Metals | Chemistry Form 4

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Metals - Chemistry Form 4

Rocks from which metals can be extracted are called ores. An ore is any naturally-occurring source of a metal that you can economically extract the metal from. Extraction of metals from their ores involves the following general process:


In this lesson we will discuss the occurrence and extraction of Sodium and Aluminium.



Sodium metal



Aluminium metal




Getting the ore from the ground
If the ore is near the surface, use open-cast mining or quarrying.
If it is deeper into the earth's crust, use deep mining.
2. Concentration of the ore
Froth floatation. This method is used when the percentage of mineral is used when the percentage of mineral in the ore is too small. In this process the ground ore is mixed with water and oil and air blown into the mixture.
Chemical leaching, the crushed ore is first dissolved in a chemical where only the ore can dissolve. It's filtered and the purified ore is crystallized ore is crystallized and the crystallized out of the filtrate.
Reduction of the ore to metal
There are two major methods of obtaining the metals from the use.
a.) Reduction by carbon
b.) Electrolysis

The following is a summary of the way metals can be obtained from their concentrated ores depending on their position in the electrochemical series.


Getting the ore from the ground

If the ore is near the surface, use open-cast mining or quarrying. If it is deeper into the earth's crust, use deep mining.
Concentration of the ore

Froth floatation. This method is used when the percentage of mineral is used when the percentage of mineral in the ore is too small. In this process the ground ore is mixed with water and oil and air blown into the mixture. Chemical leaching the crushed ore is first dissolved in a chemical where only the ore can dissolve. It's filtered and the purified ore is crystallized ore is crystallized and the crystallized out of the filtrate.
 

Reduction of the ore to metal
 

There are two major methods of obtaining the metals from the use.
a.) Reduction by carbon
b.) Electrolysis
The following is a summary of the way metals can be obtained from their concentrated ores depending on their position in the electrochemical series.

Sodium occurs chiefly as sodium chloride ,in sea water and salt lakes.
Sodium chloride is also found in deposition or rock salt.
Sodium is also found as a double salt,NaHCO3.Na2CO3.2H2O (Trona) in lake magadi and as sodium Nitrate deposition found in Chile.

Sodium metal is extracted by the downs process where molten sodium chloride is electrolysed. Calcium chloride is added to sodium chloride to lower the melting point of NaCl from 800oC to 600oC.The following video clip shows the electrolysis of molten sodium chloride. Courtesy of You Tube)


 

The animation below shows how Sodium metal is extracted using the Down's process.


During electrolysis sodium metal forms at the cathode where as chlorine gas form at the anode. A steel diaphragm is suspended between the electrodes to prevent sodium and chlorine from recombining.
Molten sodium is less dense than molten sodium chloride, hence it rises to than molten sodium chloride ,hence it rises to the top of the cathode from where it is removed periodically.
The liquid sodium is collected and solidifies and can be stored for use.


1. To make an alloy with lead which is used to manufacture tetraethyl lead, Pb(C2H5)4, an anti-knock addictive in petrol.
2. For the manufacture of sodium compound such as sodium cyanide (NaCN) used to extract gold and sodium peroxide Na2O2.
3. An alloy of sodium with potassium is used as a coolant in nuclear reaction.
4. Sodium vapor is used in sodium lamps which gives yellow-orange light.

The following are some of the uses of sodium

1.To make an alloy with lead which is used to manufacture tetraethyl lead, Pb(C2H5)4, an anti-knock addictive in petrol.
2. For the manufacture of sodium compound such as sodium cyanide (NaCN) used to extract gold and sodium peroxide Na2O2.
3. An alloy of sodium with potassium is used as a coolant in nuclear reaction.
4. Sodium vapor is used in sodium lamps which gives yellow-orange light.

Aluminium is usually extracted from bauxite The ore is first dissolved in hot aqueous sodium hydroxide where the iron impurities precipitate as iron(III)hydroxide The precipitate is filtered as iron (III) hydroxide


The filtrate is mainly Sodium aluminate [ NaAl(OH)4] . Aluminium hydroxide is precipitated by bubbling carbon (IV) oxide through the sodium aluminate filtrate. The product is filtered off and silicate impurities remain in solution.
Aluminum oxide residue is heated to give pure aluminium oxide.

The aluminum oxide is first heated .Aluminium oxide has a high melting ,point 20150C and a lot of heat would be needed to melt it. Hence the oxide is dissolved in cryolite (sodium aluminum fluoride Na3AlF6)whose melting point is 9000C,to lower melting point temperature of Al2O3 to about 8000C.The melt Al2O3 is then electrolyzed in a steel tank as shown below:


The following video clip shows how the electrolysis takes place.

Click to play the video and observe what happens carefully. (Courtesy of You Tube)


The melt is then electrolysed in a steel tank lined with graphite cathode & graphite rods dipped in the electrolyte serve as the anode.
The graphite lining is an inert electrode which prevents alloy formation.
During electrolysis aluminum is deposited at the cathode and oxygen is given off at the anode. Aluminium settles to the bottom of the cell and its tapped off at intervals. At this high temp, oxygen gas evolved reacts with carbon to form Carbon (IV) oxide and Carbon (II) oxide .this reaction bums away the anodes .the anode must therefore be replaced quite often.

Aluminium is used in the manufacture of various products. The following animation shows some of the uses of Aluminium.


In this lesson we will discuss extraction of Iron by reduction.


Iron is the most abundant metal ore in the earths crust. The main ore of iron are;

Reduction of Iron( III) Oxide is carried out in a blast furnace. A blast furnace is a huge structure more than 30 metres tall constructed of steel plates with heat resisting bricks. Click to play the following video to find out how a blast furnace works. (Courtesy of You Tube)

The raw materials are fed into the blast furnace from the top of the furnace, these include

a) Iron ore mainly Haematite Fe2O3
b) Coke -Carbon made from coal

c) Limestone- used to remove wastes

The iron ore, coke and limestone are heated by blasting in hot air at 6000C blown in from the bottom of the furnace.

The Ore is crushed and heated to remove water and other impurities with low melting point leaving behind 30 - 90% Iron ( III) oxide. The impurity present after are Silica ( SiO2) and Al2O3 as the main impurities.

Iron produced settles to the bottom of the furnace and melts at 15390C. The limestone helps in removal of impurities especially (Silica dioxide) and other acidic impurities in the ore to form liquid lag.
At 8000c the limestone decomposes to calcium oxide and carbon ( IV) oxide

CaCO3(s) CaO(s) + CO2(g)
The Carbon(II) Oxide formed after calcium carbonate decomposes is reduced by the coke to produce more carbon(II) Oxide which reduces more of the Iron Ore. The calcium Oxide with the other impurities to form slag.

CaO (s)+ SiO2(s) Ca SiO3(s)

Al2O3(s) + Ca0 (s) CaAl2O4(l)

The coke burns in the hot compressed air to form carbon( IV) oxide gas.

C(s) + O2(g) CO2(g) + heat
This reaction is highly exothermic and it raises the temperature to between 600 - 16000c.
The carbon( IV) oxide gas raises up and reacts with more coke (carbon) which reduces it to carbon (II)oxide (endothermic reaction).

CO2(g) + C(s) 2CO(g)
 

The Carbon(II)Oxide acts as reducing agent.

The carbon(II) Oxide formed reduces the Iron(III)Oxide to iron. This reaction takes place at the upper part of the furnace at temperature about 600 - 7000c

Fe2O3(s)+ CO(g) Fe(s) + CO2(g)

The molten slag is less dense and floats on top of molten iron preventing re-oxidation of the iron to iron III oxide by the hot air in the furnace

The iron obtained from the furnace is about 90- 95% pure and its called cast iron or pig iron.
It contains the following impurities carbon, sulphur, manganese, sulphur silicon and phosphorous. The impurities makes it brittle and cannot be welded, its used to make cookers, stoves railings, water pipes and not materials that require strength e.g. bridges. Impurities in the iron are removed by oxidation.

Wrought iron is the purest form of commercial iron and contains 99% of iron with only 0.1% carbon. Its not bristle like cast iron and can be welded and shaped by hammering (when hot) it malleable and ductile.

Most of the iron produced is converted to steel which is an alloy iron. An alloy is a uniform mixture of a metal with one or more other substances e.g. steel is an alloy of iron with carbon chromium and manganese. Majority of the iron produced in the blast furnace is converted into different steel alloys. The common alloys with some of their uses are given in the table below.


The main pollutants are carbon( IV) Oxide and sulphur (IV) Oxide. These gaseous products lead to serious air pollution. This may lead to formation of acid rain.

 


In this lesson we will discuss the extraction of Copper metal, Zinc and Lead.

Copper occurs in ores as copper pyrites which is mainly CuFeS2, Culprite Cu2O, Chalcocite Cu2S and Malachite CuCO3.Cu (OH)2

The most commonly used ore is copper pyrites, which is roasted in air to remove some of the sulphur.

2CuFeS(s) + 4O2 (g) Cu2S(s) + 3SO2 (g) + 2FeO(s)

Limestone and silica SiO2 are added and the mixture heated in the absence of air. The iron (II) oxide is converted into iron (II) silicate, FeSiO3, which constitutes the slag.
The slag separates itself from the copper (I) Sulphide. The copper (I) sulphide is then heated in a regulated supply of air where some of it is converted to copper (I) oxide which is then reduced to copper metal by the remaining copper (I) sulphide.

The copper obtained is 97.5% pure. The impurities are mainly iron,sulphur and traces of gold and silver. The impure copper is refined by electrolysis.

The ore is crushed into fine powder. It is mixed with water and an oil. Air is blown through the mixture and the concentrated ore collects in the froth. This method is known as froth floatation.

Click to play the following video to observe the process of froth floatation. (Courtesy of You Tube)


Copper (II) sulphate solution is used as the electrolyte.
During electrolysis, the copper anode dissolves into solution. The copper ions in the solution are reduced to copper metal at the cathode.
 

At the Anode

Cu(s) Cu2+(aq) + 2e-

At the cathode

Cu2+(aq) + 2e- Cu(s)

NOTE: The copper produced by this method is 99.98% pure. Traces of silver and gold collects as sludge at the bottom of the cell.

Strips of pure copper are used as the cathode whereas the anode is made of the impure copper as shown in the following video clip.

Click to play the following video clip to observe how this electrolysis takes place.(Courtesy of You Tube)


VO1:Making coins and ornaments VO2:Making alloys such as brass (Cu & Zn) Bronze (Cu & Sn) VO3:Making soldering instruments due to the high thermal conductivity VO4:Making electrical wires and contacts in switches plugs and sockets because copper is a good conductor of electricity

Zinc occurs in many parts of the world as calamine which is mainly Zinc Carbonate and Zinc blende which is mainly Zinc sulphate. In Kenya , Zinc blende is found at Kaloleni near Mombasa. It is found mixture of Zinc sulphate and lead (II) sulphate.

The ores are first roasted in air to form the metal oxides. If the ore roasted is Zinc blende then the oxides of lead and Zinc are formed.
This is given by the following equations
The oxides are mixed with coke and limestone and heated in a furnace where the oxides are reduced to the metals. The limestone decomposes to give Carbon (IV) oxide.
Equation

The Carbon (IV) oxide is reduced by coke to form Carbon (II) Oxide.
 

Equation

CO2(g) + C(s) 2CO(g)

Carbon (II) Oxide and coke are the reducing agents in the furnace.

The following equations show how this occurs.

Zinc exist as vapour form at the furnace temperature and leaves at the top of the furnace. The vapour is condensed in a spray of molten lead to prevent re-oxidation of Zinc. The solution of Zinc in molten lead is cooled further and the Zinc collects on the surface from where it is run off. Zinc can be purified by further distillation. The lead produced during the process is a liquid at the furnace temperature and trickles to the bottom of the furnace from where it may be tapped off.

VO1:Making the outer casing in dry batteries

VO2:Galvanized iron is made by dipping iron sheets into molten zinc

VO3:Ship Hull is made of steel
Zinc is sacrificed to protect the steel.

VO1:The major noise pollution from industries are from the vehicle operations within

VO2:Sulphur (IV) oxide is a major pollutant from metal industries Land pollution resulting from metal extraction is due to chemical waste disposal and mining. Outflow pipes from metal processing plants directly pour their waste into rivers and lakes

Air pollution is reduced by installation of scrubbers and electrostatic precipitators.
Water pollution is reduced by liquid wastes from plants being treated and reversed so that minimal amount is released to the rivers, streams and oceans.
Land pollution can be reduced by quarries and open trenches resulting from open cast mining being reclaimed by a process called landfill.
Noise pollution can be reduced by enforcing laws and governmental efforts to control nose pollution

Copper is used in the manufacture of various products. The following are some of the uses of Copper.

Zinc occurs in many parts of the world as calamine which is mainly Zinc Carbonate and Zinc blende which is  mainly Zinc sulphide. In Kenya , Zinc blende is found at Kaloleni near Mombasa. It is a mixture of Zinc sulphate and lead (II) sulphide.

The ores are first roasted in air to form the metal oxides. If the ore roasted is Zinc blende then the oxides of lead and Zinc are formed.


The oxides are mixed with coke and limestone and heated in a furnace where the oxides are reduced to the metals. The limestone decomposes to give Carbon (IV) oxide.

CaCO3(s)     CaO(s)  +  CO2(g)

The Carbon (IV)oxide is reduced by coke to form Carbon (II) Oxide.

CO2(g) + C(s) 2CO(g)

Carbon (II) Oxide and coke are the reducing agents in the furnace

.

Zinc exist as vapour form at the furnace temperature and leaves at the top of the furnace. The vapour is condensed in a spray of molten lead to prevent reoxidation of Zinc. The solution of Zinc in molten lead is cooled further and the Zinc collects on the surface where it runs off.

The following are some uses of Zinc

The major noise pollution from industries are from the vehicle operations within Sulphur (IV) oxide is a major pollutant from metal industries Land pollution resulting from metal extraction is due to chemical waste disposal and mining. Outflow pipes from metal processing plants directly pour their waste into rivers and lakes.

Air pollution is reduced by installation of scrubbers and electrostatic precipitators.
Water pollution is reduced by liquid wastes from plants being treated and reversed so that minimal amount is released to the rivers, streams and oceans.
Land pollution can be reduced by quarries and open trenches resulting from open cast mining being reclaimed by a process called landfill.
Noise pollution can be reduced by enforcing laws and governmental efforts to control nose pollution

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