CHEMICALS OF THE NATURAL ENVIRONMENT C5 21 ST CENTURY SCIENCE

Extraction of Metals Metals are hugely important to human civilisation and always have been. We use them for a huge variety of purposes both as elements an in compounds. In order to use them they must be extracted and purified.

Metals are hugely important to human civilisation and always have been. We use them for a huge variety of purposes both as elements an in compounds.

In order to use them they must be extracted and purified.

LEARNING OBJECTIVES L7 know that ores are rocks that contain varying amounts of minerals from which metals can be extracted. explain how some metals can be extracted from their metal oxides by heating with carbon. know an example of a metal which can be extracted by heating its oxide with carbon. know that the metal oxide loses oxygen and is reduced while the carbon gains oxygen and is oxidised. By the end of the lesson you should:

know that ores are rocks that contain varying amounts of minerals from which metals can be extracted.

explain how some metals can be extracted from their metal oxides by heating with carbon.

know an example of a metal which can be extracted by heating its oxide with carbon.

know that the metal oxide loses oxygen and is reduced while the carbon gains oxygen and is oxidised.

Getting metals from ores First substances other than the metal compound are removed (concentration). Next the metal itself is extracted from its compound (reduction). Most metals do not occur naturally (native). They have to be extracted from metal containing rocks (ores).

First substances other than the metal compound are removed (concentration).

Next the metal itself is extracted from its compound (reduction).

Extraction of metals and energy changes The more vigorously an element forms compounds the harder it will be to get back that element from its compounds. For example, magnesium gives out lots of heat when it combines with oxygen. This means we will have to put lots of energy back to extract magnesium from magnesium oxide and so it will be hard to extract.

The more vigorously an element forms compounds the harder it will be to get back that element from its compounds.

For example, magnesium gives out lots of heat when it combines with oxygen.

This means we will have to put lots of energy back to extract magnesium from magnesium oxide and so it will be hard to extract.

Extraction processes The Reactivity Series potassium sodium calcium magnesium aluminium zinc iron copper gold (carbon) Increasing reactivity Metals above carbon must be extracted using electrolysis. Metals below carbon can be extracted from the ore by reduction using carbon, coke, or charcoal. Gold and silver often do not need to be extracted. They occur native. The reactivity of a metal determines the method of extraction. lead silver

Extracting methods Here is a list of the symbols of some metals in order of decreasing reactivity- Li, Ce, Mn, Al, Zn, Cd, Sn, Pb, Cu, Pd Use this to assign the most likely method of extraction: native (N), carbon(C), electrolysis (E). Method (N, C or E) Symbol Sn Cd Al Cu Pd Ce Mn Zn Li

Here is a list of the symbols of some metals in order of decreasing reactivity-

Li, Ce, Mn, Al, Zn, Cd, Sn, Pb, Cu, Pd

Use this to assign the most likely method of extraction: native (N), carbon(C), electrolysis (E).

Extracting Gold Because gold occurs native its extraction is a low-tech affair that simply involves finding it!

Because gold occurs native its extraction is a low-tech affair that simply involves finding it!

Iron Iron is a moderately reactive metal. Iron ore is plentiful and relatively easily reduced to iron metal by heating with coal (carbon). It is therefore cheap. It is strong and malleable (non-brittle). Iron is the most commonly used metal.

Iron is a moderately reactive metal.

Iron ore is plentiful and relatively easily reduced to iron metal by heating with coal (carbon). It is therefore cheap.

It is strong and malleable (non-brittle).

Iron is the most commonly used metal.

Reactions - Reduction of iron ore carbon + oxygen  carbon dioxide Carbon dioxide + carbon  carbon monoxide Carbon monoxide + iron oxide  iron + carbon dioxide C(s) + O 2 (g)  CO 2 (g) CO 2 (g) + C(s)  2CO(g) 3CO(g) + Fe 2 O 3 (s)  2Fe(s) + 3CO 2 (g)

Extracting iron – The Blast Furnace

Reactions – Removing impurities Calcium carbonate  calcium oxide + carbon dioxide Calcium oxide + silicon dioxide  calcium silicate CaCO 3 (s)  CaO(s) + CO 2 (g) CaO(s) + SiO 2 (s)  CaSiO 3 (s) This is called SLAG

Extraction of Iron

State Symbols These tell you whether a material is a solid, liquid or gas when you write a symbol equation: Solid: (s) Liquid: (l) Gas: (g) A solution is denoted using the symbol (aq) which is shorthand for “aqueous”.

These tell you whether a material is a solid, liquid or gas when you write a symbol equation:

Solid: (s)

Liquid: (l)

Gas: (g)

A solution is denoted using the symbol (aq) which is shorthand for “aqueous”.

LEARNING OBJECTIVES L8 understand that large amounts of some ores will yield only small percentages of useful minerals, e.g. copper ore. be able to evaluate the impact on the environment of the extraction, use and disposal of metals, from appropriate information. be able to balance equations and to use state symbols in equations. be able to calculate the mass of the metal that can be extracted from a mineral given its formula or an equation. By the end of the lesson you should:

understand that large amounts of some ores will yield only small percentages of useful minerals, e.g. copper ore.

be able to evaluate the impact on the environment of the extraction, use and disposal of metals, from appropriate information.

be able to balance equations and to use state symbols in equations.

be able to calculate the mass of the metal that can be extracted from a mineral given its formula or an equation.

Copper Copper is a metal of low reactivity. It occasionally occurs native but more often occurs as copper compounds. Heating copper compounds with carbon gives copper but this is not pure enough to use for electrical work.

Copper is a metal of low reactivity.

It occasionally occurs native but more often occurs as copper compounds.

Heating copper compounds with carbon gives copper but this is not pure enough to use for electrical work.

LEARNING OBJECTIVES L9 know what happens to the ions when an ionic crystal melts. know that molten ionic compounds and solutions of ionic compounds are electrolytes. be able to explain, in terms of loss and gain of electrons, the formation of the metal at the negative electrode and the non-metal at the positive electrode during electrolysis. be able to use ionic theory to explain the changes that happen to the ions during electrolysis. By the end of the lesson you should:

know what happens to the ions when an ionic crystal melts.

know that molten ionic compounds and solutions of ionic compounds are electrolytes.

be able to explain, in terms of loss and gain of electrons, the formation of the metal at the negative electrode and the non-metal at the positive electrode during electrolysis.

be able to use ionic theory to explain the changes that happen to the ions during electrolysis.

Electrolytic purification The conductivity of copper is drastically reduced by tiny amounts of impurities. Because of this most copper metal is further purified by electrolysis. In this process impure anodes dissolve. This dissolved copper is plated onto a cathode leaving behind impurities.

The conductivity of copper is drastically reduced by tiny amounts of impurities.

Because of this most copper metal is further purified by electrolysis.

In this process impure anodes dissolve.

This dissolved copper is plated onto a cathode leaving behind impurities.

Copper purification: The whole process

Copper ions form at the anode Impure copper is used as the anode of an electrolysis cell. The battery pulls electrons off the copper atoms in the anode. By losing electrons these atoms become copper ions and so the anode slowly ‘dissolves’ away. Impurities just sink to the bottom as ‘anode mud’.

Impure copper is used

as the anode of an electrolysis cell.

The battery pulls electrons off the copper atoms in the anode.

By losing electrons these atoms become copper ions and so the anode slowly ‘dissolves’ away.

Impurities just sink to the bottom as ‘anode mud’.

Copper atoms at the cathode Opposite charges attract. Positive copper ions ( Cu 2+ ) move towards the negative cathode. At the cathode these ions gain electrons and turn into copper atoms. So, during electrolysis a copper cathode gets thicker.

Opposite charges attract.

Positive copper ions ( Cu 2+ ) move towards the negative cathode.

At the cathode these ions gain electrons and turn into copper atoms.

So, during electrolysis a copper cathode gets thicker.

Purification: The half reactions Anode (+ve electrode) Cu(s)  Cu 2+ (aq) + 2e - Cathode (-ve electrode) Cu 2+ (aq) + 2e -  Cu(s)

Copper is purified to improve its NOT CIVIC DUTY Copper is purified by CELERY IS LOST Pure copper forms at the DO TEACH Impurities form called A ODD MENU The anode will slowly DIVE LOSS At the cathode copper ions gain CORN STEEL conductivity electrolysis cathode anode mud dissolve electrons Unscramble the words to end the sentences

Copper is purified to improve its

NOT CIVIC DUTY

Copper is purified by

CELERY IS LOST

Pure copper forms at the

DO TEACH

Impurities form called

A ODD MENU

The anode will slowly

DIVE LOSS

At the cathode copper ions gain

CORN STEEL

Extracting platinum Platinum is a rare and expensive metal used in jewellery and also for plating the fuel nozzles in jet engines. It was first discovered by Europeans in 1735 but in South America the primitive pre-Columbian Indians had been using it for centuries. Approximately where would you place platinum in the activity series? In what form do you think platinum occurs?

Platinum is a rare and expensive metal used in jewellery and also for plating the fuel nozzles in jet engines. It was first discovered by Europeans in 1735 but in South America the primitive pre-Columbian Indians had been using it for centuries.

Purifying copper and electricity Copper is purified using electrolysis. Plan an experiment to investigate factors that might affect the rate of copper production. Include: Any factors that might affect rate. The apparatus you would need. A statement of how you would control variable in an investigation. The number and range of readings. The safety issues you would take into account.

Copper is purified using electrolysis.

Plan an experiment to investigate factors that might affect the rate of copper production.

Include:

Any factors that might affect rate.

The apparatus you would need.

A statement of how you would control variable in an investigation.

The number and range of readings.

The safety issues you would take into account.

Aluminium: properties Aluminium is a reactive metal. We might expect it to corrode easily but a strong coating of oxide on it’s surface prevents this in most everyday situations. It has a low density which leads to its extensive use in the aerospace industry. don't have to copy Al Al Al Al Al Al Al Al Al Al Al Al O O O O O O O O O Coating of oxygen atoms prevents further attack

Aluminium is a reactive metal.

We might expect it to corrode easily but a strong coating of oxide on it’s surface prevents this in most everyday situations.

It has a low density which leads to its extensive use in the aerospace industry.

LEARNING OBJECTIVES L10 be able to describe how aluminium is extracted by electrolysis of aluminium oxide. By the end of the lesson you should:

be able to describe how aluminium is extracted by electrolysis of aluminium oxide.

Aluminium: ores It occurs as bauxite ore which is a form of aluminium oxide. Because aluminium is so reactive carbon is unable to pull away the oxygen from it. It is extracted by electrolysis of molten bauxite. Early attempts at this failed because bauxite is so hard to melt. If cryolite is added, the bauxite melts more easily. This is an essential step in the extraction process. don't have to copy

It occurs as bauxite ore which is a form of aluminium oxide.

Because aluminium is so reactive carbon is unable to pull away the oxygen from it.

It is extracted by electrolysis of molten bauxite. Early attempts at this failed because bauxite is so hard to melt.

If cryolite is added, the bauxite melts more easily. This is an essential step in the extraction process.

A bauxite / cryolite mixture is melted in a steel container containing a carbon lining. Tank lined with carbon cathode Steel case Graphite anodes are inserted into the molten electrolyte ready for electrolysis. Electrolytic extraction don't have to copy Graphite (carbon) anodes Molten electrolyte bauxite + cryolite

Aluminium formation Opposite charges attract. And so positive aluminium ions move towards the negative cathode. At the cathode these ions gain electrons and turn into aluminium atoms.

Opposite charges attract.

And so positive aluminium ions move towards the negative cathode.

At the cathode these ions gain electrons and turn into aluminium atoms.

Oxygen formation Negatively charged oxide ions move to the anode. Here they lose 2 electrons and so turn into neutral oxygen atoms. These atoms rapidly join into pairs to form normal oxygen gas.

Negatively charged oxide ions move to the anode.

Here they lose 2 electrons and so turn into neutral oxygen atoms.

These atoms rapidly join into pairs to form normal oxygen gas.

Carbon dioxide formation Remember the electrolysis is carried out at high temperature. Under these conditions quite a lot of the oxygen reacts with the carbon anode. Carbon dioxide is formed and the anode is rapidly eaten away and frequently has to be replaced.

Remember the electrolysis is carried out at high temperature.

Under these conditions quite a lot of the oxygen reacts with the carbon anode.

Carbon dioxide is formed and the anode is rapidly eaten away and frequently has to be replaced.

Extraction of aluminium: overall siphon Graphite / carbon anodes Molten aluminium Molten electrolyte bauxite + cryolite Tank lined with carbon cathode Molten aluminium out Steel case Vented cover

LEARNING OBJECTIVES L11 Life cycle of metals By the end of the lesson you should:

Life cycle of metals

2 Iron is the most abundant metal in the lithosphere. 3 All the really valuable ores come from underground mining. Metal ores – true or false? 1 All metals are found in the Earth as compounds.

A vein of gold in quartz rock

The mineral ore haematite (iron oxide) is mined as the principal source of the metallic element iron.

A disused tin mine in Cornwall

A crane filling railroad cars in an open cast copper mine

1 The removal of oxygen from a metal compound is called reduction. 2 Carbon is oxidized in a blast furnace. 3 Aluminium oxide conducts electricity when solid and when liquid. Metal extraction – true or false?

A blast furnace runs continuously, making hundreds of thousands of tons of iron per year.

carbon anodes solid crust of electrolyte insulation molten aluminium oxide molten aluminium tapping hole carbon lining of cell (cathode) + - Making aluminium by electrolysis

2 All metals conduct electricity when solid and when liquid. 3 All metals corrode in moist air. Metal properties and uses – true or false? 1 All metals are strong in tension.

Which properties of metals does this illustrate?

Which properties of metals does this illustrate?

2 The bonding between metal atoms is strong. 3 An electric current in a metal is a flow of electrons. Metal structure and bonding – true or false? 1 Metals are made up of molecules.

In a metal crystal the atoms are packed as close together as possible. This is a giant structure.

In a metal crystal the atoms are packed as close together as possible.

This is a giant structure.

Metallic bonding is strong bonding. Each metal atom contributes one or two electrons to a shared ‘sea’ of electrons. The shared bonding electrons can move through the whole metal structure.

Metallic bonding is strong bonding.

Each metal atom contributes one or two electrons to a shared ‘sea’ of electrons.

The shared bonding electrons can move through the whole metal structure.

2 Recycling rates are higher for metals than most other materials. 3 Recycled steel is not as strong as new steel. Metal waste and recycling – true or false? 1 Iron is the only metal that can be recycled economically.

What are the economic and environmental benefits of recycling iron?

What are the economic and environmental benefits of recycling aluminium?

LEARNING OBJECTIVES L12 understand that solid ionic compounds form crystals because the ions are arranged in a regular way. understand that the ions in a crystal are held together by the attraction between oppositely charged ions and that this is ionic bonding. understand how the physical properties in solid ionic compounds (melting point, boiling point and electrical conductivity) depend on their giant 3-D structures. know what happens to the ions when an ionic crystal dissolves in water and when salt evaporates and crystals form. know that solutions of ionic compounds conduct electricity because the ions are charged and able to move around independently in the solution. By the end of the lesson you should:

understand that solid ionic compounds form crystals because the ions are arranged in a regular way.

understand that the ions in a crystal are held together by the attraction between oppositely charged ions and that this is ionic bonding.

understand how the physical properties in solid ionic compounds (melting point, boiling point and electrical conductivity) depend on their giant 3-D structures.

know what happens to the ions when an ionic crystal dissolves in water and when salt evaporates and crystals form.

know that solutions of ionic compounds conduct electricity because the ions are charged and able to move around independently in the solution.

LEARNING OBJECTIVES L13 remember the properties of metals (limited to strength, malleability, melting point and electrical conductivity). be able to explain the properties of metals in terms of a giant structure of atoms held together by strong metallic bonding. understand that in a metal crystal there are positively charged ions held closely together by a sea of electrons that are free to move. By the end of the lesson you should:

remember the properties of metals (limited to strength, malleability, melting point and electrical conductivity).

be able to explain the properties of metals in terms of a giant structure of atoms held together by strong metallic bonding.

understand that in a metal crystal there are positively charged ions held closely together by a sea of electrons that are free to move.

Properties, structure, and bonding in four spheres

atmosphere hydrosphere biosphere lithosphere biosphere lithosphere In which of the four spheres are you likely to find . . . . . . simple molecular gases?

In which of the four spheres are you likely to find . . . . . . large covalent structures such as proteins? atmosphere hydrosphere biosphere lithosphere biosphere lithosphere

In which of the four spheres are you likely to find . . . . . . giant ionic structures such as sodium chloride? atmosphere hydrosphere biosphere lithosphere biosphere lithosphere

In which of the four spheres are you likely to find . . . . . . giant covalent structures? atmosphere hydrosphere biosphere lithosphere biosphere lithosphere

In which of the four spheres are you likely to find . . . . . . simple covalent molecular liquids? atmosphere hydrosphere biosphere lithosphere biosphere lithosphere

In which of the four spheres are you likely to find . . . . . . solid metals such as gold? atmosphere hydrosphere biosphere lithosphere biosphere lithosphere

A B C D Which of these four diagrams shows the best picture of the type of structure in . . . . . . nitrogen gas?

Which of these four diagrams shows the best picture of the type of structure in . . . . . gold? A B C D

Which of these four diagrams shows the best picture of the type of structure in . . . . . . silicon dioxide? A B C D

Which of these four diagrams shows the best picture of the type of structure in . . . . . . potassium chloride? A B C D

Which of these four diagrams shows the best picture of the type of structure in . . . . . . water? A B C D