Report PDF

Preview

Summary

Report...

Description

Lab Report Electrochemistry 1 - Galvanic Cells

Introduction A cell capable of producing electrical energy from a chemical reaction, a redox reaction that occurs within it. The two half reactions are physically separated. The electrons transferred must pass through an external wire rather than being transferred by direct contact. Also bridge is also needed Galvanic cells are spontaneous chemical reactions that allow the conversion of chemical energy into Electric energy. It consists of two half cells each containing an electrode in an electrolyte solution oxidation occurs in 1 half cell and reduction in the other. The electorate of physically separated but connected by an external Circuit for the transfer of electrons from anode to the cathode. This flow of electrons produces electricity. In any commercial galvanic cells, the two Active chemicals must not be allowed to come in contact otherwise they would react directly and no electricity would be produced. The role of the electrolyte in cells is to keep the active chemicals apart while allowing migration of ions through the cells The reaction would not occur if the half cells did not remain neutral. Electrons are released by the oxidation reaction at the anode and pass along with external wire to the cathode where they are accepted by the species being reduced. A voltmeter can be connected in the wire to measure the voltage across two cells. Ions migrate along the salt bridge. All solutions in a galvanic cell electrolytes, including the solution in which electrodes are immersed and the solution that forms the salt bridge. Each galvanic cells can be considered to be a couple. Each half cell is made of a reactant and its oxidised or reduced product. Eg Zinc anode is placed in a zinc ion solution and is represented as Zn/Zn 2+. If it's connected to a copper cathode in a copper ion solution Cu/Cu2+. The whole cell can be represented as Zn/Zn2+// Cu/Cu2+. The single line denotes a change in phase (metal contact with solution), and the double line denotes a salt bridge. The two electrodes used must be of different metals or substances, so that there is potential difference between them. The two electrodes must be physically separated in solution otherwise the electrons will simply flow from one electrode to another direct, and there will be no voltage in the external circuit. The different voltage can be assigned to each half cell. These are called half cell potentials and are a measure of the relative tendency of the more oxidised form of the couple to gain electrons and are therefore called reduction potential. The EMF or voltage of the galvanic cell is the difference in the potentials of two half cells. The reduction potentials are relative to the H+/H2 half cells.

Aim identifying a group of unknown metals based on their reactivity, using the activity series and construct galvanic cells to measure the potential difference Hypothesis Combining Lead and Copper will produce the highest voltage Materials

-

3 250 ml beakers 3 salt bridge and 0.1M KNO3 0.1M ZnSO4 0.1M CuSO4 0.1M PbSO4 Zinc metal electrode Copper metal electrode Lead metal electrode 2 jumper wire with alligator clip at both ends Voltmeter

Method The Zinc, Copper and Lead plated were first rubbed with a sheet of sandpaper to remove all the rust it contained. The 3 250 ml beakers were half filled with 0.1M of ZnSO4(aq), CuSO4(aq), PbSO4(aq) solution and labeled accordingly. The first two couple were taken. Zn and Copper plates after cleaning were immersed in solutions of ZnSO4(aq) and CuSO4(aq) which were in the two beakers. A strip of filter paper was soaked in saturated 0.1M of KNO3(aq) and its ends

were placed in the solutions, creating a salt bridge. The digital voltmeter was then connected across the 2 electrodes with the 2 jumper wire with alligator clip attached to the metal plates. The measure voltage was then recorded in the table. Zn2+/Zn(s)//Cu2+/Cu(s)

The second two couple were taken. Zn and Lead plates after cleaning were immersed in solutions of ZnSO4(aq) and PbSO4(aq). Another strip of filter paper was soaked in saturated 0.1M of KNO3(aq) and its ends were placed in the solutions, creating a salt bridge. The digital voltmeter was then connected across the 2 electrodes with the 2 jumper wire with alligator clip attached to the metal plates. The measure voltage was then recorded in the table. Zn2+/Zn(s)//Pb2+/Pb(s)

The third and last two couple were taken. Copper and Lead plates after cleaning were immersed in solutions of ZnSO4(aq) and PbSO4(aq) Another strip of filter paper was soaked in saturated 0.1M of KNO3(aq) and its ends were placed in the solutions, creating a salt bridge. The digital voltmeter was then connected across the 2 electrodes with the 2 jumper wire with alligator clip attached to the metal plates. The measure voltage was then recorded in the table. Cu2+/Cu(s) and Pb2+/Pb(s)

Risk assessment Semi-micro test tubes must never be heated in a direct flame, lest the solution boils and erupts explosively. They must be placed in a beaker of boiling water instead. Bunsen burners present fire and burn hazards Heavy metals should be discarded appropriately and the solutions shouldn’t be dispossessed in the sink as it can cause a clog and can cause a serious chemical explosion.

Results

Metals used in Galvanic Cell

Zinc - Copper

Zinc - Lead

Copper - Lead

Measured voltage (V)

1.03

0.58

0.47

Result table shows that Zinc and Copper couple produced the highest voltage

Discussion

Conclusion

References...