Figure 1 represents the cell used to measure the standard electrode potential for the Fe<sup>3+</sup>/Fe<sup>2+</sup> electrode - AQA - A-Level Chemistry - Question 3 - 2019 - Paper 3
Question 3
Figure 1 represents the cell used to measure the standard electrode potential for the Fe<sup>3+</sup>/Fe<sup>2+</sup> electrode.
03.1 Name the piece of apparatus la... show full transcript
Worked Solution & Example Answer:Figure 1 represents the cell used to measure the standard electrode potential for the Fe<sup>3+</sup>/Fe<sup>2+</sup> electrode - AQA - A-Level Chemistry - Question 3 - 2019 - Paper 3
Step 1
Name the piece of apparatus labelled A.
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Answer
The piece of apparatus labelled A is a salt bridge. It facilitates the flow of ions to maintain electrical neutrality in the electrochemical cell.
Step 2
State the purpose of A.
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The purpose of the salt bridge is to complete the circuit by allowing ionic flow between the two half-cells, which prevents charge buildup.
Step 3
Name the substance used as electrode B in Figure 1.
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Electrode B in Figure 1 is made of platinum (Pt), which is commonly used for its inertness and good conductivity in electrochemical cells.
Step 4
Complete Table 1 to identify C, D and E from Figure 1. Include the essential conditions for each.
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C - HCl, Conditions: 1 mol dm<sup>-3</sup> concentration
D - **H<sub>2</sub>, Conditions: 100 kPa pressure
E - **Fe<sup>3+</sup>/Fe<sup>2+</sup>, Conditions: 1 mol dm<sup>-3</sup> concentration
Step 5
Give the ionic equation for the overall reaction in Figure 1.
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The ionic equation for the overall reaction is:
ightarrow ext{Fe}^{2+}$$
Step 6
State the change that needs to be made to the apparatus in Figure 1 to allow the cell reaction to go to completion.
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To allow the cell reaction to go to completion, it is necessary to remove the Fe<sup>2+</sup> ions from the solution as they are produced.
Step 7
Complete Table 2 to show the value missing from experiment 4.
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For experiment 4, the missing value can be calculated using the provided data in Table 2.
Step 8
Plot a graph of Ecell against ln([Zn2+]/[Cu2+]) on the grid.
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To plot the graph, identify the E<sub>cell</sub> values from Table 2 and the corresponding natural logarithm of the concentration ratios. Mark the points accurately on the grid as per the given values.
Step 9
Calculate the gradient of your plotted line on the graph in question 03.6.
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The gradient, based on the plotted values, can be calculated to be approximately -0.013 V, indicating the relationship between the concentrations and the cell potential.
Step 10
Use your gradient to calculate the temperature, T, at which the measurements of Ecell were taken.
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To find the temperature, use the equation:
Ecell=−(4.3×10−5imesT)+Ecell
Solving for T using the given values gives T = 302 °C = 575 K.
Step 11
Use data from Table 2 in question 03.6 to calculate the electrode potential for the Zn2+/Zn electrode in experiment 2.
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The electrode potential for the Zn<sup>2+</sup>/Zn electrode can be calculated using the Nernst equation based on the data from experiment 2 in Table 2.
Step 12
Give one reason why your calculated value is different from the standard electrode potential for Zn2+/Zn electrode.
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The calculated value may differ from the standard electrode potential due to concentration variations and non-ideal behavior of the solutions under the experimental conditions.
