Oxidation, Reduction & Redox Equations

Question 1

What is oxidation?

Answer 1

Addition of oxygen
Loss of hydrogen
Loss of electrons

Question 2

What is reduction?

Answer 2

Loss of oxygen
Addition of hydrogen
Gain of electrons

Question 3

What is the oxidation state of an atom?

Answer 3

The charge that would exist on an individual atom if bonds were fully ionic

Question 4

What are oxidation states used for?

Answer 4

Telling if oxidation/reduction has taken place
Work out what has been oxidised and/or reduced
Construct half equations and balance redox equations

Question 5

What are the oxidation states of atoms?

Answer 5

Neutral already, no need to add any electrons

Question 6

What are the oxidation states of cations?

Answer 6

Need 1 electron added to become neutral

Question 7

What are the oxidation states of anions?

Answer 7

Need 1 electron removed to become neutral

Question 8

What is an oxidising agent?

Answer 8

A substance that oxidies another atom or ion by causing it to lose electrons

Question 9

What happens to the oxidising agent itself?

Answer 9

It gets reduced - gaining electrons
Oxidation state decreases

Question 10

What is a reducing agent?

Answer 10

A substance that reduces another atom or ion by causing it to gain electrons

Question 11

What happens to a reducing agent itself?

Answer 11

Gets oxidised - loses/donates electrons
Oxidation state increases

Question 12

What must be present for a reaction to be a redox reaction?

Answer 12

Both an oxidising and reducing agent

Question 13

What are used to show oxidation states of transition metals?

Answer 13

Roman numerals

Question 14

Why are roman numerals used to show the oxidation states of transition metals?

Answer 14

Can have more than one oxidation state so used to distinguish between

Question 15

What are the six rules of oxidation state?

Answer 15

Oxidation state of any uncombined element is zero
Many atoms or ions have fixed oxidation state in compounds
Oxidation state of an element in mono-atomic ion is always same as charge
Sum of oxidation state in compound is zero
Sum of oxidation state in ion is equal to charge
In compound or ion, more electronegative element given oxidation state

Question 16

What is the oxidation state of fluorine?

Answer 16

-1

Question 17

What is the oxidation state of oxygen?

Answer 17

-2

Question 18

What is the oxidation state of hydrogen?

Answer 18

+1

Question 19

When is the oxidation state of hydrogen -1?

Answer 19

In metal hydrides

Question 20

How do you know which element has a positive oxidation state in a molecule?

Answer 20

The more electronegative species will have the negative value

Question 21

How does electronegativity trend across a period?

Answer 21

Increases

Question 22

How does electronegativity trend down a group?

Answer 22

Decreases

Question 23

How can the value of an element’s oxidation state be determined?

Answer 23

Position on periodic table
Other elements present

Question 24

Do metals have positive or negative values in compounds?

Answer 24

Positive

Question 25

Do non-metals have positive or negative values in compounds?

Answer 25

Mostly negative

Question 26

Are oxidation state always whole numbers?

Answer 26

Yes because can't have half electrons Mathematically sometimes work out fractional

Question 27

How is a redox equation balanced?

Answer 27

Write unbalanced equation and indentify atoms which change in oxidation state Deduce oxidation state changes Balance oxidation state changes Balance charges Balance atoms

Question 28

What are redox reactions?

Answer 28

Reactions in which oxidation and reduction take place simultaneously

Question 29

What is a disproportionation reaction?

Answer 29

A reaction in which the same species is both oxidised and reduced

Question 30

How are disproportionation reactions balanced?

Answer 30

Write unbalanced equation and identify atoms that change in oxidation state Deduce oxidation state changes Balance oxidation state changes Balance charges Balance atoms