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Activity Series

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Activity Series - Lesson Summary

The arrangement of metals in the decreasing order of their reactivity is known as activity series. In the activity series highly reactive metals placed at the top and least reactive metals placed at the bottom.

Gold placed at bottom of the series is the least reactive among the metals and potassium placed at the top is the highly reactive metal.  Hydrogen is the non-metal included iin order to compare the reactivity of metals.

The metal placed higher in the series can displace the other metal from its salt solution. Thus potassium can displace all other metals from their salt solutions.

Example: Potassium can displace hydrogen from the acids.
        2K + 2HCl →2KCl + H 2



Metals of low reactivity cannot displace high reactive metals from their salts. For this reason oxides of highly reactive metals like magnesium and aluminium are not reduced easily either by hydrogen, carbon or carbon monoxide. 
Metals that are placed below copper do not rust easily because of their low reactivity. 

Reactivity towards oxygen:
On moving down in the reactivity series the reactivity with oxygen decreases.
Metals like potassium, sodium, calcium, magnesium and aluminium can react with oxygen at room temperatures.

Potassium can react with oxygen to form its super oxide in addition to oxide.
K + O 2 → KO 2
4K + O 2 →  2K 2O

Sodium on reaction with oxygen forms metal oxide as well as metal peroxide.
4Na + O 2 → 2Na 2O
2Na + O 2 →  Na 2O 2

Calcium, magnesium and aluminum on reaction with oxygen forms their metal oxides.
2Ca + O 2 → 2CaO
2Mg + O 2 → 2MgO
4Al + 3O 2 → 2Al 2O 3

Reactivity towards water:
While moving down in the activity series the reactivity towards water decreases.
Potassium, sodium and calcium can reacts vigorously even with cold water with the liberation of hydrogen gas.
K + H 2O → KOH + H 2
Na + H 2O → NaOH + H 2
Ca + H 2O → Ca(OH) 2 + H 2

Magnesium reacts very slowly with cold water but can reacts vigorously with hot water to produce hydrogen gas

Mg + H 2O → MgO + H 2

Metals like aluminium, zinc and iron does not reacts with cold water or warm water but can reacts with hot steam.
2Al + H 2O → Al 2O 3 + H 2
Zn + H 2O → ZnO + H 2
3Fe + H 2O → Fe 3O 4 + H 2

Reactivity towards mineral acids:

The metals which are present above hydrogen in the reactivity series can reduce hydrogen ions from the acids like HCl and H 2SO 4. Reactivity decreases on moving down the group in the series.
Potassium, sodium reacts vigorously with dilute acids to liberate hydrogen gas.
K + 2HCl → 2KCl + H2
Na + 2HCl → 2NaCl + H2

Calcium, magnesium also reacts vigorously but slowly with acids libearating hydrogen gas.
Ca + 2HCl → CaCl 2 + H 2
Mg + 2HCl → MgCl 2 + H 2

Metals below to hydrogen in the series does not liberate hydrogen on reaction with concentrated or diluted acids.

Ore:
Metals are available in the form of their ores. 
Ore is a mineral which contains high percentage of metal from which a metal can be extracted most economically.



Methods of extraction of metals from ore  are based on the reactivity of metals.

Methods of extraction:
        •  Reduction
        •  Electrolysis

Reduction is the process of removal of oxygen for extraction of metals from their oxide ores. The common reducing agents used for reduction of metal oxides are:
        •  Carbon monoxide
        •  Carbon
        • Hydrogen

Examples:
During the extraction of iron from its oxide:
Iron oxide is reduced to iron by carbon monoxide.
      FeO + CO → Fe + CO 2

Iron oxide is reduced to iron using carbon as the reducing agent.
      FeO + C → Fe + CO

During the extraction of copper from its oxide:
Copper oxide is reduced to copper using carbon as the reducing agent.
      CuO + C → Cu + CO

Copper oxide is reduced to copper using hydrogen as the reducing agent.
      CuO + H 2 → Cu + H 2O

But oxides of potassium, sodium, lithium, barium,calcium, magnesium and aluminum cannot be reduced by using carbon, carbon monoxide and hydrogen because of their high affinity for oxygen.

Important ores of Aluminium:
        •  Bauxite: Chemial formula is:  Al 2O 3.2H 20
        •  Bauxite is the principal ore of aluminium.
        •  Corundum: Chemial formula is: Al 2O 3 
        •  Cryolite: Chemial formula is: Na 3AlF 6.

The extraction of aluminium from bauxite involves three steps:
        •  The purification of bauxite using Bayer’s process.
        •  The electrolytic reduction of anhydrous Al 2O 3 by Hall and Herault’s process.
        •  The last step is the purification of impure aluminium by Hoope’s process  

Aluminium is used in:
        •  Manufacture of automobile components
        •  Construction process
        •  Manufacture of electric wires
        •  Packing medicines and pharmaceutical products
        •  Manufacture of soft drink cans and espresso coffee makers
        •  Manufacture of utensils

Alloy:
An alloy is a homogeneous mixture of solid solution of two or more metals or metals with non-metals.

Duralumin is a light and tensile alloy of aluminium. Duralumin is used in the making of air craft frames, pressure cookers. 
Magnalium is an alloy of aluminium and magnesium. Magnalium is used in the making of balances because of its high structural strength and resistance to corrosion. It is also used in the making of optical instruments like cameras and microscopes due to its light weight and resistant to corrosion.

Some important alloys:

Name of  the Alloy Composition    Properties  Uses Brass Cu: 80%
Zn: 20% It is generally strong resistant to corrosion and easily moulded into different shapes. In making of utensils, pipes and radiator statues etc Bronze Cu: 90%
Sn: 10% It is very strong in nature and also posses good resistance property. In making of coins, ornaments, utensils and statues Stainless steel Fe: 82%
(Ni + Cr): 18 Resistant to water, air and alkalies. In making of surgical instruments, watches and utensils etc Magnalium Al: 95%
Mg: 5% Very light in weight and very hard in nature. In making light articles and physical balance etc Duralumin Al: 95%
Cu: 4%
Mn: 0.5% It is very strong in nature and very light in weight. And is resistant to corrrosion. In making parts of aeroplane and ship etc

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