Introduction

In class we will talk about electrochemistry, electrochemical cells and how cell voltages change in non-standard conditions. In this project you will have a chance to put this theory into practice and discover how well the experimental results follow the theory. The project will be split into several parts in which you will study the behavior of electrochemical cells. For each part you should have a hypothesis based on your knowledge of the theory or by reviewing the literature. After completing the project you should have a thorough enough understanding of electrochemical cells to make a cell of an assigned voltage. This will be the challenge that will count as part of your final exam grade.

You will be provided with:

Filter paper:

1M KNO₃ solution

0.1M Cu²⁺ solution

0.1M Zn²⁺ solution

0.1M Fe²⁺ solution

Iron nails

Strips of copper

Strips of Zinc

A CBL voltmeter

Wires and crocodile clips

Hot plate and ice bath
 
 

Part 1- The voltage of cells

Construct the following cells, using 50 ml beakers, metal electrodes and 0.1M solutions:

Zn/Zn²⁺ and Cu/Cu²⁺

Zn/Zn²⁺ and Fe/Fe²⁺

Cu/Cu²⁺ and Fe/Fe²⁺

Connect the 2 solutions together using a strip of filter paper soaked in KNO₃ to make a salt bridge and measure the voltage using a CBL system.
 

Hypothesis: Are your measured voltages close to the theoretically predicted values?
 
 

Part 2: Non-Standard Conditions

In theory, we can predict the voltage of a cell in non-standard conditions using the Nernst Equation:

E = E^o – (RT/nF)lnQ

Where R is the gas constant, F is the Faraday constant, n is the number of electrons transferred, E^o is the standard cell potential and Q is the reaction quotient.

According to this equation the only variables that could be used to change the cell voltage for a given cell are temperature and concentrations (to change the value of Q). We use this equation often in general chemistry but how well does it fit real experimental results?

Using one of your cells, investigate the effect of changing solution concentrations and temperatures. The design of these experiments is up to you. If your results follow the theory, is there a way of plotting your data to produce a straight line? Would the slopes or intercepts of these graphs have any meaning? Think about the best way to clearly present your results.

Hypothesis: This part will have 2 hypotheses based on the theory:

How do you expect cell voltage and solution concentrations to be related?

How do you expect temperature and cell voltage to be related?
 
 

Part 3: Combining cells

There is a good chance that the voltage you are given in the challenge will be significantly different from the possible voltage of any one cell. You will, therefore, have to know how to combine cells. There are 2 possible ways to connect your 2 cells, construct each one and measure the voltage. What happens to the voltage in each case? If time allows, try three cells.

Hypothesis: What do you expect the voltage to be when cells are combined
 
 

Assignment

At this point you are ready to write a journal article based on your results. Remember to discuss each part of the project. Include a hypothesis for each part of the experiment. Present your data clearly and discuss any differences between your hypothesis and your results for each part.
 
 

The Challenge

This is not part of the project and should not be included in the journal article. Your challenge is to construct a cell or combination of cells to achieve a voltage that will be assigned to you by your instructor. If you did a good job of investigating the electrochemical cell for the project and have your results clearly presented, the challenge should be straightforward. You will be graded on how close you came to the assigned voltage. The grade will be counted towards your final exam grade for this course.