Redox i

Question 1

Oxidation number

Answer 1

Tells us the loss and gain of electrons for atoms

Question 2

Oxidation number of un combined elements or combined to identical elements

Answer 2

= 0

Question 3

Oxidation of monatomic ions

Answer 3

The same as its charge

Question 4

Oxidation number of atoms within molecular ions

Answer 4

The numbers add up to the charge of an ion
So use oxidation number rules of other elements eg oxygen to work it out

Question 5

Oxidation number of neutral compounds (salt, simple covalent molecules ’)

Answer 5

The overall oxidation number is 0 so atoms within it’s oxidation number add to 0

Question 6

Hydrogen oxidation number

Answer 6

Always +1
except metal hydrides where it’s -1
(And H2 where it’s 0)

Question 7

Oxygen oxidation number

Answer 7

Always -2
Except in peroxides where it’s -1
And in O2 where it’s 0

Question 8

What can also show oxidation number of a compound or ions

Answer 8

The Roman numeral

Question 9

Sulfate/nítrate ions oxidation number

Answer 9

The Roman numeral eg sulfate (VI) shows that the oxidation number of the non oxygen element (sulfur) is +6

Question 10

Using oxidation numbers to find chemical formulae

Answer 10

Use The Roman numerals and rules for certain elements
Assume charge is 0nu less said otherwise
Assume nitrate is NO3-, sulfate us SO4 2- etc unless told otherwise

Question 11

Redox reaction

Answer 11

When electrons are transferred where one element is reduced and another is oxidised

Question 12

Oxidation

Answer 12

Loss of electrons

Question 13

Reduction

Answer 13

Gain of electrons

Question 14

Oxidising agent

Answer 14

Makes another element lose electrons by gaining them so is reduced

Question 15

Reducing agent

Answer 15

Loses electrons so another element can gain them and be reduced so is oxidised

Question 16

What happens when metals form compounds?

Answer 16

Usually lose electrons and are oxidised

Question 17

What happens when non metals form compounds?

Answer 17

Usually gain electrons and are reduced

Question 18

Disproportionate reaction

Answer 18

When an element is both reduced and oxidised in a single reaction

Question 19

Half equations

Answer 19

Show the oxidation and reduction (so loss or gain of electrons respectively) of a single element in a reaction

Question 20

Half equation for an oxidation reaction

Answer 20

The electron is on the product side to show how electrons were lost from original element
And the charge as a result on products will INCREASE

Question 21

Half equation for a reduction reaction

Answer 21

The electron is on the reactant side to show how element will gain this and be reduced
And the charge on products will DECREASE

Question 22

What do 2 half equations from the same reaction form when combined?

Answer 22

The full redox reaction
But ensure the number of electrons is balanced

Question 23

How can you balance half equations?

Answer 23

First ensure all other atoms are balanced
Balance number of oxygen with H2O on side that is unbalanced
Then balance the H with H+ atoms
Then ensure overall charge is balanced on either side

Question 24

What to remember about balancing half equations?

Answer 24

The number of H also needs to be balanced so ensure only one side has H+ ions