Chapter 16: Extraction and Corrosion of metals

Question 1

How are native metals found usually?

Answer 1

Metals that occur uncombined in the ground can usually be found as a metal oxide or a compound that can usually be found as metal oxide or a compound tat can easily be converted to oxide.

Question 2

Importance of carbon

Answer 2

-In order to extract a metal a reducing agent must be used such as carbon.
-Metals below carbon in the series can be extracted by heating their oxides with carbon but that above carbon must be extracted by electrolysis.
-The oxygen in the metal oxides below carbon will form covalent bonds more easily with carbon rather than remain as the oxide ion.

Question 3

What is an ore?

Answer 3

A naturally occurring mineral from which a metal can be extracted.

Question 4

What is the ore of an iron?

Answer 4

The main ore of iron is haematite containing 60% of iron.

Question 5

What is a blast furnace? (6)

Answer 5

-The furnace is a steel tower about 30 meters high.
-It is lined with refractory (heat-resistant) magnesium oxide bricks that are cooled by water.
-The furnace is loaded with a charge of raw materials which consists of iron ore, coke and limestone.
-the charge is sintered the ore is powdered and heated with coke and limestones to make sure the solids mix well and it is mixed with more coke.
-Blasts of hot air are sent into the furnace through holes near the bottom of the furnace.
-A series of chemical reactions take place within the furnace to produce molten iron.

Question 6

What is limestone?

Answer 6

A mineral of calcium carbonate.

Question 7

What is a mineral?

Answer 7

A naturally occurring rock containing particular compound.

Question 8

Reduction of Iron from Haematite (7)

Answer 8

1) The carbon burns in the air blast and the furnace gets very hot from the heat from its exothermic reaction.
2) As CO2 rises through the furnace it reacts with more carbon and is reduced to carbon monoxide.
3) The most important reaction that then occurs is the reduction of the ore by carbon monoxide.
4) The iron produced flows to the bottom of the furnace. Where it can be tapped off as a liquid because the temperature of the furnace at the bottom is higher than the melting point of iron.
5) Silicon (IV) oxide SiO2 is an impurity in iron ore. Limestone is added to remove this impurity. It goes through thermal decomposition in the furnace to produce calcium oxide and CO2.
6) The lime produced then reacts with the silica to form calcium silicate slag.
7) Slag is molten and flows down the furnace forming a layer over the molten iron due to being denser than iron. It is tapped off separately.

Question 9

Whta is slag?

Answer 9

Another mixture of impurities, mainly calcium silicate formed in the blast furnace.

Question 10

What is slag used for?

Answer 10

When solidified it is used for concrete for buildings and road surfacing.

Question 11

Where do the waste gases go? (2)

Answer 11

-The hot waste gases escape from the top of the furnace. The gases are used in that exchangers to transfer heat to the incoming air.
-This helps reduce the energy cost of the process.

Question 12

How pure is iron produced in the blast furnace? (2)

Answer 12

-It is only 95% pure. The impurities are mainly carbon and they also include sulphur, silicon and phosphorus.
-Most of the iron produced in the furnace is taken and purified further and then turned into various forms of steel.

Question 13

What is corrosion?

Answer 13

-The process that takes place when metals and alloys are chemically attacked by oxygen, water or any other substances found in their immediate environment.

Question 14

Why is corrosion bad?

Answer 14

When a metal is attacked by air, water or any other surrounding substances it is said to corrode.
*Calcium will slowly corrode over time into powder.
In the case of iron, this process is called rusting and it is a serious economic problem.

Question 15

What is rusting? (2)

Answer 15

-The corrosion of iron and steel to form rust. (hydrated iron (III) oxide.
-It is a red-brown powder consisting mainly of hydrated iron III oxide.

Question 16

What is essential for iron to rust? (2)

Answer 16

-Water and oxygen are essential for iron to rust.
-the problem is made worse by the presence of salt: seawater increases the rate of corrosion as well as acid rain.

Question 17

What is rusting in aluminium? (4)

Answer 17

-Aluminium is more reactive than iron with air.
-On aluminium a very thin, single, uniform layer of aluminium oxide forms which sticks strongly to the surface of the metal.
-This microlayer seals the metal surface and protects it from further attack.
-Chromium is the same.

Question 18

What happens when iron rusts? (3)

Answer 18

-When iron corrodes, rust forms in flakes.
-It does not form a single layer.
-The attack can continue over tie as the rust flakes come off.

Question 19

What are barrier methods?

Answer 19

Rust can be prevented by coating a material that prevents iron or steel from coming into contact with water and oxygen these are known as barrier methods.

Question 20

Painting (4)

Answer 20

-It is a common method of barrier protection.
-Some paints react with the metal to form a stronger protection.
-However generally painting only protects the metal for as long as the paint is unscratched.
-Regular repainting is often necessary to keep this protection in fact.

Question 21

Oiling and greasing (2)

Answer 21

-The oiling and/ or greasing of the moving parts of machinery forms a protective film, preventing film preventing rusting.
-The treatment must be repeated to continue the protection.

Question 22

Plastic coating (3)

Answer 22

-Plastic coating is used to form a protective layer on items such as refrigerators and garden chairs.
-The plastic poly vinyl chloride.
-PVC is often used for these purposes.

Question 23

Electroplating (4)

Answer 23

-An iron or steel object can be electroplated with a layer of chromium or tin to protect against rusting.
-a tin can is made of steel coated on both sides with a fine layer of tin.
-Tin is used because it is unreactive and non-toxic.
-When both these metals had their layer broken , the iron starts to rust.

Question 24

Galvanising (3)

Answer 24

-The protection of the iron and steel objects by coating them with a layer of zinc.
-This method has a distinct advantage over other methods as it still works even if the zinc layer is badly scratched.
-It is also a form of sacrificial protection if the zinc layer is scratched or broken if the zinc layer is broken it is still corroded away in preference tot he iron as zinc is a more reactive metal than iron.

Question 25

What is sacrificial Protection?

Answer 25

A method of rust protection involving the attachment of blocks of metal more reactive than iron to a structure; this metal is corroded rather than the iron or steel structure.