Unit 13 Flashcards Preview

Chemistry > Unit 13 > Flashcards

Flashcards in Unit 13 Deck (49):
1

Metal ores
Sodium =

Rock salt

2

Metal ores
Aluminium =

Bauxite

3

Metal ores

Iron = hematite

4

Method of extraction

Potassium, k. Most reactive
Sodium, na Ores more difficult to
Calcium, ca Decompose
Magnesium, mg More expensive
Aluminium , al More difficult
---------------------------------------------
Carbon
---------------------------------------------
Zinc, zn Heating with a reducing agent
Iron, fe (Carbon or carbon monoxide)
Lead, pb
---------------------------------------------
Hydrogen
---------------------------------------------
Copper, cu Occur naturally as elements
Silver, ag So no chemical reaction is needed
Gold, au Only separation from impurities

5

Extraction of zinc from zinc blend

Zinc is mainly zinc sulphide, ZnS. First it is roasted in air, giving zinc oxide

Zinc sulphide + oxygen --> zinc oxide + sulphur dioxide
2ZnS + 3O --> 2ZnO + 2SO2
Then the oxide is reduced in one of the two ways below:
1. Using carbon monoxide. This is carried in a furnace:
Zinc oxide + carbon monoxide --> zinc + carbon dioxide
ZnO + CO --> Zn + CO2
The final mixture contains zinc and a slag of impurities. The zinc is separated from it by fractional distillation

2. Electrolysis

6

Extraction of iron

A mixture called the charge, containing the iron ore, is added through the top of the furnace. Hot air is blasted in through the bottom. After a series of reactions, liquid iron collects at the bottom of the furnace

The charge contains three things
1. Iron ore.
2. Limestone
3. Coke

7

The reactions in a blast furnace
Stage 1: the coke burns giving off heat

The blast of hot air starts the coke burning. It reacts with the oxygen in the air, giving carbon dioxide:

Carbon + oxygen--> carbon dioxide
C + 02 = CO2

It's a combustion reaction which means it's a redox reaction. The carbon is oxidised to carbon dioxide. The blast of air provides the oxygen for the reaction.

The reaction is exothermic - it gives off heat , which helps to heat the furnace

8

The reactions In the blast furnace
Stage 2: carbon monoxide is made

The carbon dioxide reacts with more coke, giving carbon monoxide:

Carbon + carbon monoxide --> carbon monoxide
C + CO2 = 2CO

In this redox reaction, the carbon loses oxygen. It is reduced
The reaction is endothermic- it takes in heat from the furnace. This is good because stage 3 needs a lower temperature

9

The reaction in the blast furnace
Stage 3: the iron (111) oxide is reduced

This is where the actual extraction occurs. Carbon monoxide reacts with the iron ore giving liquid iron
Iron + carbon monoxide --> iron + carbon dioxide
Fe2O3 + 3CO --> 2Fe + 3CO2
The iron trickles to the bottom of the furnace
In this redox reaction, carbon monoxide acts as the reducing agent. It reduces the iron (111) oxide to the metal
At the same time the carbon monoxide is oxidised to carbon dioxide

10

What is limestone used for?

The limestone reacts with the sand (silica) in the ore, to form calcium silicate or slag

Limestone + silica --> calcium silicate + carbon dioxide
CaCO3 + SiO2,--> CaSiO3 + CO2

The slag runs down the furnace and floats on the iron
The purpose of this reaction is to remove impurities from the molten iron
Silica is an acidic oxide . It's reaction with limestone is neutralisation (because limestone is a base) giving calcium silicate , a salt

11

Waste gases

Carbon dioxide and nitrogen. They come out the top of the furnace

The carbon dioxide is from the reduction in stage 3. The nitrogen is from the air blast. It has taken part in the reactions so has not been changed

The molten iron is tapped from the bottom. It is impure with carbon as the main impurity . Some is run into moulds to give cast iron this is hard but brittle. But most of the iron is turned into steel

12

Use of aluminium and what properties make it useful

Overhead electricity cables (w steel core for strenghth) , coating DVDs and cds, cooking foil and food cartons , drink cans

Good conductor of electricity, ductile , resists erosion, non toxic, shiny service that reflects the laser beams that reads cds and dvds, can be rolled into thin sheets

13

Uses for copper and what properties make it useful

Electrical wiring , roofing , saucepan bases

One of the best conductors of electricity, ductile , malleable , develops an attractive protective coating conducts heat well , unreactive , tough

14

Uses for lead and what properties make it useful

Holding the glass in stained glass windows, and sealing joins in roofs car batteries

Easy to bend at room temp , unreactive
Gives a current when connected to lead oxide in an electrolyte (dilute sulphuric acid)

15

Uses of zinc and what properties make it useful

Protecting steel from rusting coating or galvanising iron and steel for torch batteries

Offers sacrificial protection if coating cracks gives a current when connected to a carbon electrode, in an electrolyte

16

Uses of silver and what properties make it useful

Electrical connections inside mobile phones, keyboards, and photovoltaic (PV) cells mirrors , and mirrored sunglasses jewellery

The best metal of all at conducting electricity, ductile.
Reflects light very well, even in a very thin coat looks good, and resists corrosion

17

Uses of titanium and what properties make it useful

Tooth implants, and replacement hip and knee joints. Exhaust pipes for planes pipes and tanks in chemical factories

18

What is an alloy

A mixture of metals that changes there properties or increase them. Turing a metal into an alloy increases its range of uses

19

How to make mild steel

When Carbon (0.5%) is mixed with pure iron the result is mild steel

20

What are the uses of mild steel

Building, ships , car bodies and machinery

21

How to make stainless steel

When nickel and chromium are mixed with iron, the result is stainless steel. This Is hard and rustproof

22

Uses of stainless steel

Car parts, kitchen sinks and cutlery

23

Atoms in a pure metal

They are arranged in a regular lattice. (In fact they are metal ions) in a sea of electrons)

24

When pressure is applied to a metal, for example by hammering the metal

The layers can slide over each other easily. That is why a metal is malleable and ductile

25

Structure when the metal turns to an alloy

New atoms enter the lattice. The layers can no longer slide easily. So the alloy is stronger than the original metal

26

The first stage of making steels

Unwanted impurities are removed from the iron

The molten iron from the blast furnace is poured into an oxygen furnace. Calcium oxide is added, and a jet of oxygen is turned on. The calcium oxide neutralises any acidic impurities, forming a slag that is skimmed off. The oxygen reacts with the other burning them away

27

The second stage of making steels

Then other elements may be added

This is measured out carefully, to give steels with the required properties

28

What is the alloy stainless steel made up of

70% iron
20% chromium
10% nickel

29

Special properties of a stainless steel

Does not rust

30

Uses of stainless steel

Car parts, kitchen sinks, cutlery, tanks and pipes in chemical factories, surgical instruments

31

What is aluminium (alloy number 7075 TF) made from

90.25% aluminium
6% zinc
2.5% magnesium
1.25% copper

32

What are the properties of aluminium (alloy number 7975 TF)

Light but very strong

33

Uses of aluminium (7075 TF)

Aircraft

34

What is brass made from

70% copper
30% zinc

35

What are brass' special properties

Harder than copper, does not corrode

36

What are the uses of brass

Musial instruments, ornaments, door knobs and other fittings

37

What is bronze made of

95% copper
5% tin

38

Special properties of bronze

Harder than brass, does not corrode, chimes when struck

39

Uses of bronze

Statues, ornaments, church bells

40

Why have hundreds of aluminium alloys been made?

Aircrafts need materials that are light but very strong , and resistant to corrosion. Pure aluminium is light , but not strong enough. So hundreds of aluminium alloys have Been developed, for aircraft parts

41

What is corrosion

When a metal is attacked by air, water or other substances in its surrounding is said to make a metal corrode

The more reactive a metal is, the more readily it corrodes

42

What does rusting involve

Rusting needs both air and water.

43

The chemical equation for how iron is oxidised.

4Fe. +. 302 + 2H20. ---> 2Fe2O3H2O
Iron + oxygen + water ---> hydrated iron(111) oxide(or rust)

44

How to prevent rusting

1. Coat the metal with something to keep the air and moisture out.

Paint
Grease
Plastics
Another metal

45

What is galvanizing

By dipping iron into molten zinc

46

What is the process of tin plating

Deposited on the steel by electrolysis

47

How to prevent rusting with chromium

Coating with chromium. The chromium is deposited by electrolysis

48

Using sacrificial protection to prevent rusting

This is when a more reactive metal is attached to the metal and it corrodes instead of the steel.

49

Does aluminium corrode?

No, because a coat of aluminium oxide forms on the aluminium which acts as a seal preventing corrosion