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Matter and Industrial processes All notes

Definition of Matter

Matter is anything that occupies space and has a mass. They are all substances
that have mass and take up space because they have volume. All those things
around you are made of matter, so are you, as are the Earth and stars in the sky.

States of Matter

Matter exists in three physical states as all things in the universe exist as solid,
liquid or gas. These are the three states of matter. Temperature is very important
in deciding whether a substance exists as a solid, liquid or a gas. Think about the
normal temperatures of where you live. The temperature of the air may freeze
water in winter but very rarely reaches 50 degrees Celsius in summer. This range
of temperature means that the solids, liquids and gases in the world will not
normally change from one state to another. When a solid, liquid or a gas is exposed
to very high or very low temperatures, it can change to another state. Raising the
temperature of a solid to its melting point will turn it into a liquid. Iron, for
example, is normally a solid but deep in the Earth’s crust it is so hot the iron is a
molten liquid. Lowering the temperature of a gas to its liquefaction point will turn
it into a liquid. Oxygen, for example, is normally a gas, but scientists can lower its
temperature to -183 degrees Celsius so that it can be turned into a liquid.

The Kinetic Theory of matter

This theory states that matter is made up of small particles which are in a
constant state of motion. The energy that causes the particles to move is kinetic
energy.

 In solids, the particles are vibrating around their fixed positions and have a
small amount of kinetic energy.
 In liquids, the particles contain more kinetic energy and are therefore
further apart. The particles are free to move but are not independent of
each other.
  In gases, the particles have maximum kinetic energy and move about more
freely.

Change of state

 If temperature is increased or reduced, matter changes its state. This is

because a temperature change will affect the amount of kinetic energy.
 If a solid is heated, the energy will make the particles vibrate faster until
the forces that hold them together are weakened and the particles move
apart. At this point, the solid has become a liquid.
 If a gas cools, the particles lose energy and come closer together. Eventually
strong forces develop between them and the gas turns into a liquid.
 All changes in state involve an increase in kinetic energy or a decrease in
kinetic energy caused by changes in temperature.

Summary of changes in state

The changes in state are summarized in the diagram below;

Heating and cooling substances

Different substances behave differently when subjected to temperature changes.

Most substances move through the three states. If a solid is heated, it melts into
a liquid which will eventually evaporate into a gas if heating continues. However,
some substances will change direct from solid to gas if heated and from gas to
solid if cooled. E.g. iodine crystals and camphor

Summery Properties of matter

Solid Liquid Gases
Arrangement of Very closely Closely packed Far apart
Particles packed
Force of Strong force of Weak force of No attraction
attraction attraction attraction
between particles
Movement of Vibrate and rotate Relatively free to Free to move
particles about fixed move but not independently
positions independent
Rate of diffusion Very slow diffusion Slow diffusion Rapid diffusion
Amount of kinetic Very little kinetic More kinetic High kinetic energy
energy energy energy
compressibility Not compressible Not compressible Compressible
Shape Have definite No shape, take the No shape, take the
shape/rigid shape of the shape of the
container container and fill
the container
Volume Have definite Have definite No volume, fills up
volume volume any container

Heating and Cooling Curves

 Heating Curve Cooling Curve

Explanations

 When ice was melting, the temperature remained constant at 0⁰C for
sometime even though the ice blocks were being heated. The heat supplied
during melting was being used to give the solid particles enough energy to
overcome the forces holding them together, so the temperature of the ice
could not increase. This energy is called latent heat.
 During boiling, the temperature of the water remained constant at about
100⁰C. The heat applied was being used to overcome forces holding the liquid
particles together.
 During cooling, the temperature remained constant for some time as the
liquid was turning into ice.

NB: - on heating and cooling curves, those sections with constant temperature show
a change of state from one form to another. On the heating curve diagram above,
A represents melting and C represents evaporation. At B, the water is in the form
of a liquid.
Elements Compounds and Mixtures
The Structure of Atoms

Definition

An atom is the smallest particle of an element which takes place in a chemical

reaction.

Structure

An atom is made up of a very small dense nucleus which contains protons and
neutrons. The protons are positively charged while the neutrons have no charge.
The masses of a proton and a neutron are almost the same and these form the bulk
of the mass of an atom.

Electrons circle around the nucleus and define the volume of an atom. Electrons
have negative charges. The number of protons and electrons in a neutral atom are
the same, so an atom is electrically neutral. The mass of an electron is very small.
The number of protons in an atom is called the atomic number or the proton
number and is the same as the number of electrons. The sum of protons and
neutrons in an atom is called the mass number or nucleon number or atomic mass. It
is possible for an atom to have different numbers of protons and neutrons. In this
case, the atomic number is different from the atomic mass.

Physical and chemical changes

Physical changes: - these are changes in the physical properties (size, shape,
density) or state of matter without a change in composition. No new substances are
formed during physical changes. As water changes from liquid to ice, its
appearance changes but its chemical composition remains the same. If we heat
platinum wire in a burner flame, the wire will become red hot. It returns to its
original; silvery metallic form after cooling. The platinum undergoes a physical
change while under the flame but its composition remains the same under both
conditions.

Chemical changes: - these are changes to the chemical composition of a product

and a new substance is formed with entirely different composition from the
original material. If a clean copper wire is heated in a burner flame, a change in
appearance is noted when it cools. The copper no longer has its characteristic
color, but now appears black. The black material is copper ii oxide.

Examples of physical processes and chemical processes

Physical Chemical Processes
 Processes
1 evaporation 1 Burning
2 Filtration 2 electrolysis
3 Magnetism 3 Photosynthesis
4 Distillation 4 Respiration
5 Dissolving 5 rusting
6 Sieving,
winnowing
7 mixing

Elements
An elemnt is a substance made up of the same kind of atoms. Examples include
magnesium, sulphur, carbon, zinc, iron and copper. All known substances on earth
are formed from a chemical alphabet of 106 known elements.

Compounds
A compound is a substance formed from two or more elements which are chemically
joined together. Examples include water, carbon dioxide, sugar, magnesium oxide
etc.

Molecule

A molecule is the smallest unit of a compound formed by the bonding of two or

more atoms. It can not be subdivided further without destroying the compound.

Mixtures
A mixture is a physical combination of two or more substances which do not loose
their physical properties. E.g. air, soil, sulphur and iron, etc

Differences between compounds and mixtures

Compound Mixture
1 A new substance is formed 1 No new substance is formed
2 Properties of compound different 2 Individual substances retain their
from properties of its constituents properties
3 Heat is either taken in or given out 3 No heat
4 Substance can only be separated by 4 Substance can be separated by
 chemical means physical means
If we mix iron filings and sulphur powder, the iron in the mixture is uncombined
with the sulphur and will be attracted to a magnet. But if the mixture is heated,
the iron and the sulphur chemically combine to form iron sulphide which is not
attracted by a magnet. Iron sulphide is a compound which can only be separated by
chemical means.

Heat
Iron + sulphur Iron sulphide

Metals and Non Metals

Properties of metals and non Metals

Metals Non Metals

1 Solid at room temperature except for Can be solid, liquid or gas
mercury which is a liquid.
2 They have a luster or gloss which
means they shine when polished
3 Metals are good conductors of They are insulators except carbon
electricity
4 They are also good conductors of They are poor conductors of heat i.e.
heat they are good insulators of heat
5 Most metals are malleable (can be Not malleable and not ductile
hammered into sheets) and they are
ductile (they can be drawn into wire)
6 Metals have high melting points and Have low melting points
high densities
7 Metals have a high tensile strength Have low tensile strength

Examples
Metals Non Metals
1 Potassium Carbon
2 Calcium Phosphorous
3 Sodium Oxygen
4 Iron Nitrogen
5 Zinc Water
6 Copper Sulphur
7 Gold Iodine

The reactivity of metals

Reactions of metals with oxygen

Most metals burn in air to form basic alkaline oxides i.e.

Metal + Oxygen Metal oxide

Examples;
Magnesium + oxygen magnesium oxide
Calcium + oxygen calcium oxide, and
Iron + oxygen iron oxide

When these oxides are dissolved in water they form bases, which are alkaline solutions
which turn red litmus paper to blue and have a pH above 7. Magnesium oxide becomes
magnesium hydroxide when dissolved in water. Calcium oxide becomes calcium hydroxide
solution.

Magnesium oxide + water magnesium hydroxide

Reaction of metals with water

Metals react with water to form an oxide and the process releases hydrogen gas. i.e.

Metal + Water Metal oxide + Hydrogen

Examples;
Iron + Water Iron oxide + Hydrogen
Zinc + Water Zinc oxide + Hydrogen
Calcium + Water Calcium oxide + Hydrogen
Magnesium + Water Magnesium oxide + Hydrogen

Water is made up of Hydrogen and oxygen (H₂O). The oxygen in water will react with the
metal to form the metal oxide releasing the hydrogen as gas. Where the metal is more
reactive as in the case of potassium, sodium and magnesium, the oxide readily dissolves in
the water to form a hydroxide as below;

Potassium + Water Potassium hydroxide.

Important: - some metals do not react with water at all and this will be discussed below.

Reactions of metals with acids.

Metals react with acids to form a salt and release hydrogen gas.
Metal + Acid Salt + Hydrogen

The name of the salt formed depends on the type of acid used. Sulphuric acid produces
sulphates and hydrochloric acid produces chlorides. Examples are given below;

Iron + Sulphuric acid Iron sulphate + hydrogen

Iron + Hydrochloric acid Iron ii chloride + hydrogen
The Reactivity Series
It is the arrangement of metals in order of their reactivity from the most reactive to the
least reactive. For the purposes of our syllugbus, the metals are arranged according to
their reactivity with air(oxygen), water and acids.

Metal Reaction with Reaction with Reaction with

Oxygen water or steam acid
Most Potassium Form oxides even React with cold Violent
reactive Sodium without heating water reaction
Calcium
Magnesium Burn to form React with steam React with
Aluminum oxide dilute acid
Zinc
Iron Reacts slowly Slow reaction Reacts with
 with steam dilute acid

Lead Slow reaction at Slow reaction No reaction

the surface with steam at
the surface
Copper Slow reaction at No reaction No reaction
Least the surface
reactive

Aluminum is a more reactive metal than iron and zinc, yet in experiments it may be
reluctant to react. This is because it has a jacket of aluminum oxide which is impenetrable
to water and air and so protects the metal. The reactions of potassium and sodium with
acids are very violent and extreme care is needed when carrying out experiments
preferably out doors.
Examples of chemical reactions
Displacement Reactions
This is a reaction in which an element replaces another during a chemical reaction. If iron
filings are put in copper ii sulphate solution which is blue in colour, the iron will replace
copper in the copper sulphate solution. i.e.

Iron + Copper ii sulphate solution Copper + Iron Sulphate

solution.

The iron replaces copper in the copper sulphate solution and the blue copper sulphate
turns green in colour. Brown copper is formed. If an iron nail is used, the nail becomes
coated with copper while the blue copper sulphate turns green.
If zinc is added to magnesium sulphate, nothing happens as magnesium is more reactive and
can not be replaced by a less reactive metal.
Examples of displacement reactions
Zinc + copper (ii) sulphate Solution Copper + Zinc sulphate
Lead + copper (ii) sulphate Solution Copper + lead sulphate
Magnesium + copper (ii) oxide Copper + magnesium oxide

Oxidation
It is a chemical reaction in which a substance gains oxygen or looses hydrogen. When
magnesium react with oxygen in air or in water to form magnesium oxide, we say it has
been oxidized. The oxidizing agent is the source of the oxygen which is the air or the
water. Most chemical reactions between metals and air where oxides are formed are
oxidation processes
Examples
1. Addition of oxygen to magnesium to form an oxide
Magnesium + oxygen magnesium oxide
2. Removal of hydrogen
Hydrogen sulphide + chlorine sulphur + hydrogen chloride
Hydrogen has been removed from hydrogen sulphide so we say it has been oxidized.

Reduction
It is a chemical reaction in which a substance looses oxygen or gains hydrogen. The
reducing agent is the substance which is being used to snatch away the oxygen or to
provide the hydrogen.
Examples of reducing agents
1. A metal higher in the reactivity series
Iron oxide + Magnesium magnesium oxide + Iron.
In this case, magnesium is more reactive than iron because it is higher up in the
reactivity series. It will therefore snatch away oxygen from iron oxide as it readily
reacts with oxygen than does iron.

2. Carbon
Iron oxide + Carbon carbon dioxide + Iron.
In this case carbon has a greater affinity for oxygen than iron and will readily
snatch away the oxygen in iron oxide leaving iron.
3. Hydrogen
If hydrogen is added to a substance we also call that reduction
Hydrogen sulphide + chlorine sulphur + hydrogen chloride
The hydrogen has been added to chlorine so we say the chlorine has been reduced.

NB: reactions in which both reduction and oxidation occur at the same time are
called Redox reactions. Examples are in italics and bolded above.
Acids, Bases and Salts
Acids
Acids are solution of non metallic oxides. When oxides of non metals dislove in water, they
form acids. Other acids occur naturally in plants and animals. Examples include tartaric
acid in grapes, citric acid in lemons and acetic acid in vivegar.
Making acids
Simply dissolving oxides of non metals in water,
Examples;
1. Carbon dioxide a gas dissolves in water to form carbonic acid
2. Sulphur dioxide a gas dissolves in water to form sulphorous acid
3. Sulphur trioxide a white solid dissolves in water to form sulphuric acid
4. Nitrogen dioxide a brown gas, dissolves in water to form nitric acid
Bases
Bases can be made in one of two ways
1. by dissolving oxides of metals in water e.g. magnesium oxide dissolved in water to
give magnesium hydroxide which is a base, or
2. by adding water to reactive metals e.g. when you put sodium in water it reacts to
form sodium hydroxide. Another metal which can be used is potassium.

Properties of Acids and Bases

Acids Bases
1 Has a sour taste(never taste it) Has a bitter taste and slippery feel
between fingers
2 Turns blue litmus paper red Turns red litmus paper blue
3 They are corrosive Some bases are caustic
4 Reacts with base to form salt and water Reacts with acid to form salt and water
5 Turn universal indicator yellow, orange They turn universal indicator green, blue,
or red purple
6 They react with metals to produce salt
and hydrogen
7

Neutralisation and the formation of salts

Neutralisation is a chemical reaction between an acid and a base. An acid and a base will
neutralize each other. In this chemical reaction the hydrogen in an acid is replaced with a
metal to form a salt and water.
Formation of Salts
Salts can be formed in one of the following ways;
1. Acid + Base Salt + Water
Examples;
Hydrochloric acid + sodium hydroxide sodium chloride + water
Magnesium Hydroxide + Sulphuric Acid Magnesium sulphate + water
2. Acid + Carbonate Salt + water + carbon dioxide
Hydrochloric acid + calcium Carbonate calcium chloride + water + carbon
Dioxide
Sulphuric acid + Magnesium carbonate magnesium sulphate + water
+carbon dioxide

3. Acid + Metal salt + hydrogen

Iron + Sulphuric acid Iron sulphate + hydrogen
Iron + Hydrochloric acid Iron ii chloride +hydrogen

Speed of Chemical Reactions

Every chemical reaction has a rate or speed at which it occurs. There are various
conditions which affect the rate of chemical reactions.

Factors affecting the rate of chemical reactions

Factor Effect
1 Temperature(liquids, An increase in temperature increases the rate of chemical
solids and gases) reaction since particles gain more kinetic energy thus increasing
the chance of bonding.
2 Surface area The smaller or finer the particles of the reactants, the greater
(solids) the surface area exposed to a chemical reaction. This speeds up
the rate of the reaction. 10kgs of small twigs burns faster than
10kgs of big logs for this reason.
3 Concentration A greater concentration increases the number of particles
(liquids) available for a chemical reaction which increases the chances of
bonding. This increases the rate of a chemical reaction. 50%
dilute sulphuric acid will corrode things faster than 5% dilute
acid for this reason.
4 Pressure (gases) Increasing the pressure in a gas brings the particles close
together and therefore increases the chance of bonding. This
 speeds up the rate of a chemical reaction.
5 Catalyst (Liquids, A catalyst speeds up a chemical reaction by providing a
solids and gases) conducive environment which promotes the bonding of the
reactants. The catalyst itself is not affected during the
chemical reaction.

Reversible reactions
A reversible reaction is a chemical reaction that goes in either direction. E.g.
Sulphur dioxide + Oxygen Sulphur trioxide

The above equation demonstrates that sulphur trioxide is formed when sulphur dioxide is
reacted with oxygen. However, the sulphur trioxide immediately breaks down back to
sulphur dioxide and oxygen especially in the absence of a catalyst and other optimum
conditions like temperature and pressure.

The production of Iron and Steel

Occurrence of Iron
Iron occurs as iron oxide, a combination of iron and oxygen. The iron oxide is commonly
known as iron ore and is a common rock from the rusty brown soil is derived.
In Zimbabwe iron ore in mined at Redcliff in Kwekwe and extra ore is railed in from
Buchwa mine in Mberengwa. The area also has deposits of limestone which are used during
the extraction process of iron.
The Zimbabwe Iron and Steel Company (ZISCO) is located near these iron ore deposits
and is well served with a rail system which brings in coal from Hwange and an electrical
grid system which brings electricity from Kariba and Hwange.

Raw materials needed in the extraction of iron from ore

1. Iron ore – an oxide of iron and oxygen known as iron (iii) oxide to be broken or
reduced to get iron.
2. Coke – This will act as the reducing agent as well as being the fuel in the blast
furnace.
3. Limestone – it acts as a flux which reacts with impurities making it possible to
separate them from the iron
4. Hot air containing oxygen is blasted into the furnace which initiates and supports
the burning process.
The blast furnace
Iron is extracted from its ore by smelting in a blast furnace. It is a tall structure which
operates as an oven. Hot air is blown through the furnace to produce very high
temperatures. The furnace is then filled with iron ore, coke and limestone. The coke is
ignited and increases the temperatures in the furnace which smelts the iron ore and
limestone.

Diagram of blast furnace

Chemical reactions in the blast furnace

1. Coke is ignited by the hot air being blast into the furnace. This occurs near the
bottom of the furnace near the hot air tuyers.
Carbon + Oxygen Carbon dioxide + Heat
2. Carbon dioxide is reduced by coke
Carbon + carbon dioxide Carbon monoxide
3. Some iron ore is reduced by the carbon in coke. This is called direct reduction. This
occurs in the middle of the furnace.
Iron (iii) oxide + Carbon (coke) Iron + Carbon Monoxide
4. The bulk of iron ore is reduced by carbon monoxide produced in 2 and 3 above. This
is called indirect reduction. This occurs higher up in the furnace.
Iron (iii) oxide + Carbon monoxide Iron + Carbon dioxide
5. Limestone, also known as calcium carbonate is heated in the blast furnace and
breaks down into calcium oxide
 Calcium carbonate Calcium Oxide + carbon Dioxide
6. Calcium oxide reacts with the impurities in the blast furnace which are known as
silicone dioxide to form slag.
Calcium oxide + silica/silicone Dioxide Calcium Silicate (slag)
NB: the molten iron produced flows down to the bottom of the furnace where
it is tapped out. The slag is lighter in weight and therefore it floats on top of
the iron and is tapped out through a separate outlet.

Products from the blast furnace

1. Pig iron: - this is the main product from the blast furnace. The iron is tough and
brittle because it has high carbon content, about 4% by mass. The metal also
expands upon solidification and is therefore used for cast iron objects such as
drain pipes, septic tank lids, engine blocks and coal and wood stoves. The iron is not
malleable and ductile so can not be used for many other purposes.
2. Slag: -this is a by product and is used for road surfacing and may also be used as a
cheap fertilizer.
NB: Production from the blast furnace is a continuous process. Coke limestone and
iron ore are being added all the time and molten iron is run off continuously. The
furnace is only stopped for maintenance work which may be once in five years.

The production of Steel

To make iron from the blast furnace usable for the bulk of commercial purposes, the
amount of carbon has to be reduced. This is achieved by taking molten pig iron to another
furnace known as the Oxygen Lance Furnace. In this furnace, oxygen is blown into the
molten iron and impurities such as carbon, phosphorous and sulphur burn into gaseous
oxides which easily escape. A purer iron called Mild steel or wrought iron is produced
which contains only 1% carbon. Mild steel is strong, malleable ductile and can be welded
and is therefore used for many commercial purposes. Mild steel is also mixed with other
metals to form alloys.
 No fuel is added to the oxygen lance furnace because the process the chemical
reaction caused by blowing oxygen into molten steel is exothermic. This means the
reaction produces its own heat and there is no need for a fuel.
 The oxygen lance process is a batch process. This means a batch of products are
manufactured at a time before adding more raw materials.
 Diagram of Oxygen lance furnace

Summery of Iron products

Metal Properties Uses
Pig Iron  Cheaper than steel  Steel manufacture
 Easy to mould  Kitchen stoves, drain
 Expands on solidification pipes, engine blocks, etc
 Hard but brittle
Mild Steel  Malleable  Railway lines
 Ductile  Beams and girders of all
 Can be welded kinds and sizes
 Strong under both  Blots and tool
tension and compression
 Stainless  Resist heat and acids  Cutlery
Steel  Resists rusting  Sink units

The Extraction of Copper

In Zimbabwe, copper is mined in the Chinhoyi area at Mhangura, Sheckleton and
Alaska Mines. It is also mined at Nyati mine near the midlands. The ore exist as a
compound of copper and sulphur known as copper sulphide or chalcopyrite. A good
ore may contain only 5% copper but it is worth mining because of the usefulness of
copper.

The extraction of copper from its ore

The process has the following six steps;
1. Crushing – the ore is crushed to a fine powder.
2. Concentration by floatation – the powdered ore is added to a large tank of oily water
and then air is blown into the mixture. This results in the formation of froth to which
ore sticks while impurities sink to the bottom.
3. Roasting – the ore is dried and heated strongly in air. The impurities such as sulphur,
arsenic and antimony are oxidized and escape as gases.
4. Smelting – the product of roasting is smelted with limestone in a reverbatory furnace.
Limestone decomposes to calcium oxide, which react with impurities to form slag. The
slag layer of impurities is tapped off. The product of smelting is known as Matte
Copper, a compound of copper and sulphur.
Smelting Furnace ( reverbatory furnace)
5. Converting – the matte copper is transferred in molten state to a converter. Hot air is
blown into the molten copper oxidizing the impurities which will escape as gases. Other
impurities like iron react with silica in the walls of the furnace and are oxidized to a
slag which is tapped out. The result of Converting is called blister copper because many
blisters form on its surface as gases escape.

Converting Furnace

6. Electrolytic refining of copper – the blister copper is molded into bars which are taken
to the electrolytic cell. The blister copper is the anode (+ve) while the cathode (-ve) is a
thin sheet of pure copper. The electrolyte is aqueous copper (ii) sulphate which is
acidified to improve electrical conductivity and to dissolve impurities. When the current
is switched on, the blister anode will loose electrons to the circuit. Positively charged
Copper ions will be released into the electrolyte and the blister anode slowly dissolves.
Dissolution continues and this means the blister copper sheet will decrease in weight.
Impurities in blister copper fall to the bottom of the tank. The positively charged
 copper ions which have entered the electrolyte are attracted to the negative cathode.
They gain back their electrons through the electrical circuit and become copper atoms.
The copper is deposited on the cathode which gradually increases in mass. The copper
collecting at the cathode is pure as the impurities have fallen to the bottom of the tank
Diagram electrolytic cell

The properties and uses of Copper

1. Copper is a good conductor of electricity so it is used to make wirings and contacts for
the electrical industry.
2. It is a good conductor of heat so it is used in the manufacture of hot water pipes, solar
water heaters, car radiators etc
3. Copper shines when polished and is used in the manufacture of ornaments and jewellery
4. Copper does not rust and it is used in the construction industry and to make coins.
5. It alloys well with other metals and it is used to make bronze and brass.
Alloys of Copper
Alloy Properties Uses
Brass (Copper + Zinc)  Resists corrosion  Water taps, screws
 Is shiny  Ornaments
 Resonant  Musical instruments
 soft  Bullet catridges

Bronze (Copper + Tin)  Hard and Durable  Machinery bearings

 Resists corrosion  Bronzing of statues
 Resonant  Making springs, bells,
coins and medals
Coating processes
Coating means covering a metal with another substance.

Reasons for coating

1. To protect metals from corrssion/rusting because most metals rust when they
come into contact with air and water.
2. Metals are also coated to give them a decorative finish.
Coating methods
1. Painting – involves applying a thin coat of paint which will not allow both air and
water from coming onto contact with the metal. Painting also gives a decorative
finish.
2. Oiling – used on movable parts where painting would not last. Oiling keeps water and
air away from the metal as well as acting as a lubricant. E.g. bicycle chains, engine
pistons etc
3. Galvanizing – the coating of iron and steel with zinc. The iron is dipped into molten
zinc and the dried. The zinc layer provides a sacrificial layer because zinc is more
reactive than the iron. Oxygen will react with the zinc instead of reacting with the
iron. The zinc oxide produced forms a protective layer on the iron protecting it
from rusting.
4. Alloying – involves mixing iron with corrosive resistant metals producing an alloy
which does not rust. Iron is mixed with chrome and nickel to produce stainless steel
which is corrosive resistant even if it is scratched or broken
5. Electroplating – is a method of coating iron or steel by another metal which is
corrosion resistant using electricity.
Examples of metals used in electroplating
Metal Uses
Chrome  Decorative finish in motor vehicles
Copper  Protecting parts of steel before hardening
 As a base for other coating processes
 Cheap jewellery
Gold  Decorative finish for jewellery
 High quality electrical contacts
Nickel  Decorative finish for jewellery
 High quality electrical contacts
Silver  Decorative finish
 A tough base for chrome plating
Tin 1. Used in tin cans for food storage
Zinc 2. Cheap coating to prevent corrosion on steel products

The procedure copper plating

1. The metal to be coated is cleaned by placing it in a bath of concentrated
hydrochloric acid. This removes any corroded metal which may continue to corrode
while under the new coating.
2. An electrolytic cell is constructed as below
o Electrolyte -------- copper sulphate solution /copper
chloride/copper cyanide. The electrolyte is acidified and contains copper
ions which are positively charge.
o Electrodes
 Anode ----- pure copper
 Cathode ----- the item to be coated
3. When the circuit is switched on, the copper anode looses electron to the circuit
releasing positively charged copper ions to the electrolyte. In this process, the
anode dissolves.
4. The copper ions are attracted to the negative cathode where they gain back their
electrons from the circuit. They form copper atoms and form a thin layer of copper
metal firmly attached to the item to be plated.
Diagram electrolytic cell
Industrial Gases

Obtaining oxygen, nitrogen and carbon dioxide from the air

Air is a mixture of gases and these gases can be separated by fractional distillation of air.
It is possible to separate the gases because when liquefied, they have different boiling
points.
Stages involved
1. The air is cleaned to remove dust and smoke by passing it through filters.
2. The air is cooled to -78⁰C. At 0⁰C water vapour solidified and at -56⁰C, carbon
dioxide solidified. These two are removed as they freeze as they would later block
the equipment if not removed.
3. The remaining gases are compressed to about 150 atmospheres and cooled. The
pressure is released rapidly causing temperatures to drop further. This process is
continued until the temperature reaches -200⁰C. At this temperature, oxygen and
nitrogen are liquid except the rare gases (neon and helium)
4. The liquefied air is piped to the fractionating tower where temperatures are
allowed to increase. At -196⁰C, nitrogen evaporates and is collected from the top of
the tower. Oxygen has a booing point of -183⁰C and remains as liquid in the tower
and is piped from below.

Products from fractional distillation of air

1. Carbon dioxide
2. Oxygen and
3. Nitrogen
Obtaining oxygen and hydrogen from the electrolysis of water
When a current is passed through a solution (electrolyte), chemical reactions occur at the
electrodes which break down the electrolyte. The electrolyte contains ions (charged
atoms) which carry current through the electrolyte.
Stages involved
1. An electrolytic cell is constructed as in the diagram below. The electrolyte is
acidified water. The acid is added to improve the electrical conductivity of the
water. This creates ions two kinds of ions in the water, hydroxyl ions (OH⁻) which
are negatively charged and hydrogen ions (H⁺) which are positively charged. The
electrodes are made of carbon or platinum because these do not react with the
acid.
2. When the current is switched on, negatively charged hydroxyl ions are attracted to
the positive anode where they loose electrons. They produce oxygen atoms which
bubble out as oxygen gas. Oxygen gas is therefore collected at the anode.
 3. Positively charged hydrogen ions are attracted to the negative cathode where they
gain electrons. They become hydrogen molecules and bubble out as hydrogen gas.
Hydrogen is therefore collected at the cathode.

Diagram electrolysis of water

Uses of industrial gases

Oxygen
1. Used in steel making in the oxygen lance process
2. Used for medical purposes
3. Used for cutting and welding purposes
Nitrogen
1. Used in the manufacture of ammonia
2. Used as a refrigerant e.g. to freeze vegetables
3. Used for medical purposes e.g. burning of growths on the skin
4. Used to preserve sperm for artificial insemination.
Carbon dioxide
1. Used for refrigeration as dry ice
2. Used in fire extinguishers
3. Used in fizzy drinks
Hydrogen
1. Bubbled through fat in the manufacture of margarine
2. Used in the manufacture of ammonia

The production of Sulphuric acid

Sulphuric acid is an oily colorless liquid and when it is added to water it forms a very
strong acid. It is made using what is called the contact process at Zimphos near Harare.
Sources of raw materials
1. Oxygen from the air and
2. Iron sulphide alternatively known as iron pyrites, an ore of iron mined in Zimbabwe.

Optimum conditions in the production of Sulphuric acid

1. High temperatures of around 450⁰C
2. Passing the gasses through several beds of vanadium (v) oxide, a catalyst.
Stages in the productions of sulphuric acid: the Contact Process
Stage 1: production of sulphur dioxide
Sulphur dioxide can be produced by burning sulphur in air. In Zimbabwe it is more
convenient and cheaper to produce it by burning an ore of iron known as iron pyrites. It is
a compound of iron and sulphur. (Iron sulphide)
Iron Pyrites + Oxygen sulphur dioxide + iron oxide
Stage 2: Production of sulphur trioxide
Sulphur dioxide is mixed with oxygen and pumped into a reaction chamber. In this chamber
temperatures are controlled around 450⁰C and vanadium (v) oxide is added as a catalyst.
Under these conditions sulphur dioxide is oxidized to sulphur trioxide in a reversible
reaction. This is the contact process.
450⁰C
Sulphur dioxide + oxygen Sulphur trioxide
Vanadium (v) oxide
Stage 3: Absorption process:- Production of Oleum
The sulphur trioxide is cooled and then absorbed into concentrated sulphuric acid in an
absorption tower to produce Oleum (fuming sulphuric acid).

Sulphur Trioxide + Sulphuric Acid Oleum

Sulphur trioxide could be dissolved in water to produce sulphuric acid but the heat of the
chemical reaction would produce a mist of sulphuric acid which would be difficult to
condense and dangerous to health.
Stage 4: Dilution process:- production of sulphuric Acid
When sulphuric acid is needed, oleum is added to water. The strength of the acid depends
on the amount of oleum added.
Oleum + Water Sulphuric acid

Diagram: process of producing sulphuric acid

Industrial uses of sulphuric acid

1. Used in the manufacture of fertilizers, mainly super phosphate
2. Used in the manufacture of aluminum sulphate, a flocculent used in the purification
of water.
3. It is used in the extraction of metals
4. For cleaning metals before electroplating
5. In the manufacture of textiles
6. As an electrolyte in car batteries
7. In paper making
8. In the manufacture of detergents
9. It is also used as a drying agent
10. It is used in the manufacture of plastics
11. It is used in the manufacture of dyes, soaps, explosives and in refining oil.

The Production of Ammonia

Ammonia is a colorless gas which can be recognized by its choking smell. It dissolves easily
in water to give an alkaline solution. Ammonia is the only alkaline gas (base) and reacts with
acids to salts which are useful in industry. In Zimbabwe Ammonia is produced by Sable
Chemical Industries in Kwekwe.

Sources of inputs
Ammonia is produced by reacting hydrogen and nitrogen
 Hydrogen is produced from the electrolysis of water from the Sebakwe River in
Kwekwe.
 Nitrogen is produced from the fractional distillation of air.

Stages in the production of Ammonia: The Haber Process

Stage 1: The Mixing chamber: - hydrogen and Nitrogen are mixed in the ration 1:3 in the
mixing chamber.
Stage 2: The Reaction Chamber: - the gases are passed to the reaction chamber where
they are compressed to a pressure of about 200 atmospheres. The temperature in the
reaction chamber is about 450⁰C and there are iron filings acting as a catalyst. Under
these conditions the nitrogen and hydrogen combine in a reversible reaction to form
ammonia. Only about 20% of the mixture of gases is converted into ammonia.
450⁰C & 200 atms
Nitrogen + Hydrogen Ammonia + Heat
Iron Catalyst
Stage 3: The Cooler: - the ammonia produced is removed from the mixture by
condensation in the cooler. The unconverted gases are mixed with more hydrogen and
nitrogen and recirculated through the reaction chamber.
Diagram: production of ammonia
Optimum conditions for the production of Ammonia
1. High pressure of between 200 to 300 atmospheres
2. Temperatures ranging from 450 to 500⁰C as ammonia will start breaking down back
to hydrogen and nitrogen at very high temperatures.
3. A catalyst of iron
Uses of ammonia
1. Fertilizers e.g. Ammonium Nitrate
2. In the production of Nitric acid
3. Used for water purification
4. Used in the manufacture of drugs, explosives, man made fibers and dyes
5. Used as a refrigerant

Production of Nitric Acid

When pure, Nitric Acid is a colorless oily liquid but when allowed to stand, some of the
nitric acid decomposes giving the acid a yellow brown color. It is a very strong acid, a
powerful oxidizing agent and reacts with nearly all metals and with other organic
compounds such as skin and wood.

Sources of raw materials

1. Ammonia from the Haber process
2. Oxygen from the fractional distillation of air or from the electrolysis of water

Stages in the production of Nitric acid: The Oxidation Process

Stage 1: Production of Nitrogen dioxide
Ammonia is oxidized into nitrogen dioxide in the presence of a platinum/rhodium catalyst
at 900⁰C.

Platinum/rhodium
Ammonia + Oxygen Nitrogen dioxide + Water + Heat
900⁰C
This reaction is exorthemic, so the nitrogen dioxide is cooled to about 150⁰C before being
passed to the next stage.

Stage 2: Production of Nitric Acid

The nitrogen dioxide is further oxidized into Nitric acid.

Nitrogen dioxide + oxygen + water Nitric Acid (dilute)

Stage 3: Concentration of the acid

The concentration of the acid produced in stage two is about 10% because it contains a lot
of water. Concentrated Nitric acid is obtained by fractional distillation of the dilute
solution.
Diagram: production of Nitric acid

The Manufacture of Fertilizer

Ammonium nitrate is manufactured by sable chemical industries where both raw materials
are produced. In this process, ammonia gas is bubbled through 65% Nitric acid. The
ammonium nitrate in produced in solution and it is crystallized into granules.

Industrial interdependence
ZESA, ZISCO, Sable Chemicals, NRZ, Hwange e.t.c are companies which rely on each other
for their operations. For Oxygen and hydrogen to be separated electrolytically, electrical
energy is required from ZESA’s power generation at Kariba and Hwange power station.
ZISCO steel in turn requires oxygen for the lance process from Sable chemicals as well as
power from ZESA. Rail and road transport networks have a role in the interdependence
between these various companies.