How are metals extracted from their ores?

How are metals prevented from reverting to their oxides?

Reactivity series

How to extract metals

IRON

Electrolysisbackground

ALUMINIUM

Copper purification END

BRINGS YOU BACK HERE

Preventing iron reverting

Preventing aluminium reverting

Some metals are more reactive than others. A list of metals in order of their reactivity is called the

REACTIVITY SERIES.

Potassium (K)Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Tin (Sn)Lead (Pb)Copper (Cu)Silver (Ag)Gold (Au)Platinum (Pt)

HIGH REACTIVITY

LOWREACTIVITY

An unreactive element, found in the earth’s crust as the metal itself. Little reaction with oxygen.

Reactions with air / oxygen

The metal slowly gets a black covering of copper oxide when

heated.

The metal burns with a bright, white flame, leaving a white ash

– magnesium oxide.

copper + oxygen copper oxide

Cu + O2 CuO

NOT balanced

22

balanced

All these metals burn vigorously with a bright flame.

The burning of magnesium …..

Mg + O2 MgO22

balanced

Potassium (K)Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Lead (Pb)Copper (Cu)Gold (Au)

HIGH REACTIVITY Reactions of metals with water

No reactions.

The hot metal burns with a bright, white flame when steam

is passed over it. It produces magnesium oxide. Hydrogen can be detected..

This state symbol, (g) for “gas” tells us it’s STEAMMg + H2O MgO + H2

magnesium (s) + water (g) + hydrogen(g)magnesium

oxide (s)

balanced

Calcium slowly dissolves in cold water and fizzes.

The solution is an ALKALIThe gas is hydrogen.

calcium(s) + water(l) + hydrogen(g)calciumhydroxide(aq)

liquid water alkalis contain the

hydroxide ion, OH-

Ca + H2O Ca(OH)2 + H22NOT balanced balanced

Sodium and potassium run around on the surface of cold

water, produce heat & dissolve, with lots of fizzing.

The solution is a strong ALKALIThe gas is hydrogen.

sodium (s) + water (l) sodium hydroxide(aq) + hydrogen(g)

Na + H2O NaOH + H2

NOT balanced

2 22

balanced

SUMMARY OF REACTIONS WITH WATER

•The less reactive metals do nothing.

•Magnesium reacts only when heated with steam.

•Calcium reacts gently when cold

•Sodium & potassium react increasingly violently when cold.

IT ALL FITS IN WITH THE REACTIVITY SERIES

Note: metals that react with STEAM produce the OXIDEmetals that react with WATER produce the HYDROXIDE

Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Lead (Pb)Copper (Cu)Gold (Au)

MORE REACTIVE A MORE REACTIVE METAL CAN DISPLACE A LESS REACTIVE ONE FROM ITS COMPOUNDS

Put some zinc metal into blue copper sulphate solution.

Because zinc is more reactive, it has a greater tendency to become a compound than copper has.

In the test tube we see the zinc dissolving, the copper sulphate solution getting less blue and copper metal appearing at the bottom.

The zinc has displaced the copper from its compound.

The zinc displaces the copper and forces the copper to become an element.

Zinc(s) + copper sulphate(aq) zinc sulphate(aq) + copper(s)

copper displaced from its compound

zinc is more reactive & becomes a compound

Zn + CuSO4 ZnSO4 + Cu

NOTE : Lead, for example would not displace iron from iron chloride solution

because lead is LESS reactive.

Pb(s) + FeCl3 (aq) x balanced

REMEMBER The MORE reactive a metal is, the more it likes being in a COMPOUND

The LESS reactive a metal is, the more it likes being an ELEMENT

LESS REACTIVE

Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Lead (Pb)Copper (Cu)Gold (Au)

MORE REACTIVE A MORE REACTIVE METAL CAN DISPLACE A LESS REACTIVE ONE FROM ITS OXIDE

LESS REACTIVE

Heat aluminium powder with powdered iron(III) oxide.

The mixture flares up.The aluminium is displacing the iron from its oxide.The aluminium is taking the oxygen from the iron, leaving iron metal.

Aluminium(s) + iron oxide(s) + iron(s)Aluminium

oxide(s)

Al + Fe2O3 Al2O3 + Fe balancedNOT balanced

2 2

NOTE : There would be no reaction between copper and zinc oxide because copper is LESS reactive.

Cu(s) + ZnO (s) x

Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Zinc (Zn)Iron (Fe)Lead (Pb)Hydrogen (H)Copper (Cu)Gold (Au)

MORE REACTIVE REACTIONS OF METALS WITH ACIDS

LESS REACTIVE

Metals that are more reactive than hydrogen, displace it from the acid and set the hydrogen free as the gaseous element.

Acids are compounds containing hydrogen as the H+ ion.We must include hydrogen in the reactivity series.

React with cold water : violent with acids

Less reactive than hydrogen. Cannot displace it.

These metals have no reaction with acid.

A reaction of moderate speed. Steady production of bubbles.

A more vigorous reaction. Hot solution & lots of bubbles.

Zinc + sulphuric acid zinc sulphate + hydrogen

Metal + acid salt + hydrogen

(s) (aq) (aq) (g)

metal(s) + acid(aq) salt(aq) +hydrogen(g)

ExamplesExamples

lead + nitric acid + hydrogenlead

nitrate

iron + sulphuric acid + hydrogeniron(II)sulphate

magnesiumchloride

hydrochloricacidmagnesium + + hydrogen

Fe + H2SO4 FeSO4 + H2

NOT balanced balanced

balanced

balanced

Mg + HCl MgCl2 + H2 2

Pb + HNO3 Pb(NO3) 2 + H2 NOT balanced

2

EXTRACTING METALS FROM THEIR ORES.

The earth’s crust contains metals and metal compounds, always found mixed with other substances.

Gold is an unreactive metal, at the bottom of the reactivity series. It is found in the earth as the metal itself and chemical separation is not needed.

In ORES, the metal or its compound is concentrated enough to make it economic to extract the metal.

Often an ore contains a metal oxide or something that can easily be changed into a metal oxide.The ore haematite is iron(III) oxide, Fe2O3

The ore bauxite is aluminium oxide, Al2O3

To extract the metal, the oxygen must be removed from the metal oxide.

ThIs process is called REDUCTION.

HOW A METAL IS EXTRACTED FROM ITS ORE DEPENDS ON HOW REACTIVE IT IS.

Aluminium (Al)Zinc (Zn)Iron (Fe)Lead (Pb)Hydrogen (H)Copper (Cu)Silver (Ag)Gold (Au)

MORE REACTIVE

LESS REACTIVE

Hydrogen will displace less reactive metals from oxides of those metals.

Because its more reactive, it is able to remove the oxygen and combine with it to

make water.

So hydrogen can reduce ;

copper oxide silver oxide

Hydrogen cannot reduce ;

lead oxide iron oxide zinc oxide, etc

Pass a stream of hydrogen gas over heated, black copper oxide.

It will gradually go brown as copper metal is made.

copper oxide(s) + hydrogen(g) = copper(s) + water(g)

CuO + H2 Cu + H2O

HOW CARBON CAN BE USED TO EXTRACT A METAL FROM ITS ORE. (this is an important, central point)

Sodium (Na) Calcium (Ca)Magnesium (Mg)Aluminium (Al)Carbon (C)Zinc (Zn)Iron (Fe)Lead (Pb)Copper (Cu)Gold (Au)

MORE REACTIVE

LESS REACTIVE

This is the position of the non-metal, carbon in the reactivity series.

Because it is more reactive, carbon can take the oxygen from the iron oxide.

As a result, iron is obtained from its ore using carbon in the Blast Furnace.

Aluminium has to be extracted from Bauxite using ELECTROLYSIS.

These two methods are considered in the following slides.

A metal such as iron, which is less reactive than carbon CAN be extracted from its ore

using carbon.

Aluminium is MORE reactive than carbon and so carbon does NOT have the ability to remove oxygen from aluminium oxide.

Using first wood and then coal, this has been

known about for thousands of

years. (since the Iron Age)

The difficulty of extracting aluminium from its oxide meant a stronger method, electrolysis, was needed &

this is expensive.Electricity generation is a

modern development.So we have only been able to

extract the more reactive metals in recent times.

or zinc

The raw materials are :• coke (C)• haematite (Fe2O3)• limestone (CaCO3)

EXTRACTION OF IRON IN THE BLAST FURNACE

Hot air is blown in

1. The coke burns in an exothermic reaction. Energy is released, raw material gets hot and carbon dioxide is formed.

2. At the high temperatures, the carbon dioxide reacts with more coke to make carbon monoxide.

carbon + oxygen carbon dioxide

C + O2 CO2

carbondioxide

carbonmonoxide

+ carbon

CO2 + C CONOT balanced

2

balanced

3. The carbon monoxide REDUCES the iron oxide in the ore, into molten iron which flows to the bottom of the furnace.

MOLTENIRON

4. Limestone is added to remove acidic impurities forming a molten slag which floats on top of the iron.

SLAG

wastegases

Hot air

MOLTENIRON

SLAG

The carbon monoxide REDUCES the iron oxide in the ore, into molten iron which flows to the bottom of the furnace.

The process of removing oxygen from the ore is called REDUCTION.

The carbon monoxide combines with the oxygen from the iron ore to produce carbon dioxide.This is called OXIDATION.

Iron(III) oxide + iron + carbonmonoxide

carbondioxide

This is OXIDATION

This is REDUCTIONFe2O3 + CO Fe + CO2

NOT balanced

23 3

balanced

This is the central, important reaction in the Blast Furnace.

HOW CAN IRON BE PREVENTED FROM REVERTING TO ITS OXIDE ?

Iron & steel corrode with air and water more quickly than most transition metals. It can be prevented by :

• connecting iron with a more reactive metal. “Galvanised iron” is the name given to iron plated with zinc. The more reactive metal corrodes first, (zinc) making sure the iron does NOT corrode. That is why the zinc would be called a “sacrificial metal”.

• Steel can be mixed with other metals such as chromium (Cr) to make an alloy which will not rust.Lots of cutlery made in Sheffield is manufactured from this “stainless steel”.

Theory of Electrolysis ALUMINIUM

magnesium

wire

undergroundiron pipe

Here, the more reactive magnesium is being sacrificed, saving the iron pipe.

MAKING ALUMINIUM METAL INDUSTRIALLYUSING ELECTROLYSIS.

The lining of this large tank is made of carbon and is connected to the negative of the voltage supply.

-

This large block of carbon is connected to the positive of

the voltage supply.

+

The raw material from which aluminium is produced is aluminium oxide, Al2O3 which contains the ions Al3+ and O2-

The ore is called BAUXITE which needs purifying to get the aluminium oxide.

The ions must be able to move but melting the aluminium oxide is difficult because of its high melting point.

So the aluminium oxide is dissolved in molten aluminium compound called CRYOLITE at a much lower temperature.

MOLTEN ALUMINIUM OXIDE IN CRYOLITEAl3+

O2-

The ions are attracted as shown

The aluminium forms at the negative electrode

Oxygen forms at the positive electrode

This oxygen reacts with the carbon (+) electrodeand makes carbon dioxide gas.

So the electrode burns away quickly and often has to be replaced.

The oxide ion loses electrons and is oxidised : 2O2- - 4e O2

The aluminium ion gains electrons and is reduced Al3+ + 3e Al

HOW CAN ALUMINIUM BE PREVENTED FROM REVERTING TO ITS OXIDE ?

Aluminium is almost as reactive as magnesium & we might expect it to corrode quickly over time, or to burn up

(oxidise) completely if it got hot. But it does not do this.

Aluminium metalGets covered in a thin

layer of aluminium oxide as soon as it is made.

This surface layer forms a barrier to oxygen and water & so prevents further corrosion.

Aluminium is a useful structural metal, low in density.It can be made harder, stronger & stiffer by mixing it will

small amounts of other metals such as magnesium, to make an alloy.

+-

-----

--

-+

++

++++

PURIFICATION OF COPPER

+

+

- -

The negative electrode is pure copper.

The positive electrode is scrap coppercontaining impurities.

+ is the copper ion, Cu2+

The solution must contain the Cu2+ionCopper sulphate(aq) will do.

The scrap copper dissolves in the

solution.Pure copper gets plated onto the

negative electrode. impuritiesseparated

outOXIDATION AT THE POSITIVE ELECTRODE

2 Cu - e Cu2+

REDUCTION AT THE NEGATIVE ELECTRODE

Cu2+ + e Cu2

These are the remains of some of the earliest Blast Furnaces. (Coalbrookdale Museum of Iron)

To find out more about the Steel Industry, visit :

The Ironbridge Gorge Museums, Telford

Kelham Island Museum, Sheffield

THE END

This is a painting of the “Bedlam” Blast Furnaces at night,

hundreds of years ago.