Redox Reactions

Question 1

In terms of electrons, oxidation is:

Accepted Answer

loss of electrons — OIL RIG: Oxidation Is Loss of electrons.

Question 2

In terms of electrons, reduction is:

Accepted Answer

gain of electrons — OIL RIG: Reduction Is Gain of electrons.

Question 3

An oxidising agent is a substance that:

Accepted Answer

gains electrons and is itself reduced — An oxidising agent takes electrons from another substance, so it is itself reduced.

Question 4

A reducing agent is a substance that:

Accepted Answer

donates electrons and is itself oxidised — A reducing agent gives electrons to another substance, so it is itself oxidised.

Question 5

What is the oxidation number of sulfur in the sulfate ion, SO₄²⁻?

Accepted Answer

+6 — Each O is −2 (total −8); overall charge −2, so S = +6 (+6 − 8 = −2).

Question 6

In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, which species is oxidised?

Accepted Answer

Zn — Zn goes from 0 to +2, losing electrons, so zinc is oxidised.

Question 7

Acidified potassium manganate(VII) acts as an oxidising agent. When it is reduced its colour changes from:

Accepted Answer

purple to colourless — Manganate(VII) is purple; when reduced (to Mn²⁺) it becomes colourless.

Question 8

A more reactive metal displacing a less reactive metal from its salt solution is an example of:

Accepted Answer

a redox reaction — Electrons transfer between the metals, so displacement is a redox reaction.

Question 9

During reduction, the oxidation number of an element:

Accepted Answer

decreases — Gaining electrons lowers the oxidation number, so reduction decreases it.

Question 10

When aqueous chlorine is added to potassium iodide solution, iodine is formed. In this reaction chlorine acts as:

Accepted Answer

an oxidising agent — Chlorine removes electrons from iodide ions (oxidising them), so chlorine is the oxidising agent.