Class 10; General Science Chapter 3

2. The most unreactive metals which are not affected
by air and water such as silver, gold and platinum are
generally found in free state in nature
Most metals however are found in combined state in
the form of their oxide, carbonate or sulphide etc.
Minerals The naturally occurring compounds of metals
along with other impurities are known as minerals
Ores The minerals from which metals are extracted
profitably and conveniently are called as ores

3. Gangue Ores contain metal compounds with
some of the impurities like soil, sand, rocky
material, etc. These impurities are called as
gangue
Metallurgy Metals can be extracted from the
ores by employing different separation
techniques. The process used for extraction of
metals in their pure form from their ores is
called metallurgy

4. Activity series
K
Na
Ca
Mg
Al
Zn
Fe
Pb
Cu
Hg
Ag
Au
Decreasing order of
reactivity
Top
↓
↓
↓
↓
↓
Bottom
The arrangement of metals in
the decreasing order of their
reactivity in the form of series
is called the reactivity series of
the metals
Thus the most reactive metal is
potassium and is placed in the
top of the list and least reactive
metal is gold which is placed
at the bottom of the list

5. Depending on the Chemical Reactivity, Metals
are divided into 4 categories. They are…
1. Highly Active Metals : They are extracted by Electrolysis.
For Example, Sodium, Potassium, Calcium etc.
2. Moderately Active Metals : These metals are extracted by
Reduction with Carbon. Example : Zinc, Iron etc
3. Lowly Active Metals : These metals can be extracted easily by
heating. Example : Copper, Mercury etc
4. Noble or Inactive Metals : They are found in free state.
Example : Gold, Silver etc

6. Extraction of Metals of High Reactivity
Metals which are high up in the reactivity series are very
reactive. For eg. sodium, potassium, calcium, aluminium,
etc. are the metals obtained by electrolytic reduction
Sodium, magnesium and calcium are obtained by
electrolysis of their molten chlorides
Sodium is extracted by electrolysis of fused sodium
chloride by Down’s process. Down's electrolytic cell,
consists of an iron container with a circular carbon
anode. The anode is surrounded by a ring shaped iron
cathode enclosed in a wire gauze which also acts as a
partition and separates the two electrodes.

7. On electrolysis, chlorine is liberated at the anode and
let out through an exit at the top.
Sodium is liberated at the cathode and remains in the
wire-gauze shell.
Level of molten sodium rises and it overflows into a
receiver.
2 NaCl -- > 2Na+ + 2Cl-
Anode
Reaction: 2Cl- → Cl2 + 2e-
Cathode
Reaction: 2Na+ + 2e- → 2Na

9. Extraction of metals of medium reactivity
The metals in the middle of activity series such as iron,
zinc, lead, etc. are moderately reactive.
These are usually present as sulphides or carbonates in
nature. It is easier to obtain a metal from its oxide, as
compared to their sulphides and carbonates.
The sulphide ores are first converted into oxides by
heating strongly in excess of air. This process is
known as roasting.
An example of roasting is when Zinc sulphide is converted into zinc oxide
by heating in presence of air.
2ZnS+3O2 —> 2ZnO + CO2

10. On the other hand, the carbonate ores are
changed to oxides by heating strongly in limited
air. This process is known as calcination.
The chemical reaction that takes place in
calcination of the Carbonate ore of Zinc is:
ZnCo3 —> ZnO + CO2
Similarly, Calcium Carbonate is converted to Calcium
Oxide by calcination as follows…
CaCo3 —> CaO + CO2

11. Zinc Oxide is then mixed with Coke (Carbon) and
ground into fine pieces and heated at 1673K in a
fire clay containers.
Here the Zinc Oxide gets reduced to metallic
Zinc. The carbon from coke acts as the reducing
agent in this reaction.
The reaction of the final step of extraction of zinc
is
2ZnO + C −−> 2Zn + CO2

12. Calcination Roasting
Calcination is a process in which
ore is heated in the absence of air
or in limited supply
Roasting involves heating of ore
lower than its melting point in the
presence of air or oxygen.
Calcination involves thermal
decomposition of carbonate ores.
Roasting is carried out mostly for
sulfide minerals.
During calcination, moisture is
driven out from an ore.
Roasting does not involve
dehydrating an ore.
Carbon dioxide is given out during
calcination
During roasting large amount of
toxic, metallic and acidic
compounds are released along with
Sulpher dioxide gas
Difference between Calcination & Roasting

13. Extraction of Metals of Low Reactivity
The metals at the bottom of the activity series are least
reactive. They are often found in free state e.g. gold,
silver and copper.
But copper and silver are also found in combined
state as their sulphide or oxide ores. For eg. copper is
found as Cu2S in nature and can be obtained from its
ore by just heating in air
2Cu2S + 3O2 (Heat) → 2Cu2O +2SO2
2Cu2O + Cu2S (Heat) → 6Cu+ SO2

14. Similarly, cinnabar (HgS) is an ore of
mercury. When it is heated in air, it is
first converted into mercuric oxide
(HgO).
Mercuric oxide is then reduced to
mercury on further heating
2HgS + 3O2 (Heat) → 2HgO +2SO2
2HgO +heat → 2Hg + O2

15. Refining of metals
The metals produced by various reduction processes
described above are not very pure. They contain
impurities, which should be removed, to obtain pure
metals. The most widely used method for refining
impure metals is electrolytic refining
For example, Cu (Copper) metal is purified
(Refined) by electrolysis.

16. A block of impure copper is taken as an anode or positive electrode.
Copper sulfate which is acidified with sulphuric acid is used as an
electrolyte along with pure copper tubes as a cathode or negative
electrode.
In this phase of electrolysis copper sulphate divides into a positive
ion of copper (Cu++) and a negative ion of sulfate (SO4— —).
The positive copper ion (Cu++) or cations travel towards the
negative electrode made of pure copper where it absorbs the
electrons from the cathode. Cu atom is deposited on the cathode

17. Refining of Copper

18. Corrosion of metals
Corrosion is degradation of materials due to reaction
with its environment. The major problem of corrosion
occurs with iron, since it is used as a structural
material in constructions, bridges, ship building,
automobile etc.
Example: When iron metal comes in contact with
oxygen present in moist air, a brown coat deposited
over it because of formation of iron oxide. This is
called rusting of iron.
When silver metal comes in contact with sulphur
present in air, a black coat is deposited over it because
of formation of silver sulphide. This is called corrosion
or tarnishing of silver.

19. Prevention of corrosion
Corrosion of metals can be prevented if the contact
between metal and air is cut off. This is done in a
number of ways. Some of the methods are given
below:
(1) Corrosion can be prevented if the metal is coated with
something which does not allow moisture and oxygen to
react with it
(2) Coating of metals with paint, oil, grease or varnish
prevents the corrosion of metals e. g rusting of iron can
be prevented by this method

20. 3) Coating of corrosive metals with non-corrosive
metals also prevents corrosion. Some of the methods
by which metals can be coated with non-corrosive
metals are:
Galvanizing: It is process of giving a thin coating of
zinc on iron or steel to protect them from corrosion.
e.g. shiny iron nails, pins, etc.
Tinning: It is the process of giving a coating of tin,
i.e., molten tin over other metal. e.g. Cooking vessels
made of copper and brass get a greenish coating due
to corrosion. This greenish coating is poisonous.
Therefore they are given a coating of tin to prevent
corrosion

21. ALLOY
An alloy is a homogeneous mixture of two or more
metallic solutions. Sometimes, in an alloy non-metals
can also be found.
The non-metals present in an alloy may be boron,
carbon, silicon or sulphur.
Alloys are harder and tougher than the base metal and
are resistant to corrosion.
They are inert to commonly used chemicals and are
magnetisable and ductile.

22. Name of the Alloy Composition Uses
Brass
Cu: 80%
Zn: 20%
In making of utensils, pipes and
radiator statues etc
Bronze
Cu: 90%
Sn: 10%
In making of coins, ornaments,
utensils and statues
Stainless steel
Fe: 82%
(Ni + Cr): 18
In making of surgical instruments,
watches and utensils etc
Magnalium
Al: 95%
Mg: 5%
In making light articles and
physical balance etc
Duralumin
Al: 95%
Cu: 4%
Mn: 0.5%
In making parts of aeroplane and
ship etc
German silver
Cu: 60%
Zn: 20%
Ni: 20%
It is useful in electroplating and
making of utensils
Gun metal
Cu: 88%
Sn: 10%
Zn: 2%
It is useful in making of guns,
machine parts and canons..etc
Solder metal
Pb: 50%
Sn: 50%
It is mainly useful to join electric
wires

23. In an alloy if one of the metals is mercury, then the
alloy is known as an amalgam
Pure gold, known as 24 carat gold and it is very soft. It
is, therefore, not suitable for making jewellery.
It is alloyed with either silver or copper to make it hard.
Generally, in India 22 carat gold is used for making
ornaments. It means that 22 parts of pure gold is
alloyed with 2 parts of either copper or silver

24. THANK YOU
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