnesium solution.

3) Repeat step 1 using Pb (s) instead of Mg (s) and replacing the lead solution in test tube 2 with the magnesium solution.

4) Repeat step 1 using Cu (s) instead of Mg (s) and replacing the copper solution in test tube 3 with the magnesium solution.

5) Thoroughly clean all glassware and equipment and return them to the appropriate place.

6) Clean your work area before leaving the lab.

PRE-LAB QUESTIONS Name ____________________________________

1) In your own words, define oxidation and reduction.

2) True or false: Oxidation always occurs with reduction. The two cannot happen independently.

3) Based on the activity series in the introduction, would you expect the following reactions to occur? Why or why not?

Reaction 1: Ca (s) + 2 LiCl (aq) → CaCl₂ (aq) + 2 Li (s)

Reaction 2: 2 Na (s) + MgCl₂ (aq) → 2 NaCl (aq) + Mg (s)

Reaction 3: Mg (s) + 2 LiCl (aq) → MgCl₂ (aq) + 2 Li (s)

DATA AND OBSERVATIONS

Complete the following data table by recording your observations. For reactions that did not occur, write NR.

POST-LAB QUESTIONS

1) Based on the information provided in the data table, write an activity series for Cu, H, Mg, Pb, and Zn. (For more details, see the activity series presented in the introduction.)

2) Circle the best response.

For the reactions that occurred during this experiment, the solid metal was (oxidized/reduced) and the metal in aqueous solution was (oxidized/reduced).

3) Refer to the activity series you created in post-lab question 1 and predict whether the following reactions would occur as written.

Cu (s) + MgBr₂ (aq) → CuBr₂ (aq) + Mg (s)

Pb (s) + 2 HNO₃ (aq) → Pb(NO₃)₂ (aq) + H₂ (g)

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

4) Provide five examples of redox reactions that occur in everyday life.