Unit 3 - Redox Reactions

Question 1

Oxidation

Answer 1

Defined as the loss of electrons

Question 2

Reduction

Answer 2

Defined as the gain electrons

Question 3

How is it clear that a redox reaction thing occured?

Answer 3

If there has been a transfer of electrons, there will be a change in the oxidation number between the reactants and products

OILRIG

Question 4

Conditions of a Redox Reaction

Answer 4

Oxidations and reductions occur simultaneously. The electrons lost by the species undergoing oxidation is gained by the species being reduced

Question 5

Rules 1-3 for assigning oxidation states

Answer 5

1. Metals in group 1 have an oxidation state of +1, none metals in group 17 are -1
2. The oxidation state of an atom in a molecule that only contains only one element is 0
3. For an un-combined atom, the oxidation state is also 0. (Ex. Potassium metal, k, has an oxidation state of 0)

Question 6

Rules 4-6 for assigning oxidation states

Answer 6

4. The oxidation of a monoatomic ion is equal to the charge on the ion (Ex. Calcium Ca2+ has an oxidation state of 2+)
5. Oxygen is -2 except in peroxides (H2O2), when it is -1
6. Hydrogen is +1, except in metal hydrides (LiH), then it is -1

Question 7

Rules 7-8

Answer 7

7. For any neutral compound, the sum of the ocidation state of the atoms must equal 0 (Ex. MgO oxidation state of Mg = +2, and O = -2)
8. For polyatomic ion, the sum of the oxidation states must equal the ionic charge on the ion (Ex. (SO4)-2 has a combined charge of -2, there the oxidation state of O & S must equal -2. If O has an oxidation state of -2 (Rule 5) and there are 4 O’s, the oxidation state of S must be +6 (+6+4(-2) = -2

Question 8

Half Equations #1

Answer 8

When electrons are lost , they appear as product (right-hand side) in the half equation. NO OVERALL LOSS, JUST A TRANSFER

Question 9

Half Equation #2

Answer 9

When electrons are gained, they appear as reactants (on the left-hand side) in the half-equation.

Question 10

Oxidation in metals and non-metals

Answer 10

Metals - low tendency to draw electrons to themselves
Nonmetals - have a high tendency to draw electrons and hence undergo reduction reactions more reguraly

Question 11

Reducing agent

Answer 11

The element that is causing reduction and hence is being oxidised
- loses electrons
- reduces the oxidising agent
- undergoes oxidation

Question 12

Oxidising agent

Answer 12

The element that is causing oxidation and hence is being reduced
- accepts electrons
- oxidises the reducing agent
- undergoes reduction