Redox

Question 1

What is a redox reaction?

Answer 1

Reaction in which reduction and oxidation happen at the same time.

Question 2

What is oxidation?

Answer 2

Gain of oxygen, loss of hydrogen and loss of electrons.

Question 3

What is reduction?

Answer 3

Loss of oxygen, gain of hydrogen and gain of electrons.

Question 4

What are some examples of oxidation reactions?

Answer 4

Combustion
Rusting
Burning of metals and non-metals to form oxides

Question 5

What is the word and symbol equation for the combustion reaction between methane and oxygen?

Answer 5

Methane + Oxygen > Carbon dioxide + Water + Energy

CH4 + O2 > CO2 + H2O

Question 6

What is the word equation for the rusting reaction between iron, water and oxygen?

Answer 6

Iron + Water + Oxygen > Iron(III) oxide

Question 7

What is the word and symbol equation for the reaction of burning magnesium and oxygen to form a metal oxide?

Answer 7

Magnesium + Oxygen > Magnesium oxide

2Mg + O2 > 2MgO

Question 8

What is the word and symbol equation for the reaction of burning sulfur and oxygen to form a metal oxide?

Answer 8

Sulfur + Oxygen > Sulfur dioxide

S(s) + O2(g) > SO2(g)

OR

Sulfur + Oxygen > Sulfur trioxide

2S(s) + 3O2(g) > 2SO3(g)

Question 9

What are some examples of reduction reactions?

Answer 9

Electrolysis
Blast furnace
Haber process
Reduction of copper(II) oxide to copper using hydrogen

Question 10

What is the word and symbol equation for the reaction of electrolysis using aluminium oxide?

Answer 10

Aluminium oxide > Aluminium + Oxygen

2Al2O3 > 4Al + 3O2

Question 11

What is the word and symbol equation for the reaction in a blast furnace using iron(III) oxide and carbon monoxide?

Answer 11

Iron(III) oxide + Carbon monoxide > Iron + Carbon dioxide

Fe2O3 + 3CO > 2Fe + 3CO2

Question 12

What is the word and symbol equation for the reaction in the Haber process between nitrogen and hydrogen?

Answer 12

Nitrogen + Hydrogen > Ammonia

N2 + 3H2 > 2NH3

Question 13

What is the word and symbol equation for the reaction of the reduction of copper(II) oxide to copper using hydrogen?

Answer 13

Copper oxide + Hydrogen > Copper + Steam

CuO + H2 > Cu + H2O

Question 14

What is the chemical name for rust?

Answer 14

Hydrated iron(III) oxide.

Question 15

What are nails in contact with if they are in a test tube of anhydrous calcium chloride?

Answer 15

Oxygen.

Question 16

What are the observations for the nail in a test tube with anhydrous calcium chloride after 1 week?

Answer 16

No rust.

Question 17

What are nails in contact with if they are in a test tube of distilled water?

Answer 17

Oxygen and water.

Question 18

What are the observations for the nail in a test tube with distilled water after 1 week?

Answer 18

Rust.

Question 19

What are nails in contact with if they are in a test tube of boiled water and a layer of oil?

Answer 19

Water.

Question 20

What are the observations for the nail in a test tube with boiled water and a layer of oil after 1 week?

Answer 20

No rust.

Question 21

What are nails in contact with if they are in a test tube of salt water?

Answer 21

Salt, water and oxygen.

Question 22

What are the observations for the nail in a test tube with salt water after 1 week?

Answer 22

Lost of rust.

Question 23

What are barrier methods?

Answer 23

Ways of preventing rusting by stopping moist air from coming into contact with iron.

Question 24

What are some examples of barrier methods?

Answer 24

Painting
Greasing/oiling
Plastic coating
Stainless steel
Tin plating
Chromium plating
Galvanising

Question 25

What are the benefits of painting as a barrier method?

Answer 25

Relatively cheap. Covers large areas, e.g. bridges and gates. Prevents air or moisture getting at iron.

Question 26

What are the benefits of greasing/oiling as a barrier method?

Answer 26

Suitable for covering moving parts, e.g. car engines, bicycle chains. Prevents air getting at items.

Question 27

What are the benefits of plastic coating as a barrier method?

Answer 27

Prevent air and water from reaching iron, e.g. handle bars on bicycle.

Question 28

What are the benefits of stainless steel as a barrier method?

Answer 28

Much harder than iron as mixed with other substances, changing its properties. No longer rusts. Used car car parts, kitchen sinks and cutlery.

Question 29

What are the benefits of tin plating as a barrier method?

Answer 29

Used to coat iron. Less reactive and non-toxic. Deposited using electrolysis.

Question 30

What are the benefits of chromium plating as a barrier method?

Answer 30

Plated by electrolysis. Shiny metal. Used in car bumpers.

Question 31

What are the benefits of galvanising as a barrier method?

Answer 31

Iron coated with layers of zinc by dipping object into molten zinc. Suitable for storing outside, e.g. dustbins and wheelbarrows. Example of sacrificial protection.

Question 32

What is sacrificial protection?

Answer 32

When metal more reactive than iron is plated onto iron object, it will react first, sacrificing itself and protecting iron from rusting. Reacts with oxygen or water, leaving iron free from rust.

Question 33

How is sacrificial protection used to protect iron hulls of ships or water pipes?

Answer 33

Large blocks of magnesium or zinc attached to iron hull of ship or water pipe. Because magnesium or zinc is more reactive than iron, it corrodes first, leaving iron intact. Blocks have to be replaced as will eventually completely corrode away.