11. Extracting Metals - Alcester · PDF fileusing materials from the Earth. ... 9 of 27...

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Limestone

Extracting Metals

Crude Oil

Alkanes

Alkenes


Where do building materials come from?

glass is made from sand and limestone

bricks are made from clay

cement is made from limestone or clay.

Buildings are constructed

using materials from the Earth.

Some ‘cut rocks’, including

granite, marble and limestone,

make excellent building

materials.

Changing or combining rocks

from the Earth provides other

useful materials:


What is limestone?

Limestone is an attractive pale yellow or grey stone.

Limestone is used during the

production of other building

materials including:

cement

concrete

It is also used to extract impurities from iron in a blast

furnace, which produces a useable metal from iron ore.

mortar

glass

Blocks of cut limestone are

used as a material for buildings

and statues.


Cement is used as a binder in concrete and mortar.

What is cement?

It is made by heating limestone or clay

and adding gypsum (a compound from

limestone). This mixture is then ground

into a powder.

Mortar is made from cement, water

and sand. It is used in bricklaying and

stonework.

An even layer of mortar is spread

between the bricks or stones to hold

them firmly together.

After the powder is mixed with water,

it will harden to form a strong glue.


What is reinforced concrete?

Although concrete is a very hard material, it is not very

flexible. This means that when it is stretched it can break.

Concrete has a low resistance to tension forces.

Steel rods are used to increase the

strength and flexibility of concrete.

This is called reinforced concrete.

This material can support 300 to

500 times the combined mass of

steel and concrete it is made from.

Reinforced concrete has many

uses, including lamp-posts,

railways and as a structural

material to support buildings.


How is concrete made?

Concrete is made from sand,

cement and water but it is

harder than mortar because

it also contains gravel.

What is the word equation for making concrete?

Concrete is harder than mortar. It is sometimes described

as an artificial rock.

It is used for the foundations

of buildings and for large

structures, such as car parks.

cement sand water concrete + + gravel +


When limestone is heated strongly, a

chemical reaction takes place. Calcium

carbonate breaks down and forms calcium

oxide and carbon dioxide. This type of

reaction is called thermal decomposition.

Limestone is a valuable material because it can be used as

the starting point for many other materials.

calcium carbonate

calcium oxide

carbon dioxide +

What is thermal decomposition?

A lime kiln is often used for this reaction.

The limestone is heated to 900 °C. This

method has been used for centuries.

What is the word equation for this reaction?


magnesium carbonate

magnesium oxide

carbon dioxide +

What about other metal carbonates?

Other metal carbonates can decompose in a similar way to

calcium carbonate, when they are heated.

metal carbonate

metal oxide

carbon dioxide +

What products are formed when copper carbonate

decomposes on heating?

The general equation for the thermal decomposition of a

metal carbonate is:

For example, when magnesium carbonate is heated it

breaks down to form magnesium oxide and carbon dioxide.


The chemical name for slaked lime is calcium hydroxide.

How is slaked lime made?

calcium oxide

water calcium hydroxide +


Uses of slaked lime include glass manufacture

and neutralization of the effects of acid rain.

Quicklime is used as an industrial drying

agent and to make slaked lime.

Calcium oxide, a product of the thermal

decomposition of limestone, is also

called quicklime.

Slaked lime is made by adding water to quicklime.


Why does carbon dioxide turn limewater cloudy?

Fully dissolving calcium hydroxide in water forms limewater.

Limewater is used to test for carbon dioxide.

When carbon dioxide gas is bubbled through

limewater, the limewater becomes cloudy.

The carbon dioxide reacts with calcium hydroxide

to form calcium carbonate and water.

The solid calcium carbonate is held in suspension,

which gives the limewater a cloudy appearance.


calcium carbonate

calcium hydroxide (aq)

carbon dioxide + + water


Summary of uses of limestone products

Slaked lime, calcium hydroxide, is used to

make the building materials mortar and glass.

Slaked lime is alkaline. It can be sprayed on

agricultural fields to reduce soil acidity and

on lakes to neutralize the effects of acid rain.

Quicklime, calcium oxide, is used in making

steel and as an industrial drying agent. It can

be mixed with water to form slaked lime.

Limewater is made by fully dissolving slaked lime

in water. It is often used to test for carbon

dioxide. This is because limewater turns cloudy

in the presence of carbon dioxide.

The products of limestone have many uses.


Limestone and its products can be involved in various useful

chemical reactions:

Summary of limestone chemistry

calcium oxide

water calcium hydroxide +

calcium carbonate

calcium oxide

carbon dioxide +

thermal decomposition of limestone

production of slaked lime

using limewater to test for carbon dioxide.

calcium carbonate

calcium hydroxide (aq)

carbon dioxide + + water


How does quarrying affect the environment?

Limestone is an essential

building material. Millions of

kilograms of limestone are

extracted every year for use in

construction and industry.

However, quarrying limestone

can cause environmental

damage.

Limestone is often found in areas of outstanding natural

beauty. Quarrying can leave scars on the landscape.

Explosives used in quarrying produce noise and dust.

Air and noise pollution is caused by lorries transporting

limestone from the quarry.


Impacts of limestone quarrying


There are two main ways of extracting metals from their ores:

burning ores with carbon (reduction)

electrolysis

How do mining companies decide which method to use?

Gold and other unreactive metals occur

native. Metals that are found in the ground

as uncombined elements do not require

further extraction.

What methods are used to extract metals?

Most metals are found combined with other elements, as

compounds in ores. These metals need to be separated

from the other elements that they are combined with using

chemical reactions.

Extraction methods vary for different metals.


Metals are often found combined with oxygen as oxides.

To obtain the metal, the oxygen must be removed.

In this reaction, the carbon removes oxygen from lead oxide.

This occurs because carbon is more reactive than lead.

What is reduction?

The removal of oxygen from a substance is called reduction.

Carbon can be used to extract metals by reduction.

lead oxide + carbon lead carbon

monoxide +

PbO C Pb CO + +

metal oxide (in ore) metal reduction

The addition of oxygen to a substance is called oxidation.


Reactions of metal oxides and carbon


Extracting iron in industry


Which metals does carbon reduce?

A metal can be reduced by carbon if it

is less reactive than carbon and so

appears below carbon in the reactivity

series.

Using the reactivity series, can you name

a metal that cannot be extracted from its

ore using carbon?

If a metal is more reactive than carbon,

other chemical reactions and processes

must be used in its extraction.

Certain metals, such as iron, can be

only be reduced using carbon if they

are heated to very high temperatures.

potassium sodium calcium

magnesium aluminium

zinc iron

copper

gold

lead

silver

(carbon)

(hydrogen)

platinum


How can the impacts of extraction be reduced?

New mining techniques can decrease the effects of metal

extraction on the environment.

Leaching uses less electricity than traditional

mining and does not produce waste gases.

Copper ores are treated with and dissolved in

dilute sulfuric acid, producing copper sulfate.

Electrolysis is then used to extract the copper.

Certain bacteria can also be used to dissolve

ores and form copper sulfate.

Phytomining uses plants to absorb metals

from the soil. The process can be used to

clean contaminated land. Treating the plants

with certain chemicals increases their ability

to accumulate minerals in their cells.


How can recycling help?

Recycling creates less waste and reduces

the number of sites that have to be mined.

Recycling uses up to 95% less electricity

than producing metals from ores.

Metals are easier to recycle than plastic and they retain

their original properties, such as conductivity and hardness.

Recycling costs less than extracting

metals and can be profitable.

One problem is that metallic materials in recycled objects are

often mixtures of different metals. This can mean that

obtaining pure metals from recycling is more expensive, as

it may use more electricity than extracting metals from ores.


What is crude oil?

Crude oil is a fossil fuel and one of the most important

substances in the world. It is a mixture of hundreds of

different compounds.

Crude oil is used to make

fuels for transport, heating

and generating electricity.

It is also used to make

plastics and hundreds of

different types of chemicals.

Every day, the world uses over 70 million barrels of oil. If you

filled bath tubs with this amount of oil and put them end-to-

end, they would stretch round the Earth 7.5 times!


How was crude oil made?

Crude oil is thought to have been

made from the remains of marine

plants and animals that died

millions of years ago.

These remains sank to the

bottom of the sea, where they

were buried in layers of sand and

mud, preventing them from rotting. These

layers gradually became sedimentary rock.

Over millions of years the layers of rock built up, increasing

the heat and pressure. This caused the remains to be broken

down into the molecules that form crude oil and natural gas.


Hydrocarbons in crude oil

Many compounds in crude oil only contain the elements

carbon and hydrogen. They are called hydrocarbons.

Most hydrocarbons in crude oil are compounds called

alkanes. Alkanes contain a single chain of carbon atoms

with hydrogen atoms bonded along the side.


What are alkanes?

Alkanes are a family of hydrocarbon compounds with the

general formula CnH2n+2.

The simplest alkane is methane.

It has the formula CH4.

The second simplest alkane is

ethane. It has the formula C2H6.

The third simplest alkane is

propane. It has the formula C3H8.


Finding crude oil at sea

Crude oil is often found trapped in rocks of the sea bed.

Oil rigs or drilling

platforms are used to

drill through the sea

bed to obtain the oil.

Once the oil has been

removed from the sea

bed, it is pumped in long

pipelines to an oil tanker

terminal or an oil refinery

on land.


Problems with crude oil

Crude oil is extremely useful but it has several drawbacks:

Burning the products of crude oil as fuel produces gases

and particles that contribute to global warming and air

pollution.

Removing oil from the

ground, as well as oil

spillages and slicks, can be

very damaging to wildlife

and the environment.

The high value of oil means it is sometimes the cause of

military conflict, especially because a large amount of oil

comes from countries that are politically unstable.


Crude oil itself has no uses – it must first be processed or

refined. This is done in an oil refinery.

The first step is to

separate

compounds in the

oil into groups

called fractions.

Each fraction

contains a mix of

compounds with

a similar number

of carbon atoms.

How can crude oil be made useful?


Molecule size and boiling point

The more carbon atoms in a hydrocarbon molecule, the

larger the molecule. How does this affect its boiling point?

Generally, the larger a hydrocarbon,

the higher its boiling point.

This is because the intermolecular forces between large

molecules are stronger than the intermolecular forces

between small molecules.

More energy is needed to break the forces between large

molecules, and so the boiling point is higher.

Molecules in crude oil can contain anything from just

1 carbon atom to well over 50.


What is fractional distillation?

Fractional distillation is a process used to separate a

mixture of liquids that have different boiling points.

Fractional distillation is used to separate

crude oil into fractions with different

boiling points. It can be done industrially

and in the laboratory.

When the mixture is heated, liquids with a low

boiling point evaporate and turn to vapour.

Liquids with a higher boiling point remain

as liquid. The vapour can then be

separated from the liquid.


Fractional distillation of crude oil

Crude oil is separated into fractions by fractional distillation.

1. Oil is heated to about 450 °C and pumped

into the bottom of a tall tower called a

fractionating column, where it vaporizes.

2. The column is very hot at the bottom but

much cooler at the top. As the vaporized oil

rises, it cools and condenses.

3. Heavy fractions (containing large molecules)

have a high boiling point and condense near

the bottom of the column.

4. Lighter fractions (containing small molecules)

have a lower boiling point and condense

further up the column.


How does fractional distillation work?


Order of fractions


Supply and demand

The amount of each type of fraction obtained by fractional

distillation does not usually match the amount of each

fraction that is needed.

Crude oil often contains more

heavier fractions than lighter

fractions. Lighter fractions are

more useful and therefore

more desirable.

The large hydrocarbon molecules

in the heavier fractions can be

broken down into smaller, more

useful, molecules to meet demand

for raw materials for fuels and plastics.


Catalytic cracking

Large hydrocarbon molecules can be broken down into

smaller molecules using a catalyst. This is called catalytic

cracking, and is an example of a thermal decomposition

reaction.

The hydrocarbon molecules are

heated until they turn into

vapour, and then mixed with a

catalyst. The molecules break

apart, forming smaller alkanes

and alkenes.

Alkenes are reactive molecules

that are used to make plastics and

other chemicals.


What are alkenes?

Alkenes are a family of hydrocarbon compounds with the

general formula CnH2n.

Alkenes are very similar to alkanes, but they have one

important difference: they contain at least one double

covalent bond between carbon atoms.

The simplest alkene is ethene.

It has the formula C2H4.

The second simplest alkene is

propene. It has the formula

C3H6.


Cracking decane

Decane from the naphtha fraction can be cracked to form

pentane (for use in petrol), propene and ethene.

decane

(C10H22)

pentane

(C5H12)

propene

(C3H6)

ethene

(C2H4)

+ +


Saturated vs. unsaturated

Alkanes are examples of saturated compounds.

Alkenes are examples of unsaturated compounds.

A saturated compound only contains single

covalent bonds between carbon atoms.

An unsaturated compound contains at least one

double covalent bond between carbon atoms.

A test to distinguish between saturated and unsaturated

compounds is to add red bromine water. In the presence of

unsaturated compounds, the red colour disappears.


How does catalytic cracking work?


Catalytic cracking in the lab

Catalytic cracking can be done in the laboratory by heating

mineral wool soaked in oil with a catalyst, producing a gas.

What might this gas be?

mineral wool

soaked in oil

gaseous product

aluminium

oxide catalyst


The stages of fractional distillation


What you need to do at home

Metals – their properties and what they are used for

Aluminium

Copper

Titanium

Iron and Steel

What an alloy is

What each is used for

What the differences are

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