1. Redox Reactions

Question 1

Oxidation & Reduction Definition

In Terms of Oxygen

Answer 1

Oxidation is the gain of oxygen by a substance with no other changes to the substance.
Reduction is the loss of oxygen by a substance with no other changes to the subtance.

Question 2

Oxidation & Reduction Definition

In Terms of Hydrogen

Answer 2

Oxidation is the loss of hydrogen by a substance with no other changes to the substance.
Reduction is the gain of hydrogen by a substance with no other changes to the substance.

Question 3

Oxidation & Reduction Definition

In Terms of Electrons

Answer 3

Oxidation is the loss of electrons by a substance.
Reduction is the gain of electrons by a substance.

Question 4

Oxidation & Reduction Definition

In Terms of Oxidation State

Answer 4

Oxidation is the increase in oxidation state of an element in a substance during a reaction.
Reduction is the decrease in oxidation state of an element in a substance during a reaction.

Question 5

Oxidising Agent & Reducing Agent

Definition

Answer 5

An oxidising agent is a substance that oxidises another substance while itself is being reduced.
A reducing agent is a substance that reduces another substance while itself is being oxidised.

Question 6

Electronegativity Values Order

For Common Non-Metals

Answer 6

F > O > Cl > N > Br > I > C > H

Question 7

Disproportionation Reaction

What is it?

Answer 7

A disproportionation reaction is a reaction where a single substance is both oxidised and reduced in the reaction.

Question 8

Chemical Reactions that are Not Redox Reactions

Answer 8

1. Neutralisation
2. Precipitation
3. Reaction of acid and carbonates
4. Thermal decomposition of carbonates

These reactions are not redox reactions because the oxidation state of all the elements in the reactants remain unchanged at the end of the reaction.

Question 9

What is
Acidified Aqueous Potassium Manganate(VII)
used for?

KMnO₄ / H⁺

Answer 9

Acidified aqueous potassium manganate(VII) is an oxidising agent used to test for reducing agents.

In the presence of a reducing agent,
Purple acidified aqueous potassium manganate(VII) turns colourless.
KMnO₄ is reduced because the oxidation state of manganese decreases from +7 in MnO₄^- to +2 in Mn²⁺.

MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4 H₂O

Question 10

What is
Acidified Aqueous Potassium Dichromate(VI)
used for?

K₂Cr₂O₇ / H⁺

Answer 10

Acidified aqueous potassium dichromate(VI) is an oxidising agent used to test for reducing agents.

In the presence of a reducing agent,
Orange acidified aqueous potassium dichromate(VI) turns green.
K₂Cr₂O₇ is reduced because the oxidation state of chromium decreases from +6 in Cr₂O₇^2- to +3 in Cr³⁺.

Cr₂O₇^2- + 14H⁺ + 6e^- → 2Cr³⁺ + 7H₂O

Question 11

What is
Aqueous Iron(III) Chloride
used for?

FeCl₃

Answer 11

Aqueous iron(III) chloride is an oxidising agent used to test for reducing agents.

In the presence of a reducing agent,
Yellow acidified aqueous iron(III) chloride turns pale green.
FeCl₃ is reduced because the oxidation state of iron decreases from +3 in Fe³⁺ to +2 in Fe²⁺.

Fe³⁺ + e^- → Fe²⁺

Question 12

What is
Aqeuous Iodine
used for?

I₂

Answer 12

Aqueous iodine is an oxidising agent used to test for reducing agents.

In the presence of a reducing agent,
Brown aqueous iodine turns colourless.
I₂ is reduced because the oxidation state of iodine decreases from 0 in I₂ to -1 in I^-.

I₂ + 2e^- → 2I^-

Question 13

What is
Aqueous Potassium Iodide
used for?

KI

Answer 13

Aqeous Potassium Iodide is a reducing agent used to test for oxidising agents.

In the presence of an oxidising agent,
Colourless aqueous potassium iodide turns brown.
(Black solid may also be seen if excess iodine is formed as it remains as a insoluble precipitate)
KI is oxidised because the oxidation state of iodine increases from -1 in I^- to 0 in I₂.

2I^- → I₂ + 2e^-

Question 14

What is
Aqueous Iron(II) Sulfate
used for?

FeSO₄

Answer 14

Aqueous iron(II) sulfate is a reducing agent used to test for oxidising agent.

In the presence of an oxidising agent,
Pale green iron(II) sulfate turns yellow.
FeSO₄ is oxidised because the oxidation state of iron increases from +2 in Fe²⁺ to +3 in Fe³⁺.

Fe²⁺ → Fe³⁺ + e^-

Question 15

Other Examples of Oxidising and Reducing Agents

Answer 15

Oxidising Agents

• Non-metals such as Cl₂, Br₂, I₂ (reduced to Cl^-, Br^-, I^-)
• Oxygen
• Ozone
• Nitric acid
• Concentrated sulfuric acid

Reducing Agents

• Metals such as K, Na, Mg (oxidised to K⁺, Na⁺, Mg²⁺)
• Hydrogen gas (oxidised to H₂O when used in reduction of metal oxides)
• Carbon (oxidised to CO₂ when used in reduction of metal oxides)
• Carbon monoxide
• Sulfur dioxide