Oxidation and Reduction

Question 1

What is oxidation?

Answer 1

The addition of oxygen, the loss of electrons and the increase in oxidation number

Question 2

What is reduction?

Answer 2

A loss of oxygen, gain of electrons and decrease in oxidation number

Question 3

What does an oxidising agent do?

Answer 3

causes oxidation and is itself reduced

Question 4

What does a reducing agent do?

Answer 4

causes reduction and is itself oxidised

Question 5

What is the most abundant element on the earths crust and in the human body?

Answer 5

Oxygen

Question 6

What does oxygen combine with?

Answer 6

the vast majority of other elements

Question 7

What is oxygen involved in?

Answer 7

some of the most important chemical reactions - burning, respiration, rusting

Question 8

What did oxidation used to be defined as and give an example?

Answer 8

the addition of oxygen to a substance e.g. C + O2 -> CO2

Question 9

What did reduction used to be defined as?

Answer 9

the removal of oxygen

Question 10

Before the discovery of electrons, what were reactions that involved the addition of oxygen to a substance described as?

Answer 10

oxidation reactions

Question 11

What was removing oxygen from a substance previously described as? Why?

Answer 11

a reduction reaction as the mass to the substance got smaller due to the oxygen being removed

Question 12

What did scientists notice after the discovery of the electron?

Answer 12

Scientists examined reactions more closely and noticed that many chemical reactions involved the transfer of electrons. One substance lost electrons while another gained electrons.

Question 13

What did the transfer of electrons involve?

Answer 13

One substance losing electrons while another gained electrons.

Question 14

What is oxidation?

Answer 14

When an element loses electrons

Question 15

What is reduction?

Answer 15

Reduction is when an element gains electrons

Question 16

What do we use to remember oxidation and reduction?

Answer 16

OIL RIG

Question 17

What does OIL RIG stand for?

Answer 17

Oxidation Is Loss, Reduction Is Gain

Question 18

Write down a formula to show oxidation and reduction explaining what has been oxidised and why

Answer 18

Zn + Cu2+ -> Zn2+ + Cu (remember Zn is more positive so it lost negatives so it has been OXIDISED not REDUCED)

Question 19

When do oxidation and reduction occur?

Answer 19

At the same time

Question 20

If one element loses electrons, what happens to another element?

Answer 20

It gains electrons

Question 21

Give two examples of REDOX reactions

Answer 21

1. MgO -> Mg2+ + O2-

2. Zn + Cu2+ -> Zn2+ + Cu

Question 22

Give an example of a REDOX reaction and explain

Answer 22

MgO -> Mg2+ + O2-
In the above example we can see that the Mg atom loses 2e to become the Mg2+ ion. The O atom gains 2e to become the O2- ion.

Question 23

Name the metals more reactive than hydrogen from most reactive to least reactive

Answer 23

Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe), Tin (Sn), Lead (Pb) and then |Hydrogen| |H|

Question 24

Name the metals less reactive than hydrogen from most reactive to least reactive

Answer 24

Copper (Cu), Mercury (Hg), Silver (Ag), Gold (Au)

Question 25

What is electrolysis?

Answer 25

The use of electricity to bring about a chemical reaction in an electrolyte

Question 26

What is an electrolyte?

Answer 26

An electrolyte is a compound which when molten or dissolved in water will conduct an electric current

Question 27

What is the conduction of electricity due to?

Answer 27

the presence of ions

Question 28

What is the electrochemical series?

Answer 28

a list of elements in order of their standard electrode potential (reactivity - how easily they lose electrons)

Question 29

What are electrodes?

Answer 29

The two rods that dip into the electrolyte and make electrical contact with it

Question 30

What are the two types of electrodes?

Answer 30

Inert (do not react with electrolyte) and Active (react with electrode)

Question 31

What are examples of inert and active?

Answer 31

inert -> graphite and platinum | active -> copper and iron

Question 32

how is the electrochemical series organised?

Answer 32

top of the list readily lose electrons | bottom = unreactive

Question 33

are the electrodes positive or negative?

Answer 33

One electrode is positive and the other is negative

Question 34

is a cathode negative or positive?

Answer 34

negative

Question 35

is an anode positive or negative?

Answer 35

positive

Question 36

how do we remember the charge of cathodes and anodes?

Answer 36

CNAP

Question 37

What does CNAP stand for?

Answer 37

Cathode, Negative, Anode, Postive

Question 38

What happens to electrons in the electrodes?

Answer 38

The battery "pumps" electrons to the negative electrode where they are gained by some species and carried to the positive electrode where they are lost

Question 39

oxidation at anode or cathode?

Answer 39

anode

Question 40

reduction at anode or cathode?

Answer 40

cathode

Question 41

What happens in electrodes connected to a DC current?

Answer 41

Positive ions move to negative electrode and gain electrons | Negative ions move to positive electrode and lose electrons

Question 42

anion positive or negative?

Answer 42

negative

Question 43

cation positive or negative?

Answer 43

positive

Question 44

Write the equations for when an electrical current passes through a solution of potassium iodide using inert electrodes.

Answer 44

Anode (+): 2I- -> I2 + 2e- (loss of electrons - oxidation) Cathode (-): 2H2O + 2e- -> H2 + 2OH- (gain of electrons - reduction)

Question 45

Do K+ ions gain electrons at cathode?

Answer 45

no

Question 46

does K+ + e- -> K takes a lot of energy?

Answer 46

yes

Question 47

is K+ a spectator ion?

Answer 47

yes