Learning Objectives
• Understand the relationship between the Ecell and a spontaneous reaction
• Understand the difference between a voltaic and electrolytic cell
• Use Le Chatelier’s principle to determine if an electrolytic/voltaic cell will be more or less spontaneous.
• Be able to quantify what happens to the anode and cathode (in terms of mass and concentration) in an electrochemical reaction.
• Be able to manipulate an electrochemical cell to achieve a desired voltage.
Why Study Electrochemistry?
Electrochemistry is the study of the relationships between chemical reactions and electricity. The functionality of every portable electronic device you own, whether it be your laptop, Ipod, or cell phone, is made possible by electrochemical reactions. Fundamental oxidation/reduction reactions occur inside the batteries of these devices. Chemists and engineers all over the world are searching for ways to improve the technology by developing materials which will make the batteries for these devices cheaper, more lightweight, and longer lasting.
Electrochemical reactions can be spontaneous or non-spontaneous. We will build on the principles we learned from the thermodynamics unit to determine if an electrochemical process is spontaneous. If it is not, we will learn how to manipulate electrochemical reactions to make them spontaneous.
Procedure Hints
Step #4: To prepare the electrodes you must wash them with acid. You can read the procedure below, or just watch the following video:
To prepare each electrode you must wash them with acid. If you are instructed to use a Cu, Sn, or Fe electrode, add about 20 mL of 3 M HCl to a 75-mL test tube. Immerse the electrode into the test tube and gently shake it for a few minutes. You can dispose the acid by dumping it down the drain. You will need to rinse the electrode by filling up the test tube half way with water. After it is rinsed, dump out the water and dry off the electrode with a Kimwipe. Your electrode is now good to go. If you are instructed to use Pb as an electrode, you will use a similar procedure, except you will need to use 3 M HNO3 instead of HCl and the acid wash must be properly disposed in the inorganic waste beaker. If you are using a Mg or Zn electrode add roughly 1 mL of 3 M HNO3 to a 25-mL test tube then fill it up with distilled water. Immerse the electrodes for about 5 seconds, rinse with distilled water, and blot them dry with a Kimwipe. The rinse solution for the Mg and Zn can be disposed down the drain.
Steps #7-8: The video below outlines steps 7-8, which shows how to properly use the Fluke Multi-meter
7. Now we are at the point where we can measure the potential difference. In order to do this you will be using a Fluke 175 Mutimeter, which you will need to connect properly. On the front panel of the Multimeter plug the black wire into the common ground (COM) position and the red wire into the voltage (V) position. Obtain some emery paper from your TA and sand the inside of both alligator clips.
8. Attach the alligator clip connected to the black wire to the zinc electrode and the alligator clip attached to the red wire to the copper electrode. Turn the knob on the Multimeter to DC volts, which is indicated by a straight line above a dotted line on top of the capital letter V.
Step #9: Step 9 shows how the read out on the multimeter changes when the lead wires are interchanged.
9. After about 30 seconds record the voltage in your lab notebook. Switch the alligator clips on the zinc and copper electrodes and note any changes that take place in the voltage reading in your lab notebook.
Steps #15-20: The Nernst equation describes the cell potential under non-standard conditions. Steps #15-20 of this lab illustrate this and can be seen below.
Steps #27-29: The video below demonstrates how to properly set up the Fluke Multi-meter for the Electrolytic Cell Experiments
Steps #30-31: The electrolytic cell for the electrodes given to you by your TA is observed in steps 30-31, which are seen in the video below.
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