Designing an experiment to investigate factors affecting the voltage of an electrochemical cell
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Background information
Standard electrode potentials of half-cells are often called standard reduction potentials. Equilibrium half-reactions are thus written with reduction as the forward reaction. The two electrodes reacting in this experiment are copper electrode and silver electrode. The copper electrode is the positive electrode with respect to the Standard Hydrogen Electrode (S.H.E)
Cu2+aq+2e-⇋Cus ECu2+/Cuθ=+0.34V
The silver electrode is the positive electrode with respect to the S.H.E
Zns⇋Zn2+aq+2e- EAg+/Agθ=+0.8V
Thus adding the two half-equations gives the overall cell reaction.
Cu(s)+2Ag(aq)+→Cu(aq)2++2Ag(s)
ECellθ=ERedθ-EOxidθ
=0.8V-0.34V
=+0.46V
Aim of the experiment
Hypothesis
If the concentration of the silver ions increases while the concentration of copper ions is fixed, the voltage of the electrochemical cell whose electrodes are silver and copper will increase as well.
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Variables
Independent variable
Concentration of the copper ions
Dependent variable
Voltage of the electrochemical cell
Controlled variable
Temperature of the solutions
Distance between the electrodes
Size of the electrodes
Apparatus
5 pieces of 0.25cm×0.5cm metals : Cu and Ag
1.0moldm-3 Solution: CuNO32
Steel wool
Small pieces of filter paper to serve as the salt bridge
12-well spot plates
Alligator clips and wires
Voltmeter
Thermometer
Method
Before start the experiment, using a thermometer, measure the temperature of the room and make sure that is fixed as 24℃ throughout the experiment.
Start to set up electrochemical cell of 1.0moldm-3 of CuNO32 of and 2.0moldm-3 of AgNO3.
Obtain small strips of filter paper, to be used as salt bridges.
Soak each strip with 1.0 moldm-3 of KNO3. Make sure the strip is entirely wet. Any dry patches will inhibit the flow of ions through the bridge.
Insert one end of the salt bridge into the zinc compartment and the other end into the copper compartment.
Attach the alligator clip from the negative terminal of the voltmeter to one of the metal electrodes and attach the second clip from the positive terminal to a different metal electrode in order to complete the external circuit.
10.If the voltmeter has a negative voltage, reverse the hook-up so that each clip is now attached to the other metal in the pair.
11.Record the voltage of the Voltaic/Galvanic cell for the reaction occurring at each electrode.
12.Repeat the process for 4 times with the remaining different concentrations of the AgNO3 which are 3.0, 4.0, 5.0, and 6.0moldm-3.
13.
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