A-Level Chemistry – Redox Basics

25 flashcards covering definitions, rules, examples, and procedures related to redox chemistry, oxidation states, agents, and typical reactions.

What does the term "redox" stand for?

Simultaneous reduction and oxidation occurring in the same chemical reaction.

In electron terms, what is oxidation?

Loss of electrons (increase in oxidation number).

In electron terms, what is reduction?

Gain of electrons (decrease in oxidation number).

What does the acronym OIL RIG help you remember?

Oxidation Is Loss, Reduction Is Gain (of electrons).

What is an oxidation state (oxidation number)?

A number showing how many electrons an atom has gained or lost compared with the uncombined element.

What is the oxidation state of an uncombined element (e.g., O₂, Na, Fe)?

0

For a simple monoatomic ion, how is the oxidation state determined?

It equals the ionic charge (e.g., Na⁺ = +1, Cl⁻ = –1).

What oxidation state do Group 1 metals have in compounds?

+1

What oxidation state do Group 2 metals have in compounds?

+2

What is the usual oxidation state of hydrogen in compounds and its exception?

+1, except –1 in metal hydrides.

What is the usual oxidation state of oxygen in compounds and its two main exceptions?

–2; –1 in peroxides and +2 when bonded to fluorine.

What oxidation state does fluorine always have in its compounds?

–1

For a neutral molecule, what must the sum of oxidation states equal?

0

For a polyatomic ion, what must the sum of oxidation states equal?

The overall ionic charge.

How can you identify a redox reaction using oxidation states?

If at least one element’s oxidation state increases (oxidation) and another’s decreases (reduction).

In the reaction Mg + Cl₂ → MgCl₂, which species is oxidised and which is reduced?

Mg is oxidised (0 → +2); Cl is reduced (0 → –1).

What is a redox half-equation?

An equation showing only the oxidation or only the reduction part of a redox process, including the electrons transferred.

List the three main steps for combining two redox half-equations.

1) Equalise electrons by multiplying equations, 2) add the equations, 3) cancel electrons and any common species.

Outline the four steps for writing half-equations in acidic solution.

1) Balance all atoms except O and H, 2) balance O with H₂O, 3) balance H with H⁺, 4) balance charge with electrons (e⁻).

What is an oxidising agent and what happens to it during a reaction?

A substance that causes oxidation by gaining electrons; it is itself reduced.

Give two common oxidising agents used in A-level chemistry.

Acidified KMnO₄, H₂O₂ (hydrogen peroxide).

What is a reducing agent and what happens to it during a reaction?

A substance that causes reduction by losing electrons; it is itself oxidised.

Give two common reducing agents used in A-level chemistry.

Zn metal, Fe²⁺ ions.

Define disproportionation and give the classic chlorine-water example.

A reaction where the same element is simultaneously oxidised and reduced; e.g., Cl₂ + H₂O → HCl (Cl = –1) + HClO (Cl = +1).

Name three typical redox processes studied at A-level.

Metal displacement reactions, halogen–halide displacement reactions, and redox processes in electrochemical cells.