lab

Introduction

Procedure

Part I: Redox Reaction Investigations

1. With my tweezers I placed one piece each of copper metal (Cu (s)) and zinc metal (Zn (s)) on

the paper towel each a few centimeters from the other.

2. I than placed 2 drops of 1 M CuSO4 solution onto the top of the piece of Zn (s) and another 2 drops of 1 M ZnSO4 solution onto the top of the piece of Cu (s).

3. I sudied each of the solution-metal interfaces with my hand lens.

4. Next I looked at the piece of copper metal with ZnSO4 on it, I removed the ZnSO4 from the copper metal with a cotton swab and compared it to the copper surface with another copper piece. The non-spontaneous reaction, i.e.,

the redox reaction that did not occur, is:Cu (s) + Zn2+ ßà Cu2+ + Zn (s)

5. I dried the metal pieces as well as my work surface with paper towels and left the metal pieces on

the plastic surface.

Part II: A Small Scale Electrochemical Cell

1. For part II I set up a multimeter to measure DC voltage. (Set on 2V DC (or 2000 mV which equals 2V in

thousandths).

2. I than cut one piece of filter paper into an approximate 4 x 8 cm rectangle and place it onto the

plastic surface.

3. Next I placed a piece of Cu (s) and a piece of Zn (s) onto the filter

paper about 3 cm apart.

4. I delivered 2 drops of 1 M CuSO4 to the paper just at the edge of the copper metal so that the

solution soaks under the metal piece. Then I delivered 2 drops of 1 M ZnSO4 to the paper so that it soaks under the zinc metal piece. I repeated that w/ 2 drops 1 M KNO3 to the dry paper in between the wet circles. The KNO3 solution will spread and run into the part of the paper wet with CuSO4 and ZnSO4.

5. I switched the multimeter on and touched the red probe (positive terminal) to the piece of copper

metal and the black probe (negative terminal) to the piece of zinc metal.

6. I reversed the probes and recorded what happens to the sign and switch the meter off.

at which reduction occurs. The voltage read in Step G should is positive.

Part III: An Electrochemical Series from Cell Data

1. With one 9-cm filter paper I made a cell template similar to the template shown in the diagram

2. I wrote on each sector the atomic symbols of the metals as shown and placed the cutout paper onto your sheet of plastic.

3. I used my tweezers to transfer the appropriate metal pieces to each sector and make sure they

were arranged in the order.

4. I dropped 2 drops of the related metal ion solution onto the paper at the edge of each metal piece

so that each metal is contacting the solution

5. I next dropped a few drops of KNO3 salt bridge solution into the middle so that it soaks outwards and

contacts all the other wet areas.

7. I than switched the multimeter to measure DC voltage. I took a measurement with the red probe on

Mg(s) and the black on Cu (s).

8. I kept the red probe on Mg (s) and take measurements by moving the black probe around

the circle in a clockwise manner.

9. I did the same movement the red probe to Cu (s) and continue around with the black probe.

Electrochemical Cells and Cell Potentials

Peter Jeschofnig, Ph.D. Version 42-0153-00-01

Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Questions Part 1 A. What half-reactions (one a reduction, the other an oxidation) can be written for this redox reaction?

B. How many electrons are being transferred from Zn (s) to Cu2+?

C. Which is the reducing agent and which is the oxidizing agent in this reaction?

D. Why does the Cu (s) produced in the redox reaction look very different from the copper metal piece?

Questions Part 2

A. Switch the multimeter on and touch the red probe (positive terminal) to the piece of copper metal and the black probe (negative terminal) to the piece of zinc metal. Read and record the voltage. Don’t forget the sign! (Refers to Procedures Part II Step 7)

B. Reverse the probes. Record what happens to the sign and switch the meter off. (Refers to

Procedures Part II Step 8)

C. Write the half-reaction occurring at the anode, Zn (s). (Refers to Procedures Part II Step 9)

D. Write the half-reaction occurring at the cathode, Cu (s). (Refers to Procedures Part II Step 10)

Experiment

Electrochemical Cells and Cell Potentials

147