Redox and Electrode Potentials | OCR A-Level Chemistry A (H432)

Redox and Electrode Potentials

78 questions
6 subtopics
Module 5: Physical chemistry and transition elements
Component 01 and Component 03

Redox written as half-equations, redox titrations, standard electrode potentials and the cells built from them, and where feasibility predictions from E values break down..

It covers oxidising and reducing agents, and balancing half-equations, combining half-equations and using oxidation numbers, redox titrations and their calculations, standard electrode potentials and setting up half-cells, the electrochemical series and predicting feasibility and storage cells and fuel cells.

Sample questions from Redox and Electrode Potentials

Answer each one closed book first, then open the answer.

Oxidising and reducing agents, and balancing half-equations

Why does a reducing agent become oxidised during a reaction?

Show the answer
Because it loses electrons to another species, and losing electrons is the definition of oxidation.
Oxidising and reducing agents, and balancing half-equations

In balancing a half-equation, how do you balance atoms other than oxygen and hydrogen?

Show the answer
Add coefficients to ensure the number of each type of atom (excluding O and H) is equal on both sides.
Combining half-equations and using oxidation numbers

How can you identify which species is oxidised in a redox reaction using oxidation numbers?

Show the answer
The species whose oxidation number increases is the one that has been oxidised.
Combining half-equations and using oxidation numbers

In an electron transfer reaction, how do you identify the species that is oxidised?

Show the answer
It is the species that loses electrons.
Redox titrations and their calculations

In a redox titration calculation, once the moles of the known species are determined, what is the next step?

Show the answer
Use the mole ratio from the balanced equation to find the moles of the unknown species.
Redox titrations and their calculations

How is an iodine–thiosulfate titration used to find the amount of an oxidising agent?

Show the answer
The oxidising agent is added to excess potassium iodide, which it oxidises to iodine, and the iodine released is titrated with sodium thiosulfate solution of known concentration from the burette.
Standard electrode potentials and setting up half-cells

Which half-cell is used as the reference, and what value is it assigned?

Show the answer
The standard hydrogen electrode is the reference half-cell, and it is assigned a standard electrode potential of exactly 0.00 V.
Standard electrode potentials and setting up half-cells

What is the purpose of the salt bridge in an electrochemical cell?

Show the answer
It completes the electrical circuit by allowing ions to flow between the two half-cells to balance the charge, while keeping the two solutions from mixing. It usually contains an unreactive electrolyte such as saturated potassium nitrate.

The 6 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Oxidising and reducing agents, and balancing half-equations	Recall questions on what each agent does, and on balancing a half-equation for atoms, oxygen, hydrogen and charge.	9
Combining half-equations and using oxidation numbers	Recall questions on multiplying and combining half-equations, and on identifying what is oxidised and reduced from oxidation numbers.	9
Redox titrations and their calculations	Recall questions on detecting the end point, why manganate(VII) is self-indicating, and using the mole ratio from the balanced equation.	25
Standard electrode potentials and setting up half-cells	Recall questions on the definition and standard conditions, why the hydrogen electrode is the reference, the salt bridge, and setting up metal, gas and ion half-cells.	12
The electrochemical series and predicting feasibility	Recall questions on what a more positive or more negative E means, calculating cell potential, and why a feasible prediction may not be observed.	8
Storage cells and fuel cells	Recall questions on discharge and charging, the lithium fire hazard, what a fuel cell is, and how its operation differs from a storage cell.	15

Redox and Electrode Potentials is 78 of the 1,913 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.