Physical 7: Redox

Question 1

What is oxidation?

Answer 1

Loss of electrons
Loss of hydrogen
Gain of oxygen

Question 2

What is reduction?

Answer 2

Gain of electrons
Gain of hydrogen
Loss of oxygen

Question 3

Give two half equations to show how copper is oxidised using oxygen, and then combine them.

Answer 3

1. Oxidation of copper
   Cu(s) –> Cu2+(s) + 2e-
2. Reduction of oxygen
   1/2 O2(g) + 2e- –> O2-(g)
3. Combine
   Cu (s) + 1/2O2(g) –> CuO(s)

Question 4

What is a reducing agent?

Answer 4

An electron donor
Causes other compounds to be reduced
Oxidises itself

Question 5

What is an oxidising agent?

Answer 5

An electron acceptor
Causes other compounds to be oxidised
Reduces itself

Question 6

What is an oxidation state?

Answer 6

A number that describes how many electrons an element or compound has lost or gained

Question 7

What is the oxidation state in any uncombined element?

Answer 7

Zero

Question 8

What is the oxidation state of hydrogen in a compound?

Answer 8

+1
Except for in hydrides, where it will be -1 (e.g. NaH)

Question 9

What is the oxidation state of group 1 elements in a compound?

Answer 9

+1

Question 10

What is the oxidation state of group 2 elements in a compound?

Answer 10

+2

Question 11

What is the oxidation state of group 3 elements in a compound?

Answer 11

+3

Question 12

What is the oxidation state of oxygen in a compound?

Answer 12

-2
Except for in peroxides where it is -1

Question 13

What is the oxidation state of fluorine in a compound?

Answer 13

-1

Question 14

What is the oxidation state of chlorine in a compound?

Answer 14

-1
Except for in compounds that contain fluorine or oxygen

Question 15

What is the sum of all oxidation states in a compound?

Answer 15

Zero
Because all compounds are electrically neutral

Question 16

How do you balance redox equations?

Answer 16

1) Work out the two half equations, one should be reduction and the other oxidation
2) Balance them to have the same number of electrons
3) Combine so that the electrons cancel out on both sides
4) If the same compound is present on both sides, balance them, subtracting from both sides as needed