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Define the term standard cell potential - CIE - A-Level Chemistry - Question 3 - 2017 - Paper 1
Question 3
Define the term standard cell potential. The standard cell potential is the potential difference between two half-cells, or two electrodes, in a cell under standard... show full transcript
Worked Solution & Example Answer:Define the term standard cell potential - CIE - A-Level Chemistry - Question 3 - 2017 - Paper 1
Step 1
Define the term standard cell potential.
Answer
The standard cell potential refers to the voltage (or potential difference) between two half-cells or electrodes in an electrochemical cell, measured under standard conditions of 1 atm pressure, a temperature of 298 K, and with each solution at a concentration of 1 mol/dm³.
Step 2
Draw a fully labelled diagram of the experimental set-up you could use to measure the standard electrode potential of the Pb²⁺(aq)/Pb(s) electrode. Include the necessary chemicals.
Answer
To measure the standard electrode potential of the Pb²⁺(aq)/Pb(s) electrode, set up a complete electrochemical cell.
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Components of the diagram:
- Use a Pt electrode for connecting to the Pb²⁺(aq) and a Pb(s) electrode immersed in a Pb(NO₃)₂ solution.
- Include a hydrogen gas input for the standard hydrogen half-cell.
- Draw two beakers: one containing the Pb²⁺(aq) solution and the other containing the hydrogen solution.
- A voltmeter should be connected to show the potential difference.
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Label each part clearly:
- Indicate the direction of current flow and all relevant components.
Step 3
The E* for a Pb²⁺(aq)/Pb(s) electrode is –0.13V. Suggest how the E for this electrode would differ from its E* value if the concentration of Pb²⁺(aq) ions is reduced. Indicate this by placing a tick (✓) in the appropriate box in the table.
Answer
If the concentration of Pb²⁺(aq) ions is reduced, the electrode potential, E, will become more negative compared to its standard potential (E*). This shift occurs because decreasing the concentration of Pb²⁺ ions will cause the equilibrium to shift according to Le Chatelier's principle, towards the left, enhancing the reduction potential of the Pb²⁺/Pb reaction. Therefore, in the table, you should place a tick in the 'more negative' box.
Step 4
Explain your answer.
Answer
This explains that the reduction in concentration of Pb²⁺(aq) ions leads to a decrease in the electrode potential due to the shift in equilibrium position. The equation governing the equilibrium is:
Reducing the concentration of products in this equilibrium prompts a shift to favour the reactants, which inherently results in a more negative cell potential.