Figure 1 represents the cell used to measure the standard electrode potential for the Fe2+/Fe 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 Fe2+/Fe electrode.
03.1 Name the piece of apparatus labelled A.
03.2 State th... show full transcript
Worked Solution & Example Answer:Figure 1 represents the cell used to measure the standard electrode potential for the Fe2+/Fe 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.
Step 2
State the purpose of A.
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Answer
The purpose of the salt bridge is to complete the circuit by allowing ions to flow between the two half-cells while maintaining electrical neutrality.
Step 3
Name the substance used as electrode B in Figure 1.
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Answer
Electrode B is typically represented by a platinum electrode.
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 | Dilute HCl (1 mol dm^-3) |
| D | Platinum electrode (inert) |
| E | Hydrogen gas at 1 atm and 298 K |
Step 5
Give the ionic equation for the overall reaction in Figure 1.
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Answer
The ionic equation is:
extFe2++2exte−⇌Fe
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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Answer
The change needed is to connect a voltmeter to measure the potential and possibly to increase the concentration of the Fe2+ ions if they are consumed.
Step 7
Complete Table 2 to show the value missing from experiment 4.
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Answer
For experiment 4, the missing value for [Zn2+] is 0.10 mol dm^-3 and Ecell is 1.04 V.
Step 8
Plot a graph of Ecell against ln([Zn2+]/[Cu2+]) on the grid.
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Ensure you correctly label your axes with Ecell (V) and ln([Zn2+]/[Cu2+]).
Step 9
Calculate the gradient of your plotted line on the graph in question 03.6.
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Answer
The gradient, m, of the line is approximately -0.013 V.
Step 10
Using your gradient to calculate the temperature, T, at which the measurements of Ecell were taken.
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Answer
Using the gradient in the equation,
Ecell=(−4.3×10−5×T)+E°cell,
we can rearrange to find T. Given the gradient, T can be calculated as approximately 302 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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Answer
The electrode potential of the Zn2+/Zn electrode is calculated to be -0.80 V.
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 reason for the difference is likely due to deviations from standard conditions or concentration variances when compared to the standard electrode potential.
