7. Oxidation, Reduction & Redox

Question 1

What is oxidation?

Answer 1

Loss of electrons, gain of oxygen

Question 2

What is reduction?

Answer 2

Gain of electrons, loss of oxygen

Question 3

What is a redox reaction?

Answer 3

In any reaction where an element is oxidised, and another must be reduced

Question 4

What happens if an element itself is oxidised?

Answer 4

It must reduce the other element (by donating electrons)

Question 5

What is the element that is oxidised known as?

Answer 5

The reducing agent (reductant)

Question 6

Why is the element that is oxidised known as the reducing agent?

Answer 6

It must reduce the element by donating electrons

Question 7

What happens if an element itself is reduced?

Answer 7

It must oxidise the other element (by accepting electrons)

Question 8

What is the element that is reduced known as?

Answer 8

The oxidising agent (oxidant)

Question 9

Why is the element that is reduced known as the oxidising agent?

Answer 9

It must oxidise the element by accepting electrons

Question 10

What is used when it is unclear which element has been oxidised and which reduced?

Answer 10

Oxidation number/state of an element

Question 11

Are S block metals oxidising or reducing agents?

Answer 11

Reducing - they lose electrons in reactions and so are oxidised

Question 12

Do s block metals have positive or negative oxidation numbers?

Answer 12

Positive

Question 13

Which elements will need to have their oxidation numbers worked out?

Answer 13

P and d block elements

Question 14

Why do p and d block elements have to have their oxidation numbers worked out?

Answer 14

They can exhibit more than one oxidation state when they form compounds

Question 15

Are halogens oxidising or reducing agents?

Answer 15

Oxidising - they gain electrons and so are reduced

Question 16

Which element in a compound is taken as the one with a negative oxidation state?

Answer 16

The most electronegative element

Question 17

Why is the most electronegative element the one with a negative oxidation state?

Answer 17

It has more power to withdraw electron density

Question 18

Oxidation state of an uncombined element?

Answer 18

Zero

Question 19

Oxidation state of a simple ion? Are there any exceptions to this?

Answer 19

Charge on ion - exception in some cases (e.g. halogens, hydrogen, oxygen)

Question 20

Oxidation state of group 1 elements in a compound? Are there any exceptions to this?

Answer 20

+1 - no exceptions

Question 21

Oxidation state of group 2 elements in a compound? Are there any exceptions to this?

Answer 21

+2 - no exceptions

Question 22

Oxidation state of fluorine? Are there any exceptions to this?

Answer 22

-1 - no exceptions

Question 23

Oxidation state of oxygen? Are there any exceptions to this?

Answer 23

-2 - except when in peroxides and combined with F

Question 24

Oxidation state of hydrogen? Are there any exceptions to this?

Answer 24

+1 - except in metal hydrides

Question 25

Oxidation state of chlorine? Are there any exceptions to this?

Answer 25

-1 - except when with O or F

Question 26

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

Answer 26

Zero

Question 27

What is the sum of the oxidation states of elements in a polyatomic ion equal to?

Answer 27

The charge on the ion

Question 28

Why is oxygen's oxidation number not -2 when combined with F?

Answer 28

F is more electronegative

Question 29

What is the oxidation number of S in H₂SO₄?

Answer 29

+6

Question 30

What can oxidation states be used to determine?

Answer 30

What has been oxidised and reduced in a reaction (therefore oxidising and reducing agents)

Question 31

What does it mean if the oxidation state of an element increases?

Answer 31

It has been oxidised

Question 32

What does it mean if the oxidation state of an element decreases?

Answer 32

It has been reduced

Question 33

When is a reaction not redox?

Answer 33

When there is no change in oxidation state in a reaction

Question 34

What is a disproportionation reaction?

Answer 34

A redox reaction in which the same substance is both oxidised and reduced

Question 35

Which substances can be split into ions for half equations?

Answer 35

Ionic substances only

Question 36

What happens to polyatomic ions in half equations?

Answer 36

They are not split up into individual element

Question 37

What balances oxygen in half equations?

Answer 37

Water

Question 38

What balances excess hydrogen from water in half equations?

Answer 38

H+ ions

Question 39

In overall redox equations, what needs to be cancelled out?

Answer 39

Electrons

Question 40

How are overall redox equations formed?

Answer 40

By adding the two half equations together - after ensuring the number of electrons are equal (and therefore cancel)