(U1) Redox

Question 1

What is redox?

Answer 1

Oxidation and reduction occur simultaneously in the same reaction

Redox reactions involve the transfer of electrons between two species.

Question 2

Define oxidation.

Answer 2

Loss of electrons / Increase in oxidation state

Oxidation can also involve the addition of oxygen or removal of hydrogen.

Question 3

Define reduction.

Answer 3

Gain of electrons / Decrease in oxidation state

Reduction can also involve the addition of hydrogen or removal of oxygen.

Question 4

What is an oxidising agent?

Answer 4

Electron acceptor

The oxidising agent is reduced in the process of oxidation.

Question 5

What is a reducing agent?

Answer 5

Electron donor / provider

The reducing agent is oxidized in the process of reduction.

Question 6

What is disproportionation? (3)

Answer 6

• Oxidation and reduction
• of the same element
• in the same reaction

Disproportionation reactions are a form of Redox reaction

Question 7

When 2 electronegative elements are in the same compound, which one has a positive oxidisation number?

Answer 7

The less electronegative element

E.g. F₂O —> F=-1 | O=+2 (as fluorine is more electronegative)

Question 8

What is the oxidation number of Oxygen generally?

What is it in a peroxide?

Answer 8

• usually -2
• -1 in H₂O₂

Question 9

What is the oxidation number of hydrogen generally?

What is it in a metal hydride?

Answer 9

• usually +1
• -1 in metal hydrides e.g. NaH

Question 10

What oxidation number do compounds add to?

Answer 10

0

Question 11

When does the oxidation number of halides change from -1?

Answer 11

When bonding with more electronegative elements such as Oxygen or Fluorine

Question 12

In NH₃, why does the Nitrogen acquire a ∂^- charge?

Answer 12

• The nitrogen atom uses 3 electrons to form covalent bonds with hydrogen atoms,
• electrons unequally shared with Hydrogen atoms due to a large difference in electronegativity

Question 13

What is the O.N. of any ion?

Answer 13

It’s charge

Question 14

When writing half equations, what can be added to each side?

Answer 14

• electrons
• H⁺ ions
• OH^- ions
• H₂O

Remember, find which reduces and oxidises, then apply the rules:

reduction is:

• gain of electrons
• gain of hydrogen
• decrease in oxidation state

Oxidation is the opposite

Question 15

Which elements are the greatest reducing agents?

Give the trend down the group.

Answer 15

• Metals - namely group 1 metals
• reducing ability decreases down the group

Question 16

Which elements are the greatest oxidising agents?

Give the trend down the group

Answer 16

• Halogens
• oxidising ability decreases down the group