Electrode Potentials — A-Level Chemistry Revision
Revise Electrode Potentials for A-Level Chemistry. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to Acids & Bases (A-Level)What is Electrode Potentials?
Electrode potentials quantify the tendency of a species to be reduced and gain electrons. Standard electrode potentials (E°) are measured relative to the standard hydrogen electrode (SHE) under standard conditions. These values are used to calculate the electromotive force (e.m.f.) of an electrochemical cell and to predict the feasibility of redox reactions. A more positive E° value indicates a greater tendency for a species to be reduced.
Board notes: All boards cover the calculation of cell e.m.f. and the prediction of redox reaction feasibility. AQA often includes questions on different types of electrochemical cells, including non-rechargeable, rechargeable, and fuel cells. Edexcel may focus on the industrial applications of electrolysis, linking it to electrode potentials. OCR frequently tests the construction of conventional cell diagrams and the role of the salt bridge.
Step-by-step explanationWorked example
Calculate the standard e.m.f. of a cell made from Cu2+/Cu (E° = +0.34V) and Zn2+/Zn (E° = -0.76V) half-cells. Step 1: Identify the positive and negative terminals. The Cu2+/Cu half-cell has the more positive E° value, so it is the positive terminal (where reduction occurs). The Zn2+/Zn half-cell is the negative terminal (where oxidation occurs). Step 2: Apply the formula E°cell = E°(positive) - E°(negative). Step 3: E°cell = (+0.34) - (-0.76) = +1.10V. Since the e.m.f. is positive, the reaction is feasible.
Mini lesson for Electrode Potentials
1. Understand the core idea
Electrode potentials quantify the tendency of a species to be reduced and gain electrons. Standard electrode potentials (E°) are measured relative to the standard hydrogen electrode (SHE) under standard conditions.
Can you explain Electrode Potentials without copying the notes?
2. Turn it into marks
Calculate the standard e.
Underline the method, evidence, or command-word move that would earn credit in A-Level Physical Chemistry 2.
3. Fix the likely mark leak
Watch for this mistake: Getting the formula for cell e.m.f. the wrong way around. The correct formula is E°cell = E°(positive terminal) - E°(negative terminal), which is equivalent to E°(reduced species) - E°(oxidised species). The result must be positive for a feasible reaction.
Write one correction rule before doing another practice question.
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Electrode Potentials practice questions
These are original StudyVector questions for revision practice. They are not official exam-board questions.
Question 1
In one A-Level sentence, explain what Electrode Potentials is testing.
Answer: Electrode potentials quantify the tendency of a species to be reduced and gain electrons. Standard electrode potentials (E°) are measured relative to the standard hydrogen electrode (SHE) under standard conditions.
Mark focus: Precise definition and topic focus.
Question 2
A Electrode Potentials question uses an unfamiliar context. What should the answer do before adding detail?
Answer: It should name the process, variable, equation, particle model, or evidence being tested, then explain the result using precise scientific vocabulary.
Mark focus: Method selection and command-word control.
Question 3
A student makes this mistake: "Getting the formula for cell e.m.f. the wrong way around. The correct formula is E°cell = E°(positive terminal) - E°(negative terminal), which is equivalent to E°(reduced species) - E°(oxidised species). The result must be positive for a feasible reaction." What should their next repair task be?
Answer: Do one Electrode Potentials question and review the mistake type.
Mark focus: Error correction and next-step practice.
Electrode Potentials flashcards
Core idea
What is the main idea in Electrode Potentials?
Electrode potentials quantify the tendency of a species to be reduced and gain electrons. Standard electrode potentials (E°) are measured relative to the standard hydrogen electrode (SHE) under standard conditions.
Common mistake
What mistake should you avoid in Electrode Potentials?
Getting the formula for cell e.
Practice
What is one useful practice task for Electrode Potentials?
Answer one Electrode Potentials question and review the mistake type.
Exam board
How should you use board notes for Electrode Potentials?
All boards cover the calculation of cell e.
Common mistakes
- 1Getting the formula for cell e.m.f. the wrong way around. The correct formula is E°cell = E°(positive terminal) - E°(negative terminal), which is equivalent to E°(reduced species) - E°(oxidised species). The result must be positive for a feasible reaction.
- 2Confusing the direction of electron flow. In an electrochemical cell, electrons always flow from the more negative half-cell to the more positive half-cell, i.e., from the site of oxidation to the site of reduction.
- 3Forgetting that standard conditions are required for E° values to be valid. These conditions are 298K temperature, 1.00 mol dm-3 concentration of ions, and 100 kPa pressure for any gases.
Electrode Potentials exam questions
Exam-style questions for Electrode Potentials with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Electrode Potentials
Core concept
Electrode potentials quantify the tendency of a species to be reduced and gain electrons. Standard electrode potentials (E°) are measured relative to the standard hydrogen electrode (SHE) under standa…
Frequently asked questions
What is the standard hydrogen electrode (SHE)?
The SHE is the reference standard for all other electrode potentials. It consists of hydrogen gas bubbling over a platinum electrode in a solution of H+ ions at 1 mol dm-3 concentration. Its electrode potential is defined as exactly 0.00V under standard conditions.
Can a reaction with a positive E°cell still not happen?
Yes. Standard electrode potentials only predict thermodynamic feasibility. They do not give any information about the rate of reaction. A reaction may have a very high activation energy, making it kinetically stable and proceed immeasurably slowly, even if it is thermodynamically feasible.