1.7 Oxidation, Reduction And Redox Reactions

Question 1

What is oxidation

Answer 1

• The loss of electrons
OR
• Gain of oxygen (or any electronegative element)
• Loss of Hydrogen (or any electropositive element)

Question 2

What is reduction

Answer 2

• The gain of electrons
OR
• Loss of oxygen (or any electronegative element)
OR
• Gain of hydrogen (or any electropositive element)

Question 3

What is an oxidising agent

Answer 3

Species that gains electrons

Question 4

What is a reducing agent

Answer 4

Species that lose electrons

Question 5

What are the half equations and ionic equation for :
SnO + Zn —> ZnO + Sn

Answer 5

Half equations
• Sn2+ + 2e- —> Sn
• Zn —> Zn2+ + 2e-

Ionic equations
• Sn2+ + Zn —> Zn2+ + Sn

Question 6

Define oxidation state

Answer 6

A number which represents the number of electrons lost or gained by an atom of that element in a compound
(If electrons are lost, the number is positive)
(If electrons are gained, the number is negative)

Question 7

What is the Oxidation state of O in OF2

Answer 7

[O] = +2

Question 8

What is the oxidation state of H in KH

Answer 8

[H] = -1

Question 9

What is the oxidation state of Cl in NaClO

Answer 9

[Cl] = +1

Question 10

Define the term disproportionation

Answer 10

Where in a redox reaction, the oxidation states of atoms of the same element, increase for some atoms but decrease for some atoms

Question 11

What is the oxidation state of P in PCl5

Answer 11

[P] = +5

Question 12

What is the oxidation state of N in NH3

Answer 12

[N] = -3

Question 13

What is the oxidation state of As in AsO4^3-

Answer 13

[As] = +5

Question 14

What is the oxidation state of Fe in K4Fe(CN)6

Answer 14

[Fe] = +2

Question 15

Why is 1s2 2s2 2p5 a weaker reducing agent than 1s2 2s2 2p6 3s2 3p6 4s2?

Answer 15

The 2p electron is closer to the nucleus (smaller atom) than the 4s electron. Hence the nuclear attraction is stronger so the 2p electron is lost less easily than the 4s electron

Question 16

What happens in a redox reaction

Answer 16

• Electrons are transferred from one species to another

• One element is oxidised while another is reduced

Question 17

Why is
2CrO4^2- + 2H+ —> Cr2O7^2- + H2O
not a redox reaction

Answer 17

Chromium is oxidised whereas hydrogen remains the same oxidation state (no element is reduced)