Introduction:
Chemical reactions involving the transfer of electrons from one reactant to another are called oxidation-reduction reactions or redox reactions. In a redox reaction, two half-reactions occur; one reactant gives up electrons (undergoes oxidation) and another reactant gains electrons (undergoes reduction).
Voltaic cell is a device in which a redox reaction spontaneously occurs and produces an electric current. In order for the transfer of electrons in a redox reaction to produce an electric current and be useful, the electrons are made to pass through an external electrically conducting wire instead of being directly transferred between the oxidizing and reducing agents.
A salt bridge must be used to avoid polarization of the electrodes by facilitating the circulation of ions from electrolyte. Each electrode is connected to the voltmeter by clips and wires. The voltmeter measures the voltage generated by the redox reaction. The voltage reading will be positive when the electrodes are connected properly for spontaneous reaction. A redox reaction occurs when the species with higher reduction potential is connected as the cathode.
Research Question: What is the effect of different concentration of negative terminal electrolyte on the potential difference in voltaic cell?
Hypothesis: The lower the concentration of negative terminal electrolyte, the higher the potential difference in voltaic cell.
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Variables:
Manipulated variable| Concentration of negative terminal electrolyte * Use zinc sulphate solution, ZnSO4 as the negative terminal electrolyte throughout the experiment * Use zinc sulphate solution, ZnSO4 of different concentration, 1.0M, 0.10M, 0.010M and 0.0010M * Measure 40g, 4g, 0.4g and 0.04g of zinc sulphate powder then mix it in distilled water respectively until all the salt are completely dissolves then pour the solution into volumetric flask and add water until it make up to 250ml.| Responding variable| Potential difference * Measure the potential difference with a voltmeter * Take readings of potential difference when using different concentration of zinc sulphate solution, ZnSO4| Fixed variable| Type of electrode * Use two electrodes of different type, copper and zinc * Use electrodes of the same size, 5cm x 1cmPositive terminal electrolyte * Use copper (II) sulphate solution, CuSO4 as the positive terminal electrolyte * Use the same concentration of 1.0M copper (II) sulphate solution, CuSO4 throughout the experimentType of salt bridge * Use the same type of salt bridge, NaNO3 throughout the experiment.|
Apparatus:
* 500ml beaker
* 100ml beaker
* 50ml beaker
* Voltmeter
* Connecting wires
* 100ml measuring cylinder
* Electronic balance
* Glass rod
* 250ml volumetric flask
* Meter rule
* Scissors
Materials:
* Copper (II) sulphate powder
* Zinc sulphate powder
* Sodium nitrate powder
* Cotton string
* 0.5mm copper sheet
* 0.5mm zinc sheet
* Paper towel
Diagram:
Copper (II) sulphate solution, CuSO4
5cm x 1cm copper sheet electrode
Voltmeter
5cm x 1cm zinc sheet electrode
V
Cotton string soaked with sodium nitrate, NaNO3
Zinc sulphate solution, ZnSO4
Copper (II) sulphate solution, CuSO4
5cm x 1cm copper sheet electrode
Voltmeter
5cm x 1cm zinc sheet electrode
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V
Cotton string soaked with sodium nitrate, NaNO3
Zinc sulphate solution, ZnSO4
Procedure:
Preparation of zinc sulphate solution
1. Weight out 40.00g, 4.00g, 0.40g and 0.04g of zinc sulphate powder then dissolve the powder into distilled water in 50ml beaker respectively. 2. Pour the zinc sulphate solution into 250ml volumetric flask saperately and label it. 3. Add distilled water into each volumetric flask until it makes up to 250ml. 4. Mix the solution well in each volumetric flask.
Preparation of salt bridge
5. Weight out 100g of sodium nitrate powder then dissolves the powder into distilled water in 50ml beaker. 6. Pour the sodium nitrate solution into 250ml volumetric flask then add distilled water until it makes up to 250ml. Mix the solution well. 7. Pour the solution into 500ml beaker then soak 15cm cotton string in the sodium nitrate solution.
Preparation of copper (II) sulphate solution
8. Weight out 40g of copper (II) sulphate powder then dissolves it into distilled water in 50ml beaker respectively. 9. Pour the copper (II) sulphate solution into 250ml volumetric flask then add distilled water until it makes up to 250ml. Mix the solution well.
Voltaic cell set up
10. Measure 70ml of zinc sulphate solution made up of 40.00g zinc sulphate powder and 70ml of copper (II) sulphate solution.
11. Pour both solutions into to different 100ml beakers.
12. Cut out 5cm x 1cm of copper sheet and zinc sheet.
13. Set up the apparatus as shown in the diagram.
14. Record the three readings of the voltmeter.
15. Repeat the experiment by replacing zinc sulphate solution made up of 40.00g zinc sulphate powder with zinc sulphate solution made up of 4.00g, 0.40g and 0.04g zinc sulphate powder.
Precautions:
1. Rinse the beaker and zinc rod with distilled water before adding zinc sulphate electrolyte of different concentration. 2. Gently blot the zinc electrode and beaker with paper towel before adding zinc sulphate electrolyte of different concentration. 3. Ensure that the cotton is properly soaked and absorbed the sodium nitrate solution, NaNO3. 4. Avoid contacting the skin and eyes with chemicals.
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