Topic 3 Redox I

Question 1

Redox reaction

Answer 1

Reaction that involves both reduction and oxidation.

Question 2

Oxidation

Answer 2

Loss of electrons.

Question 3

Reduction

Answer 3

Gain of electrons.

Question 4

Oxidising agent

Answer 4

A species that oxidised another species by removing one or more electrons. When an oxidising reagent reacts, it gains at least 1 electron, so is reduced.

Question 5

Reducing agent

Answer 5

A species that reduces another species by adding at least 1 electron. When a reducing agent reacts, it loses one or more electrons, so is oxidised.

Question 6

Oxidation number

Answer 6

The charge that an ion has, or that it would have, if it were fully ionic.

Question 7

Oxidation number of an uncombined element

Answer 7

0

Question 8

The sum of Oxidation numbers of all the elements in a neutral compound

Answer 8

= 0

Question 9

The sum of Oxidation numbers of all the elements in an ion=

Answer 9

The charge on the ion.

Question 10

The more electronegative element in a substance

Answer 10

Given a negative oxidation number.

Question 11

Oxidation number of fluorine

Answer 11

-1 always.

Question 12

Oxidation number of hydrogen

Answer 12

+1, except when combined with a less electronegative element, then it becomes -1.

Question 13

The oxidation number of oxygen

Answer 13

-2 except in peroxides where it is -1 and when combined with fluorine, when it is +ve.

Question 14

Disproportionation

Answer 14

The simultaneous oxidation and reduction of an element in a single reaction.

Question 15

What happens to Oxidation number of an element when it is reduced?

Answer 15

It decreases.

Question 16

What happens to oxidation number of an element when it is oxidised?

Answer 16

It increases.

Question 17

Disproportionation reaction when NaOH reacts with chlorine:

Answer 17

2NaOH + Cl2 —> NaCl + NaClO + H2O (all aq except water, which is l).

Question 18

SO2

Answer 18

Sulfur(IV) oxide

Question 19

SO3

Answer 19

Sulfur (VI) oxide

Question 20

When are systematic names (Roman numerals in brackets) used?

Answer 20

When an element can have more than 1 Oxidation State.

Question 21

How can we use oxidation numbers to identify the stoichiometric ratio?

Answer 21

Identify the elements whose oxidation numbers have changed. E.g., S changes from +4 to +6, so this is a 2 electron change and Ag changes from +1 to 0– a 1 electron change. This means SO2 to Ag+ is 1:2. Then Balance the electrons, als and Hs.

Question 22

First step when balancing redox equations

Answer 22

Check you have the existing atoms balanced.

Question 23

When balancing equations, what are you allowed to add?

Answer 23

Electrons.
Water.
H+ (or OH- if in alkaline conditions).

Question 24

Typical sequence for balancing equations in acidic or neutral conditions:

Answer 24

Balance the atoms except O and H.
Balance the Os by adding water molecules.
Balances the Hs by adding H+ ions.
Balance the charges by adding electrons.

Question 25

Balancing equations in alkaline conditions

Answer 25

If it’s not obvious where to put the OH- ions, balance it as if it were under acidic conditions, then add the same number of OH- ions to each side to cancel out the H+ ions in each half equation. Where there are OH- ions and H+ ions on the same side, they combine to form water.