3.1.7 Oxidation, Reduction And Redox Equations

Question 1

What is an oxidation state?

Answer 1

Oxidation states tell you the number of electrons that an element has accepted or donated. It is the charge that would exist on an individual atom if the bonding were completely ionic. It can also be applied to covalent compounds.

Question 2

What is oxidation state used for?

Answer 2

To determine if oxidation or reduction has occurred
To work out what has been oxidised and what has been reduced
To construct half equations and balance redox equations

Question 3

What is the oxidation state of uncombined elements?

Answer 3

Zero
-uncombined elements or elements that are bonded to other elements of the same type have an oxidation state of 0.

Question 4

What is the oxidation state of elements bonded to other atoms of the same element?

Answer 4

Zero
-uncombined elements or elements that are bonded to other elements of the same type have an oxidation state of 0.

Question 5

What is the oxidation states of the elements in a compound?

Answer 5

The sum of the oxidation states of the elements in a compound is equal to 0.

Question 6

What is the oxidation state of a complex ion?

Answer 6

The sum of the oxidation states of the elements in a complex ion is equal to the charge on the ion.

Question 7

What is the oxidation state of group 1 metals?

Answer 7

+1

Question 8

What is the oxidation state of group 2 metals?

Answer 8

+2

Question 9

What is the oxidation state of aluminium?

Answer 9

+3

Question 10

What is the oxidation state of fluorine?

Answer 10

-1

Question 11

What is the oxidation state of hydrogen?

Answer 11

+1 (except in hydrides it is -1)

Question 12

What is the oxidation state of oxygen?

Answer 12

-2 (except in peroxides it is -1)

Question 13

What are the rules for writing half equations?

Answer 13

1) balance the species with the variable oxidation state
2) balance oxygen by adding water (if needed)
3) balance hydrogen by adding H+ions (if needed)
4) balance charges by adding electrons

Question 14

What is the oxidation state of a monoatomic ion?

Answer 14

The oxidation state of a monoatomic ion is the same as the charge of the ion.

Question 15

How can you determine if oxidation or reduction has occurred from the oxidation states in an equation?

Answer 15

If the oxidation state of the species increases, then oxidation has occurred
If the oxidation state of the species decreases, then reduction has occurred

Question 16

What is a redox reaction?

Answer 16

The word redox is a combination of oxidation and reduction, and one cannot take place without the other in a reaction. A redox reaction is therefore one in which oxidation and reduction both take place.

Question 17

What is oxidation?

Answer 17

Oxidation is a reaction in which an atom or group of atoms loses electrons.

Question 18

What is reduction?

Answer 18

Reduction is a reaction in which an atom or group of atoms gains electrons.

Question 19

What is an oxidising agent?

Answer 19

An oxidising agent is a species which accepts electrons (so oxidises other species).

Question 20

What is a reducing agent?

Answer 20

A reducing agent is a species which donates electrons (so reduces other species).

Question 21

What are the rules for combining ha;f equations to form a redox equation?

Answer 21

1) one of the half equations must show oxidation and one must show reduction (electrons are added to the right hand side it is oxidation, and to the left if it is reduction)
2)the number of electrons in both half equations must be equal (lowest common denominator)
3) group all of the reactants to one side of the equation and all of the products to the other
4) remove any spectator ions or electrons (common to both sides and are not oxidised or reduced)