Experiment 8: Electrochemistry
Required reading: E
ing, 11th Edition Chapter19.
Half reactions
Construction and notation for voltaic cells
Standard reduction potentials
Electroplating
Stoichiometry of electrolysis
Learning Goals:
To understand how to set up and work with an electrolytic cell.
To understand the concept of electroplating.
To predict mass of the metal from the solid deposited on one electrode of the electrolytic cell at a given time.
Background information and theory :
Chemical reactions where electrons are transfe
ed directly between molecules and/or atoms are called oxidation
eduction or redox reactions.Electrochemistry is the
anch of physical chemistry that studies the relationship between electricity, as a measurable and quantitative phenomenon, and identifiable chemical change, with either electricity considered an outcome of a chemical change or simply the reason for a chemical change to occur.When a chemical reaction is caused by an externally supplied cu
ent, it is known as electrolytic reaction. An electrolytic cell (figure 1) is an electrochemical cell in which an electric cu
ent drives a reaction. The process of producing a chemical change in an electrolytic cell is called electrolysis.
Figure 1. General description
of an electrolytic cell.The reactions ca
ied out in electrolytic cells are, under other conditions, non-spontaneous redox reactions. These can occur in an electrolytic cell because they use the electrical energy provided by a power source to occur.
On the contrary, other redox reactions would occur spontaneously and therefore would produce an electrical cu
ent, as it is the case of those taking place inside batteries. All these are, in general, refe
ed to as electrochemical reactions. In general, electrochemistry describes the overall reactions when individual redox reactions are separate but connected by an external electric circuit and an intervening electrolyte. Electrochemical cells have two conductive electrodes (the anode and the cathode). The anode is defined as the electrode where oxidation occurs, and the cathode isthe electrode where the reduction takes place. Electrodes can be made from any sufficiently conductive materials, such as metals, semiconductors, graphite, and even conductive polymers. In between these electrodes is the electrolyte, which contains ions that can freely move in an aqueous medium.The English physicist Michael Faraday showed that the total charge that flows in a circuit is related to the amount of substance released at the electrodes.
Electric charge = cu
ent × timeor written with co
esponding symbols and units (in parentheses)
Q (C) = I (A) × t (s)Where C is the symbol for Coulomb, A is ampere and s is seconds.In these types of calculations, it is typically useful to remember the Faraday constant (F), which says that one mole of electrons is equivalent to 96,485 coulombs of charge (F =
96,485 C/mol e-).
Procedure :
Part 1. The Simulation1. Watch the following video and complete the data table 1 and calculations for Part 1. If possible, use a split screen so that you can watch the experiment as you collect the data electronically. Alternatively, your instructor may give you instructions to print the data tables to complete them by hand as you watch the video. Watch as many times as you need: https:
www.youtube.com/watch?v=biycGsChyMc2. In the first part of this video, the electrolytic cell is set up for two Copper electrodes; one as anode and another one as cathode. Please use this part to understand the electrolytic cell set up and how it works. 3. Make sure to show your calculations in the space provided under the table 1.
Part 2. ElectroplatingIn the second part of this experiment, you will do the experiment using the simulation.
https:
www.youtube.com/watch?v=biycGsChyMc
1. Go to Electrochemistry Simulation.2. Under the experiment tab, select “Run Experiment”.3. Construct a zinc electroplating cell by choosing the following electrodes and solution: a. Anode: zincb. Cathode: iron c. Solution of Zn2+ ions.
Note: remember that in an electrolytic cell the charges are opposite to what they are
in a voltaic cell. 4. Record the initial mass of each electrode in the data table 2.5. Set the experimental conditions using a cu
ent of 2.00 amperes at 6.00 V for 5:00 minutes. 6. Run the simulation by clicking the ON/OFF switch.7. Fill out all data tables for part 2.8. Show your calculations under the table.
Part 3. Qualitative Analysis and Critical ThinkingIn the third part of this experiment, you will analyze the experiment using the simulation. You will need to be very detail oriented in this section in order to answer co
ectly all the co
esponding questions.
KEY NOTES:
Attention to detail is a critical skill in science. Whether you are reading quantitative
information (numerical), qualitative information (physical changes or lack there of),
or even just choosing the co
ect word to express something. Being careful with details
could lead to co
ect experimental results or successfully communicating experimental
esults or ideas.
Being detailed oriented does not mean we should take notes of everything we see, but
more about being able to point out the relevant details about a given experiment.
Generally, repeating a given experiment helps identify the relevant aspects of it. For
example, noting that the DC ammeter is gray might not be relevant for your
experiment. On the other hand, details like the color of the electrodes, or the solution,
or even if the applied cu
ent remains constant or not; could definitely be worthy of
tracking because they are directly related to your system, which in this case is the
electrolytical cell.
1. Click on “Reset” or reload the Electrochemistry Simulation as done in part 2.2. Construct a copper electroplating cell as follows a. Anode: Cu
https:
media.pearsoncmg.com
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c_0media_chem/chem_sim/html5/Electro/Electro.php
https:
media.pearsoncmg.com
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. Cathode: Ag c. Solution of Cu2+ ions. 3. Record every initial observation that you may consider relevant under part 3 of the data sheet.4. Set the following experimental conditions: a. Cu
ent = 2.00 A b. Voltage = 6.00 V c. Time = 30:00 min 5. Run the simulation by clicking the ON/OFF switch.6. Record every final observation that you may consider relevant under part 3 of the data sheet.7. Answer the questions in part 3 of the data sheet.
Name: ____________________________________
Electrochemistry
Data Sheet :Complete the following tables and indicate co
ect units when needed (parentheses). Additionally, answer the questions in part 3.
Part 1. The Simulation
Table 1. Simulation dataHalf reaction equation in cathodeHalf reaction equation in anodeInitial mass of cathode electrode XXXXXXXXXXInitial mass of anode electrode XXXXXXXXXXElectrical cu
ent XXXXXXXXXXNumber of coulombs passed after 10 min
Calculations:
Part 2. Electroplating
Table 2. Electroplating dataInitial mass of cathode electrode (Fe)Initial mass of anode electrode (Zn)Final mass of cathodeMass of zinc deposited on cathode ( )
Table 3. Chemical equations
Half reaction in CathodeHalf reaction in AnodeOverall Cell Reaction
Table 4. Calculated valuesStandard Cell Potential , Ecell°(E°cell = E°cathode – E°anode)Number of coulombs after 5 min(Coulombs = cu
ent x time)Number of Faradays (F = no. of Coulombs / 96,500)Final Mass of Cathode after 5 min
Calculations:
Part 3. Qualitative and Critical thinking
Observations:
1. Thinking about the section of the electrodes shown above the solution, did you observe any changes? If so, what were these?
2. Thinking about the section of the electrodes shown below the solution, did you observe any changes? If so, what were these?
3. You should have observed a decrease on the mass of the copper electrode. a. What happened to that copper? Did it disappear? Where did it go?
. What visual evidence can you use to support your previous answer (3a)?
4. Go back to the simulation page and try to set up a version of the electrolytic cell from part 3 but with inverted electrodes (that is anode = Ag, cathode = Cu and Ag+ solution).a. Is that possible?
. why?
Name: ____________________________________
Electrochemistry
Prelab Questions :
1. Balance the following oxidation–reduction equations.a. ??2?72- + ?2?2 → ??3+ + ?2 ( )?????? ????????
. Cr (OH )4−¿+OCl−¿→CrO 42−¿+Cl−¿¿¿¿¿ ( )????? ????????
2. A silver oxide-zinc cell maintains a fairly constant voltage during discharge (1.60V). The button form of this cell is used in watches, hearing aids, and other electronic devices. The half-reactions are:
Zn ( s)+2OH−¿ ( aq)→Zn (OH )2 ( s)+2e
−¿ ¿¿
Ag2O (s )+H2O (l )+2e
−¿→2 Ag ( s)+2OH−¿( aq)¿ ¿Identify the anode and the cathode reactions. What is the overall reaction in this voltaic cell?
Name: ____________________________________
Electrochemistry
Post Lab Questions :The following questions are all about part 2 of this experiment.1. Is electroplating a spontaneous reaction, or does it require energy? (Look at the voltage)
2. What attracts the Zn onto the Fe electrode?
3. State the direction of electron flow through the circuit.
4. Calculate the moles of zinc formed.
5. Write the Zn half reaction that takes place on the Fe electrode as Zn is deposited.
6. How many moles of electrons are transfe
ed when one mole of Zn is formed?
Feedback BlockDid you find any typos in this experiment? Please report them here: Typos ReportDid you find any non-typo issues with it? (i.e. videos not working well,more space for calculations, etc.) Please report here: Content ReportDid you love the experiment? Let us know! Rate it here
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Experiment 8: Electrochemistry
Background information and theory:
Procedure:
Part 1. The Simulation
Part 2. Electroplating
Part 3. Qualitative Analysis and Critical Thinking
KEY NOTES:
Data Sheet:
Part 1. The Simulation
Part 2. Electroplating
Part 3. Qualitative and Critical thinking
Prelab Questions:
Post Lab Questions:
Feedback Block
Experiment 8: Electrochemistry
Required reading: E
ing, 11th Edition Chapter19.
Half reactions
Construction and notation for voltaic cells
Standard reduction potentials
Electroplating
Stoichiometry of electrolysis
Learning Goals:
To understand how to set up and work with an electrolytic cell.
To understand the concept of electroplating.
To predict mass of the metal from the solid deposited on one electrode of the electrolytic cell at a given time.
Background information and theory :
Chemical reactions where electrons are transfe
ed directly between molecules and/or atoms are called oxidation
eduction or redox reactions.Electrochemistry is the
anch of physical chemistry that studies the relationship between electricity, as a measurable and quantitative phenomenon, and