1. Oxidation and reduction

What are the four ways oxidation and reduction can be defined?

• In terms of the loss and gain of oxygen

• In terms of the gain and loss of hydrogen

• In terms of electron transfer

• In terms of oxidation state

What happens during oxidation in terms of oxygen?

A substance combines with oxygen.

What happens during reduction in terms of oxygen?

Oxygen is removed from a substance.

Give an example of oxidation in terms of oxygen gain

Combustion of metals to form metal oxides

What is the acid-base nature of metal oxides?

Metal oxides are basic in nature

What is an example of oxidation in respiration?

Aerobic respiration uses oxygen to break down glucose and produce energy.

What is the reaction for the reduction of copper(II) oxide by hydrogen?

CuO(s) + H₂(g) → Cu(s) + H₂O(g)

What is disproportionation?

A reaction where a substance is simultaneously reduced and oxidized.

Give an example of a disproportionation reaction.

Decomposition of hydrogen peroxide:
2H₂O₂ → 2H₂O + O₂

How can oxidation and reduction be justified using oxidation states?

A substance is oxidized if its oxidation state increases and reduced if its oxidation state decreases.

What happens in oxidation in terms of hydrogen

Hydrogen is lost.

Give an example of oxidation in terms of hydrogen loss.

4HCl(g) + O₂(g) → 2Cl₂(g) + 2H₂O(g) (Hydrogen is lost from HCl).

What happens in reduction in terms of hydrogen?

Hydrogen is gained.

Give an example of reduction in terms of hydrogen gain.

Hydrogenation of ethene: C₂H₄(g) + H₂(g) → C₂H₆(g).

What is oxidation in terms of electron transfer?

Loss of electrons.

What is reduction in terms of electron transfer?

Gain of electrons.

What happens in the reaction between sodium metal and chlorine gas?

• Sodium is oxidized: 2Na(s) → 2Na⁺ + 2e⁻

• Chlorine is reduced: Cl₂(g) + 2e⁻ → 2Cl⁻

How do photochromic lenses work?

They contain CuCl and AgCl, which react in UV light to darken the lenses and block light transmission.

How is oxidation defined in terms of oxidation states?

If an atom’s oxidation state increases, it is oxidized.

ow is reduction defined in terms of oxidation states?

If an atom’s oxidation state decreases, it is reduced.

What happens in the formation of carbon disulfide (CS₂)?

• Carbon is oxidized from 0 to +4

• Sulfur is reduced from 0 to -2

Given the reaction:
4NaCl + 2H₂SO₄ + MnO₂ → 2Na₂SO₄ + MnCl₂ + 2H₂O + Cl₂
Identify the oxidation states and agents.

• Mn is reduced.

• Cl is oxidized.

• H₂SO₄ is the oxidizing agent.

• NaCl is the reducing agent.

What is the role of oxidation states in redox reactions?

A species is oxidized if its oxidation state increases and reduced if its oxidation state decreases.

What are oxidizing and reducing agents?

• Oxidizing agent: Causes oxidation and gets reduced.

• Reducing agent: Causes reduction and gets oxidized.

Which halogen is the strongest oxidizing agent?

Fluorine (F₂).

Which halogen is the weakest oxidizing agent?

Iodine (I₂).

What is the trend in oxidizing power among halogens?

Decreases down the group (F₂ > Cl₂ > Br₂ > I₂).

Why can't chlorine oxidize fluoride ions?

Because fluorine is a stronger oxidizing agent than chlorine.

What is the trend in metal reactivity?

Metals are more reactive down Group 1.

What is the reaction between Zn and Cu²⁺?

Zn(s) + Cu(NO₃)₂(aq) → Zn(NO₃)₂(aq) + Cu(s)

What is the order of reactivity in metals?

Mg > Zn > Fe > Cu > Ag (Most to least reactive).

What happens when reactive metals react with acids?

They produce hydrogen gas and a metal salt.

Give an example of a redox reaction with acids and metals.

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

What is a half-equation?

An equation showing either oxidation or reduction separately, highlighting electron transfer.

What is the trend in the oxidizing power of halogens?

Fluorine is the strongest oxidizing agent, and iodine is the weakest.

What is the trend in the reducing power of metals?

Group 1 metals are strong reducing agents, and their reducing power increases down the group.

What happens in a metal displacement reaction?

A more reactive metal displaces a less reactive metal from its compound.

Give an example of a redox reaction between acids and metals.

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g).