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2.
The Magic of Chemical Reactions
Chemical equations :
Representation of chemical reaction with the help of chemical formulae is a
chemical equation.
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reactions. Ex : CuSO 4
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Types of chemical reactions :
Combination reaction : When two or more substances combine to form single
product, then the reaction is known as combination reaction.
Ex : Fe + S 
 Fes
Decomposition reaction : Those reactions in which a compound splits up into two
or more simpler substances are known as decomposition reactions.
Heat
Ex : CaCO 3 
 CaO + CO 2
Displacement reaction : When a more reactive element removes another element,
having less reactivity, from its compound. These reactions are termed as displacement

 ZnSO 4
+ Zn
+ Cu
Double displacement reactions :
The reactions where a precipitate is formed by change of ions between the
reactants, are double displacement reactions.
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Ex : AgNO 3
+
NaCl
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C

 AgCl +
NaNO 3
Oxidation and Reduction :
The chemical reaction in which reactants gain oxygen to form corresponding oxide
is known as oxidation reaction. Similarly the chemical reaction in which reactants
G
lose hydrogen to form product is also oxidation. Ex : C + 2H 2
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reduction. Ex : 2Cu + O 2

 2CuO
Redox reactions :
When oxidation and reduction take place simultaneously in a given chemical
reaction is known as redox reaction.
Ex :
Reduction
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
 CH 4
Chemical reactions in which reactants gain hydrogen are reduction reactions.
Similarly, the reaction in which reactants loose oxygen atom to form product is also
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BaSO 4
+ 4C

 BaS + 4CO
Oxidation
Rancidity :
The condition produced by aerial oxidation of fats and oils in foods marked by
unpleasant smell and taste is called rancidity.
Antioxidants are used to prevent oxidation food containing fats and oils. Storage of
food in air tight containers also retards oxidation.
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Unique
MCQ's
Neutralization :
Acids and bases in their aqueous solutions react with each other and produce salt and
water. This reaction is known as neutralization reaction.
Ex : NaOH + HCl


NaCl + H 2 O
MULTIPLE CHOICE QUESTIONS (MCQ's)
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(Each question carries one mark)
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MCQ's BASED ON PRACTICALS
Experiment : To perform and observe the following reactions and classify them into;
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To observe the reaction of water on quicklime :
a quicklime is added to water in a test tube b a lot of water is added to quicklime
c some water is sprinkled over quicklime d none of these
When crystal of ferrous sulphate are strongly heated, the residue obtained is :
a red in colour
c green in colour
b blue in colour
d colourless
When a solution of sodium, sulphate is treated with a solution of barium chloride, the
solution after reaction contains mainly :
a barium sulphate
c both
b sodium chloride
d none
Reaction of iron nails with copper solution is an example of :
a combination reaction
b decomposition reaction
c displacement reaction
d double displacement reaction
Reddish brown deposit obtained on iron nails when kept in a solution of copper sulphate in
water is that of :
a Cu 2O
c Cu
b CuO
d CuS
When copper powder is strongly heated, a black substance is formed. Which is that
substance?
a copper oxide
c copper sulphate
b oxygen
d copper chloride
Which gas is formed when dil. H2SO4 is mixed with FeS?
a hydrogen
c sulphur
b oxygen
d hydrogen Sulphide
What is the odour of H2S gas?
a rotten egg
c odourless
b pungent smell
d smell of lemon
What type of chemical reaction take place when magnesium wire is burnt in air?
a decomposition reaction
b combination reaction
c displacement reaction
d double displacement reaction
What type of chemical reaction takes place when lime stone is heated?
a combination reaction
b decomposition reaction
c displacement reaction
d double displacement reaction
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(A) Combination Reaction
(B) Decomposition Reaction
(C) Displacement Reaction
(D) Double Displacement Reaction
i) Action of water on quick lime
ii) Action of heat on ferrous sulphate crystals
iii) Action of iron nails kept in copper sulphate solution
iv) Reaction between sodium sulphate and barium chloride solution.
The Magic of Chemical Reactions
SCIENCE & TECHNOLOGY - S.S.C.
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Which of the following is a displacement reaction?
a CaO
+ CO 2
c 2Mg
+ O2
Fe 2 O 3
+ 2Al

 CaCO 3
b 2Na

 2MgO

 Al 2 O 3
+ 2H 2 O
d 2K + Cl 2

 2NaOH + H 2

 2KCl
+ 2Fe . Name the type of reaction in the above example.
a combination reaction
c displacement reaction
b decomposition reaction
d double displacement reaction
What happens when dilute hydrochloric acid is added to iron filings?
a hydrogen gas and iron chloride are produced
b chlorine gas and iron hydroxide are produced
c no reaction takes place
d iron salt and water are produced
You are given potassium chromate solution. In order to obtain an orange precipitate what
should we mix in it?
a barium sulphate
c barium sulphide
b barium chloride
d copper sulphate
What is added to zinc sulphate solution to obtain a white precipitate?
a barium sulphide
b barium sulphate c copper sulphide
d iron sulphide
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MCQ's BASED ON CHAPTER
a H2
+ Cl 2
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
 2HCl
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+ Cl 2
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b H2
+ 2Cl 2 
 HCl
 2HCl
d 2H 2 + Cl 2 
What happens when silver chloride is exposed to sunlight?
a silver metal is formed
b no changes take place to silver chloride
c oxide of silver is formed
d sulphide of silver is formed
What is the chemical formula of Plaster of Paris (POP)?
a CaSO 4.H 2O
c C 6 H 12 O 6
b CuSO 4.5H 2O
d CaOCl 2
During reduction reaction :
a reactants gain oxygen
b reactants lose hydrogen
c reactants gain hydrogen
d reactants lose nitrogen
What is called the addition of oxygen to a substance?
a reduction reaction
b decomposition reaction
c oxidation reaction
d neutralization reaction
c H2
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
 HCl
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Which of the following is a physical change?
a ripening of fruit
b ice changes to water
c milk is set into curd
d rusting of iron
Hydrogen combines with chlorine to form hydrogen chloride. Which of the following is a
correct balanced equation for the above reaction ?
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Moderate Level
Elementary Level
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What is the product of the following chemical reaction?
C + 2H 2
a CH 4


b C 2H 2
c CH 6
The Magic of Chemical Reactions
d C 2H 4
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2.
3.
MCQ's
When hydrogen is heated with vegetable oil in the presence of powdered nickel as catalyst,
which product is formed?
a sugar
c carbohydrate
b fat
d glucose
In the reaction represented by the equation :
MnO 2 + 4HCl 
 MnCl 2 + 2H 2 O + Cl 2
What is the substance oxidised?
a MnO2
c Cl 2
b MnCl 2
d HCl
What type of reaction is Respiration?
a endothermic reaction
b exothermic reaction
c decomposition reaction
d double displacement reaction
Which substance is used to prevent oxidation of food containing fats and oils?
a sugar
c antioxidants
b oxygen
d common salt
What is the chemical formula of concrete?
a CaOCl 2
c CaO .Al 2O 3.6H 2O
b CaSO 4.H 2O
d CuSO 4.5H 2O
Which of the following has utilised silver chloride?
a crayons manufacturing
b making statues
c moulding in dentistry
d black and white photography
Which of the following chemical substance is used in crayons manufacturing?
a silver bromide
b plaster of Paris
c alumina
d calcium carbonate
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a KNO 3(s)
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
 CaO + CO 2
b NaOH (s)
+ H 2O(l)
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d C 12 H 22 O 11
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
 KNO 3(aq)

 NaOH (aq)

 12C + 11H 2 O
The chemical reaction between copper chloride and potassium iodide is characterised by :
a evolution of chlorine
b formation of brown precipitate of cupric iodide
c formation of white precipitate of cupric iodide
d formation of copper metal
How are food products containing fats and oils are packaged in order to prevent from
spoilage?
a oxygen
c nitrogen
b carbon dioxide
d hydrogen
Water is decomposed by:
a thermal decomposition
b electrolysis
light
c
d acid
Which of the following is decomposed by acid?
a CaS
c AgCl
b KCl
d NaCl
What is added to sodium chloride to get a white precipitate?
a silver nitrate solution
b potassium nitrate solution
c calcium nitrate solution
d barium nitrate solution
c CaCO 3
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+ H 2 O (l)
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In which type of reaction two compounds exchange their positive and negative radicals?
a combination reaction
b decomposition reaction
c displacement reaction
d double displacement reaction
Which of the following is an exothermic reaction?
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Complex Level
The Magic of Chemical Reactions
SCIENCE & TECHNOLOGY - S.S.C.
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Mysterious Level
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Answers
MCQ's BASED ON PRACTICALS
1
6
11
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c
a
b
2
7
12
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a
d
c
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b
a
a
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4
9
14
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c
b
a
5
10
15
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c
b
a
MCQ's BASED ON CHAPTER
Moderate Level
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Which of the following is not a correct chemical reaction?
a CuSO4 + Zn  ZnSO4 + Cu
b CuSO4 + Mg  MgSO4 + Cu
c CuSO 4 + Fe  FeSO 4 + Cu
d ZnSO 4 + Cu  CuSO 4 + Zn
Hint : Cu is less reactive than zinc. Hence, Cu cannot displace zinc from zinc sulphate.
When soap is scrubbed on a white cloth, where a yellow stain of curry is present, it
changes into reddish brown. This is due to:
a combination reaction
b decomposition reaction
c neutralization reaction
d displacement reaction
Hint : Turmeric present in curry is an indicator. It will turn reddish brown in basic solution
(soap is a basic solution).
Silver ornaments become dark on prolonged exposure to air. This is due to the formation of
layer of its:
a oxide
c carbonate
b hydride
d sulphide
Hint : Silver ornaments slowly combine with H 2S gas present in air to form black coating of
silver sulphide.
Which of the statements about the reaction below are incorrect?
2PbO(s) + C (s)  2Pb (s) + CO 2(g)
a lead is getting reduced
b carbon is getting oxidised
c lead oxide is getting oxidised
d none of these
Hint : The removal of oxygen from a substance is called reduction and addition of oxygen to
a substance is called oxidation.
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- b
- c
2
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b
3
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a
4
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a
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c
Elementary Level
1
6
- a
- c
2
7
-
b
d
3
8
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d
b
4
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b
5
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c
Complex Level
1
6
- d
- a
2
7
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b
a
3
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b
4
-
c
5
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b
Mysterious Level
1
- d
2
-
c
3
-
d
4
-
c
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The Magic of Chemical Reactions