Electrochemistry Galvanic Cell Lab PDF

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Galvanic Cell Lab SCH4U3 Dr. Sinclair December 12th, 2018

Purpose: To create a battery from pennies and zinc and to explore the effect of different factors on the of the battery.

washers voltage

Materials and apparatus: - 5 copper pennies - 5 zinc washers - Voltmeter - Wires - Solution of 1 mol/L NaCl - 5 filter paper discs - Watch glass - Tweezers Pre-Lab Questions: 1. What do you expect the direction of electron flow to be? The expected direction of electron flow would be from the anode to the cathode, from the zinc washer to the copper pennies. This is because zinc is more reactive than copper and more readily loses electrons. 2. What factors will determine how much voltage your battery can create? Brainstorm some variables you could investigate (at least 5 variables). Variables that could potentially determine how much voltage a battery can create are: a) The nature of the oxidizing and reducing agents (its strength) b) The concentrations of the electrolyte solution c) The temperature of the solution d) The number of cells in the battery e) The type of electrolyte solution used 3. Choose ONE of the above variables to investigate and predict how changes to this variable will affect voltage. Include how you would change your independent variable and how you will measure the dependent variable. If you need extra materials, please let your teacher know. The effect the number of cells has on the voltage will be investigated in this lab. The number of cells will be changed by stacking multiple cell units together, with opposite electrodes touching. Additional cells will be created and added to the battery one cell at a time. The dependent variable, which is the voltage created, will be measured using a voltmeter each time a new cell is added to the battery. Procedure: 1. At standard ambient temperature and pressure, 5 mL of 1 mol/L NaCl electrolyte solution was poured onto the wash disk and a piece of filter paper disc was placed in it until completely soaked. 2. The filter paper disc was placed on top of the zinc washer and the copper penny was placed on top of the filter paper disc. 3. A voltmeter was connected to the galvanic cell by connecting the negative side of the voltmeter to the zinc washer and the positive side to the copper penny using wires. 4. The voltage across the battery was measured and recorded. 5. Steps 1-4 were repeated three more times, adding a new cell to the top of the existing cells each time. Observations: Number of cells

Voltage across the battery (V)

1

0.40

2

0.60

3

0.80

4

1.00

5

1.20

Qualitative observations: After the experiment, some pennies which were quite bright and clean gained a layer of something dull, possibly oxidized, solid sodium

The number of Voltaic cells and voltage of the battery are directly proportional. As the number of cells in the battery increase, the voltage of the battery increases.

Discussion: Explain your observations with respect to galvanic cells and the electrochemistry theory. The voltage measured across a cell is the difference in voltage of each electrode, or the change in voltage from the anode to the cathode. Since the unit of voltage is joules per coulomb, the change in

voltage means the change in energy of a coulomb of charge. As a coulomb of charge goes through a single cell, its energy increases by the voltage of the cell. As it goes through the next cell, its energy increases again by the voltage of that cell. This means that the total change in energy is equal to the sum of the changes in energy of each cell and so the total change in voltage is equal to the sum of the changes in voltage of each cell. This means that the more cells you have, the higher the voltage of the battery. This is consistent with the observed results in this experiment.

State two sources of error for your investigation. Include a paragraph for each to discuss what the error was, the effect of the error on the lab and how you would change the procedure of the lab to minimize the error. 1. Source 1 - The lab equipment, specifically wires and voltmeters, did not all work well. The voltmeter may not have been the most accurate instrument to measure the voltage, because different groups found their data to be inconsistent or the voltmeter was simply not working. It was difficult to determine what the accurate voltages should be, because different groups were finding different voltages for similar conditions. This made it difficult to determine whether the data that was collected was accurate and how much of an effect the number of cells has on the voltage. To minimize this error, the voltmeters used should first measure the voltage of a previously known voltage, in order to test its accuracy. If the voltmeter is unable to display a correct reading, it will not be used in the experiment. 2. Source 2 - Copper and zinc contents are not distributed evenly on the surface of the coin/washer. Moving the contact point of the wire often results in very different voltage readings. This may be because that pennies are usually an alloy of metals instead of pure copper, or that the metal surface is corroded unevenly by the oxygen in the air. Since the distribution of copper is different in each coin, it was difficult to determine where the wire tip should be placed on the coin, resulting in inaccurate readings. To minimize this error, better materials that consist purely of zinc and copper should be chosen, and they should be rinsed in a slightly acidic solution before the experiment to clean the oxidized surface.

Extension Research:

Basic features and

Voltaic cell

Dry cell

Fuel cell

Electrolytic cell

Uses redox reactions of two electrodes that are

A type of galvanic cell where the

Energy is generated as reactants

An external energy source drives the non-

how each technology works

separated by a permeable layer soaked in an electrolyte

electrolyte is preserved in a paste

constantly flow into the cell

spontaneous redox reaction

Energy conversion

From chemical energy to electrical energy

From chemical energy to electrical energy

From chemical energy to electrical energy

From electrical energy to chemical energy

Common electrodes used

Zinc-copper, copper-silver

Zinc-carbon, mercury, lithium, nickel-cadmium

Usually hydrogen and oxygen gas

Nickel-cadmium, leadacid (PbO2 and lead metal)

Cost

Lowest

Lowest

Highest

$15-20 for the batteries, about $0.50 to charge

Applications

Button batteries, various types of batteries for small devices - hearing aids, pacemakers, flashlights

Small devices such as a remote control, bathroom scale, calculator

Cars and buses, space programs, the military, electric energy for homes

All rechargeable batteries behave as electrolytic cells; car batteries, portable devices

Corrosion may cause alkaline substances to leak, may explode if incinerated and release toxic heavy metals.

The only “waste” product is water and by far the cleanest energy source. However, the production of hydrogen gas as the fuel of the cell may release warmhouse gases and harmful substances.

Batteries that should be recycled may end up in landfills. Certain batteries may release toxic chemicals (eg. cadmium) which are hazardous to the environment and human health.

End-of life Vulnerable to corrosion. management Batteries are made of issues various materials, including many toxic heavy metals (eg. mercury, lead). If not disposed properly, its casing may disintegrate and the chemicals may leak into surrounding environment, contaminating soil and water.

Conclusion: From the results of this experiment, it can be concluded that an increase in the number of Voltaic cells causes an increase in the voltage of the battery. The number of cells is directly proportional to the voltage. As determined by other groups, and increase in temperature causes an increase in voltage, and an electrochemical cell produces the highest voltage when the electrolyte used contains a metal that is less reactive than its anode and has a lower reduction potential than its cathode. Other groups also determined that the concentration of the electrolyte does not have an effect on the voltage of the cell....