ONE MARK QUESTIONS
C6H12O6
Q. 1. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas
collected over the other electrode.
[CBSE S.R 2018, CBSE 2009, 2012, 2013]
Ans : Water contains hydrogen and oxygen in the ratio of 2 : 1, that is why volume of H2 is double than that of oxygen.
Q. 2. What can be seen when a strip of copper metal is placed in a solution of silver nitrate? [CBSE 2015]
Ans :
The solution will become blue, shiny silver metal will get deposited.
Cu(s) + 2AgNOH3(aq) → Cu(NOH3)2 (aq) + 2Ag(s)
3. State one industrial application of reduction process.[CBSE 2015]
Ans :
It is used in the extraction of metals e.g., ZnO(s) + C(s) → Zn(s) + CO2(g)
4. Which one of the following is a chemical change? Give reason also.
(a) Burning of wax (b) Melting of wax [CBSE 2014]
Ans :
Burning of gas is a chemical change because new products with new properties will be formed on
burning.
5. Which one is a chemical change:
Rusting of iron or melting of iron?[CBSE 2014]
Ans : Rusting of iron is a chemical change.
6. State one basic difference between a physical change and a chemical change.[CBSE 2014, 2011]
Ans : In a physical change, no new substance is formed. In a chemical change, new substance(s) with new
properties is/are formed.
7. Name the oxidising and reducing agent in the following reaction:
CuO + H2 → Cu + H2O. [CBSE 2013]
Ans :
CuO is oxidising agent H2 is reducing agent.
8. Write a complete balanced chemical equation for the following reaction:. [CBSE 2013]
Sodium hydroxide + Sulphuric acid → Ans :
2NaOH + H2SO2 → Na2SO2 + 2H2O
9. Name and state the law which is kept in mind when we balance chemical equations. [CBSE 2012]
Ans :
Law of conservation of mass. It states Matter can neither be created nor be destroyed. The total mass
of reactants must be equal to total mass of products.
10. What is meant by a chemical reaction? [CBSE 2011]
Ans :
Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products
11. AgNO3(aq) + NaCl(aq) → AgCl ↓ + NaNO3(aq)FeS + H2SO4 → FeSO4 +H2S ↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↑ and ↓ ) along with the product. What do these two different arrows
indicate? [CBSE 2011]
Ans :
↑ shows evolution of gas, ↓ represents a precipitate.
12. Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water, a compound made up of hydrogen and oxygen is used to extinguish fire. Why? [CBSE 2011]
Ans : H2O is a compound constituted of hydrogen of oxygen elements and being a compound it has different
properties as compared to its constituting elements.
13. N2(g) + 3H2(g) → 2NH2(g),
name the type of reaction. [CBSE 2011]
Ans :
Combination reaction.
14. If copper metal is heated over a flame it develops a coating. What is the colour and composition of coating? [CBSE 2011]
Ans :
Black coloured coating is formed. It is a due to formation of copper oxide.
15. Write a balanced chemical equation to represent the following reaction: carbon monoxide reacts with hydrogen gas at 340 atm to form methyl alcohol.[CBSE 2011]
Ans :
CO(g) + 2H2(g) 340 → CH3OH(l)
16. Which one is a chemical change: fermentation of fruit juice or diluting fruit juice?[CBSE 2011]
Ans :
Fermentation of fruit juice is a chemical change.
17. Is burning of a candle wax a physical or a chemical change?
Ans :
Burning of a candle wax is a chemical change.
18. Write a balanced equation for the chemical reaction that can be characterised as precipitation reaction.[CBSE 2011]
Ans :
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
It is a precipitation reaction.
19. State the main difference between endothermic reaction and an exothermic reaction.[CBSE 2011]
Ans :
In endothermic reaction, heat is absorbed. In exothermic reaction, heat is evolved.
20. What happens chemically when quick lime is added to water filled in a bucket? [CBSE 2010, 2008]
Ans :
Calcium hydroxide (Slaked lime) is formed with evolution of heat and hissing sound.
CaO(s) + H2O(l) → Ca(OH)2(aq)
21. Define oxidation and reduction.
[CBSE 2011, 2010]
Ans : Oxidation is a process in which oxygen is added or loss of electrons take place. Reduction is a process in
which hydrogen is added or gain of electrons takes place.
22. Give an example of double displacement reaction (only with complete balanced equation).[CBSE 2011, 2010]
Ans :
BaCl2(aq) + H2SO4(dil.) $ BaSO4
(s) + 2HCl(aq)
It is a double displacement reaction.
23. On what basis is a chemical reaction balanced?
Ans :
Chemical equation is balanced on the basis of law of conservation of mass.
24. What change in colour is observed when white silver chloride is left exposed to sun¬light? State the type of chemical reaction in this change.
Ans : [CBSE 2010]
Grey coloured silver metal is formed and pungent smelling chlorine gas is evolved.
2AgCl(s) sunlight 2Ag(s) + Cl2(g)
It is photochemical decomposition reaction.
25. Write a balanced chemical equation for the reaction between sodium chloride and silver nitrate indicating the physical state of the reactants and the products.[CBSE 2010]
Ans :
( ) Silver Nitrate
AgNO aq NaCl aq AgCl s NaNO aq () () () ( ) Heat
3 + + 3
( ) Sodium Chloride ( ) Silver Chloride ( ) Sodium NItrate
26. Complete and balance the following equation:
Fe2O3 + Al $
Ans : [CBSE 2010]
Fe2O3 + 2Al $ 2Fe + Al2O3
27. Balance the following chemical equation:
Pb(NO3)2 $ PbO + NO2 + O2
Ans : [CBSE 2009]
2Pb(NO3)2 Heat 2PbO + 4NO2 + O2
28. Identity the type of reaction in the following example:
Na2SO4(aq) + BaCl2(aq) $ BaSO4
(s) + 2NaCl(ag)
Ans :
Double displacement reaction.
29. Identify the type of reaction in the following example:
Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s)
Ans :
Displacement reaction.
30. Identify the type of reaction in the following example:
2H2(g) + O2(g) $ 2H2O(l)
Ans :
Combination reaction.
31. Balance the given chemical equation:
Al(s) + CuCl2(aq) $ AlCl3(aq) + Cu(s)
Ans : [CBSE 2008(C)]
2Al(s) + 3CuCl2(aq) $ 2AlCl3
(aq) + 3Cu(s)
32. Balance the given chemical equation:
FeSO4(s) Heat Fe2O3(s) + SO2(g) + SO3(g)
Ans : [CBSE 2008]
2FeSO4(s) Heat Fe2O3(s) + SO2(g) + SO3(g)
33. Balance the following chemical equation:
Fe(s) + H2O(g) $ Fe3O4(s) + H2(g)
Ans :
3Fe(s) + 4H2O(g) $ Fe3O4(s) + 4H2(g)
34. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue green. Predict the new compound formed which imparts a blue green colour to the solution.
Ans :
CuO + 2HCl $ CuCl2 + 2H2O
Copper chloride solution imparts blue green colour to the solution.
35. Why is respiration considered as exothermic process?
Ans :
Respiration is an exothermic process because energy is given out in respiration.
TWO MARKS QUESTIONS
36. Write the essential condition for the following reaction to take place:
2AgBr $ 2Ag + Br2
Write application of this reaction.
Ans :
The reaction will take place in presence of sunlight.
This reaction is used in black and white photography.
37. (a) Complete the following equation for the chemical
reaction:
FeSO4(s) Heat Fe2O3 + ___ +___
(b) What happens when water is added to quicklime
(CaO)? Write the chemical equation.
Ans :
(a) 2FeSO4(s) Heat Fe2O3(s) + SO2(g) + SO3(g)
(b) Slaked lime Ca(OH)2 is formed. Hissing sound and lot of heat is also produced:
CaO(s) + H2O(l) $ Ca(OH)2(aq)
38. Write balanced chemical equation for the following reactions:
a. Hydrogen sulphide burns in air to give water and sulphur dioxide.
b. Barium chloride reacts in aqueous solution with zinc sulphate to give zinc chloride and barium sulphate.
Ans :
(a).
2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g)
(b)
BaCl(aq) + ZnSO(aq) $ BaSO4(s) + ZnCl2(aq)
39. List two observations that are noticed when an iron nail is put inside copper sulphate solution. Write the chemical equation for the reaction that occurs.
Ans :
The blue coloured solution will become pale green.
Reddish brown metal will get deposited.
( ) Blue
Fe s CuSO aq FeSO aq Cu s () ( ) ( ) ()
( )( ) Pale Green Reddish brown
+ + 4 4 $
40. Name the reducing agent in the following reaction:
3MnO2 + 4Al $ 3Mn + Al2O3
State which is more reactive, Mn or Al and Why?
Ans :
Al is the reducing agent. Al is more reactive than Mn.
Reason: It is because Al is displacing Mn from MnO2
.
41. “We need to balance a skeleton chemical equation”.
Give reason to justify the statement.
Ans :
We must balance a skeletal equation so as to ensure that the reaction follows ‘Law of conservation of mass’.
The total mass of reactants must be equal to the total mass of products, that is why all reactions should he
balanced.
42. A metal is treated with dilute H2
SO4. The gas evolved
is collected by the method as shown in figure.
Answer the following questions:
a. Name the gas liberated.
b. Name the method used for collection of gas.
c. Is the gas soluble or insoluble in water?
d. Is the gas lighter or heavier than air?
Ans : [CBSE 2015, CBSE 2010]
a. The gas liberated is H2.
b. It is collected by downward displacement of water.
c. The gas is insoluble in water.
d. Hydrogen gas is lighter than air.
43. Giving an example list two important information which makes a chemical equation more useful
(informative).
Ans :
a. It should include physical states of reactants and products.
b. It should specify conditions under which reaction takes place e.g.,
2Na(s) + 2H2O(l) $ 2NaOH(aq) + H2(g) (Cold)H2(g) + Cl2(g) sunlight 2HCl(g)
44. Consider the following chemical equation:
X + Barium chloride $ Y + Sodium chloride (White ppt)
Identify (a) X and Y (b) The type of reaction.
Ans :
(a) X is silver nitrate, Y is silver chloride.
2 2 AgNO aq BaCl aq AgCl Ba NO aq () () ( )( ) 3
( ) White ppt
3 2 32 + + $ .
(b) The reaction is an example of double displacement
(precipitation) reaction.
45. (a) Write a balanced chemical equation for the process of photosynthesis.
(b) When do desert plant take up carbon dioxide and perform photosynthesis.
Ans :
a. 6CO2(g) + 6H2O(l) chlorophyll sunlight C6H12O6(aq) + 6O2(g)
b. Desert plant take up carbon dioxide and perform photosynthesis at night.
46. Two reactions are given below:
a. 2KI + Cl2 $ 2KCl + I2
b. 2K + Cl2 $ 2KCl
Identify the type of reaction, giving justification in each case.
Ans :
a. Displacement reaction because Cl2 is displacing I2 from KI solution.
b. Combination reaction because K reacts with Cl2 to form potassium chloride.
47. On heating copper powder in air, the surface of copper powder becomes coated with black CuO. How can this black coating be converted into brown copper? Write
chemical equation for the reaction that occurs during the colour change.
Ans :
2Cu + O2 Heat 2CuO (Black)
Copper oxide on heating with H2 will change back to reddish brown copper metal.
CuO(s) + H2(g) Heat Cu(s) + H2
O(g)
48. What is observed when a solution of potassium iodide is added to a solution of lead nitrate? Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
Ans :
Yellow precipitate is formed due to formation of lead
iodide.
It is a precipitation as well as double displacement
reaction.
Pb( )( ) ( ) ( ) ( ) NO aq KI ag PbI s KNO aq 2 2
Yellow ppt
3 23 + + $
49. Write a balanced chemical equation for the process of
photosynthesis and the conditions of reaction giving
physical state of all substances.
Ans : [CBSE 2014)
6 6 CO g H O l ( ) () C H O aq O g ( ) () 6 chlorophy II
sunlight
2 2 6 12 6 2 + +
50. Give one example of each:
a. Chemical reaction showing evolution of a gas.
b. Change in colour of a substance during chemical
reaction.
Ans : [CBSE 2013]
a. 2K(s) + 2H2
O(l) $ 2KOH(aq) + H2
(g)
b. FeSO4
.7H2
O(aq) Heat FeSO4
(s) + 7H2
O(l)
(Pale green) (Dirty white)
51. Translate the following statement into chemical
equation and then balance it. “A metal in the form of
ribbon burns with a dazzling white flame and changes
into white powder.”
Ans : [CBSE 2013]
2Mg(s) + O2
(g) Burning 2MgO(s) + Light + Heat
52. It has been found that marble of Taj is getting corroded
due to development of industrial areas around it.
Explain this fact giving a chemical equation.
Ans : [CBSE 2013]
Taj is made up of CaCO3
which reacts with acid
formed by pollution of SO2
(g) and NO2
from Mathura
refinery and other industries.
CaCO3
+ 2H2
SO4
$ CaSO4
+ CO2
+ 2H2
O
CaCO3
+ 2HNO3
$ Ca(NO3)2
+ H2
O + CO2
53. Consider the chemical equations given below and
answer the questions which follow:
(i) CuO + H2
Heat Cu + H2
O
(ii) ZnO + C Heat Zn + CO
a. Name the substances that are oxidised and
reduced respectively in each case,
b. Identify the reducing agent in each case.
Ans : [CBSE 2013]
a. H2
is getting oxidised to H2
O, CuO getting reduced
to Cu.
b. H2
is reducing agent in (i) reaction whereas C is
reducing agent in second reaction.
54. What is a redox reaction? Identify the substances
oxidised and the substance reduced in the following
reactions:
a. MnO2
+ 4HCl $ MnCl2
+ Cl2
+ H2
O
b. CuO + H2 $ Cu + H2
O
Ans : [CBSE 2012]
Redox reaction is a reaction in which oxidation and
reduction takes place simultaneously.
c. HCl is the substance oxidised, MnO2
is the
substance getting reduced.
d. H2
is getting oxidised, CuO is getting reduced.
55. Write balanced chemical equations for the following
reactions:
a. Silver bromide on exposure to sunlight decomposes
into silver and bromine.
b. Sodium metal reacts with water to form sodium
hydroxide and hydrogen gas.
Ans : [CBSE 2012]
a. 2AgBr(s) sunlight 2Ag(s)+ Br2
(g)
b. 2Na(s) + 2H2
O(l) $ 2NaOH(l) + H2(g)
56. Identify the type of reaction from the following
equations:
a. CH4
+ 2O2 $ CO2
+ 2H2
O
b. Pb(NO3
)2
+ 2KI $ PbI2
+ 2KNO3
c. CaO + H2
O $ Ca(OH)2
d. CuSO4
+ Zn $ ZnSO4
+ Cu
Ans : [CBSE 2012]
a. Oxidation reaction
b. Double displacement reaction
c. Combination reaction
d. Displacement reaction
57. Write balanced equation for the reaction between Mg
and hydrochloric acid. Name the product obtained,
identify the type of reaction.
Ans : [CBSE 20i2]
Mg(s) + 2HCl(dil) $ MgCl2
(aq) + H2
(g)
Magnesium chloride and hydrogen gas are formed in
this reaction. It is a displacement reaction.
58. a. What is colour of ferrous sulphate crystals? How
does this colour change after heating?
b. Name the products formed on strongly heating
ferrous sulphate crystals. What type of chemical
reaction occurs in this change?
Ans : [CBSE 2012.2009]
a. FeSO H O 4 2 $ 7 crystals are pale green in colour.
They become dirty white on heating.
b. Ferric oxide, sulphur dioxide and sulphur trioxide
are formed:
2FeSO4
(s) Heat Fe2
O3
(s) + SO2
(g) + SO3
(g)
It is a decomposition reaction.
59. Reaction of compound X with aluminium is used to
join railway tracks or cracked machine parts.
a. Identify the compound.
b. Name the reaction.
c. Write a balanced chemical equation for the
reaction.
Ans : [CBSE 2012]
a. The compound X is Fe2
O3
(Ferric oxide) or Iron
(III) oxide.
b. It is called Thermite Reaction.
c. 2Al(s) + Fe2
O3
(s) Heat Al2
O3
(s) + 2Fe(l)
60. Using balanced chemical equation explain the
difference between a displacement reaction and a
double displacement reaction.
Ans : [CBSE 2012, 2011]
Displacement reaction: A reaction in which a more
reactive element displaces a less reactive element from
its salt solution e.g.,
2KBr(aq) + Cl2
(g) $ 2KCl(aq) + Br2
(aq)
Double displacement reaction: A reaction in which
two compounds exchange their ions to form two new
compounds e.g.,
KOH + HNO3
$ KNO3
+ H2
O
61. Give an example each for thermal decomposition
and photochemical decomposition reactions. Write
balanced chemical equation also.
Ans : [CBSE 2012]
Thermal decomposition:
ZnCO3
(s) Heat ZnO(s) + CO2
(g)
Photochemical decomposition:
2AgI(s) sunlight 2Ag(s) + I2
(g)
62. Why are decomposition reactions called the opposite
of combination reactions? Give chemical equations for
these reactions.
Ans : [CBSE 2012]
In decomposition reactions, a compound is broken
down into one or more elements or compounds e.g.,
CaCO3
(s) Heat CaO(s) + CO2
(g)
In combination reactions, two or more elements
or compounds combine to form a new compound.
Therefore, decomposition reactions are opposite to
combination reactions e.g.,
3Mg(s) + N2
(g) Burns Mg3
N2
(s)
63. Why does the colour of copper sulphate solution
changes when an iron pin is dipped in it?
Ans : [CBSE 2012]
Iron being more reactive displaces copper from copper
sulphate (Blue) solution to form iron (II) sulphate
(Pale green) solution and reddish brown copper metal
gets deposited.
Fe(s) + CuSO4
$ FeSO4
(aq) + Cu(s)
64. Translate the following statements into chemical
equations and then balance them:
a. Hydrogen gas combines with nitrogen to form
ammonia.
b. Hydrogen sulphide gas burns in air to give water
and sulphur dioxide.
c. Barium chloride reacts with aluminium sulphate
to give aluminium chloride and a precipitate of
barium sulphate. State the two types in which
this reaction can be classified.
d. Potassium reacts with water to give potassium
hydroxide and hydrogen gas.
Ans : [CBSE 2012]
a. 3H2
(g) + N2
(g) $ 2NH3
(g)
b. 2H2
S(g) + 3O2(g) $ 2H2
O(l) + 2SO2
(g)
c. 3 3 BaCl aq Al SO aq BaSO s AlCl aq 2 24 ( ) ( )( ) + + 3 $ 4 3 () ( ) 2
This reaction can be classified as a double
displacement reaction as the two reacting species
(BaSO4
, Al2
SO4
)3
undergoes mutual exchange
of ions. It can also be classified as precipitation
reaction, since a white ppt. of BaSO4
is obtained.
d. 2K(s) + 2H2
O(l) $ 2KOH(aq) + H2
(g)
65. When a metal X is added to salt solution of metal Y,
the following chemical reaction takes place:
Metal X + Salt solution of Y $
Salt solution of X + Metal Y
Mention the inference you draw regarding the
reactivity of metal X and Y and also the type of
reaction. State the reason of your conclusions.
Ans : [CBSE 2012]
X is more reactive than Y because , X displaces Y from
its salt solution. Hence, this reaction is an example of
displacement reaction.
66. Identify the type of each of the following reactions:
a. A reaction in which a single product is formed
from two or more reactants.
b. The reaction mixture becomes warm.
c. An insoluble substance is formed.
d. External surface of the container in which reaction
takes place becomes cold.
Ans : [CBSE 2012]
a. Combination reaction
b. Exothermic reaction
c. Precipitation reaction (Double displacement
reaction)
d. Endothermic reaction
67. A solution of potassium chloride when mixed with
silver nitrate solution, an insoluble white substance is
formed. Write the chemical reaction involved and also
mention the type of reaction.
Ans : [CBSE 2012, 2011, 2010]
AgNO3
(aq) + KCl(aq) $ AgCl(s)+KNO3
(aq) (White ppt.)
It is a double displacement reaction.
68. Using a suitable chemical equation justify that some
chemical reactions are determined by
a. Change in colour.
b. Change in temperature.
Ans : [CBSE 2011]
a. Change in colour: Blue coloured crystalline
copper sulphate crystals changes to white CuSO4
(anhydrous) on heating.
CuSO4
.5H2
O Heat CuSO4
+ 5H2
O
(Blue) (Dirty white)
b. Change in temperature:
CaO(s) + H2
O(l) $ Ca(OH)2
(aq) + Heat
69. (a) A solution of substance X is used for white
washing. What is substance X? Write the chemical
reaction of X with water.
(b) Why does the colour of copper sulphate solution
changes when iron nail is dipped in it?
Ans : [CBSE 2011]
a. X is CaO, calcium oxide
CaO(s) + H2
O(l) $ Ca(OH)2
(aq)
b. It is because Fe displaces Cu from CuSO4
(blue)
solution to form FeSO4
(pale green) and reddish
brown Cu metal gets deposited.
70. Balance the following reactions:
a. BaCl2
+ H2
SO4
$ BaSO4
+ HCl
b. Ca(OH)2
+ HNO3
$ Ca(NO3
)2
+ H2
O
c. Pb(NO3
)2
$ PbO + NO2
+ O2
d. MnO2
+ HCl $ MnCl2
+ Cl2
+ H2
O
Ans : [CBSE 2011, 2009, 2008, 2008C]
a. BaCl aq H SO dil BaSO s HCl aq 2 24 ( ) ( ) () ( ) + + $ 4 2
b. Ca OH aq HNO Ca NO aq H O l ( )( ) 233 + + 2 2 $ ( ) ( ) () 2 2
c. 2 24 Pb NO s PbO s NO g O g ( )() () () () Heat
32 2 2 + +
d. MnO HCl MnCl Cl H O 2 2 + + 4 2 $ 2 + 2
71. Write the balanced equation for the following reactions
and identify the type of reaction in each case:
a. Potassium bromide + Barium iodide $
Barium bromide + Potassium Iodide
b. Hydrogen(g) + Chlorine(g) $ Hydrogen
chloride(g)
Ans : [CBSE 2011]
a. 2KBr(aq) + BaI2 $ BaBr2
(aq) + 2KI(aq)
It is double displacement reaction.
b. H2
(g) +. Cl2
(g) sunlight 2HCl(g)
It is combination reaction.
72. A zinc plate was put into solution of copper sulphate
kept in a glass container. It was found that blue colour
of the solution gets fader and fader with passage of
time. After few days when zinc plate was taken out of
the solution, a number of holes were observed on it.
a. State the reason for the changes observed on zinc
plate.
b. Write the chemical equation for the reaction
involved.
Ans : [CBSE 2011]
a. Zinc displaces copper from copper sulphate
solution to form colourless ZnSO4 and copper
metal is deposited. Zinc gets consumed due to
which holes are formed.
b. Zn(s) + CuSO4
(aq) $ ZnSO4
(aq) + Cu(s)
73. A white salt on heating decomposes to give brown
fumes and a white residue is left behind.
a. Name the salt.
b. Write the equation for the decomposition reaction.
Ans : [CBSE 2011]
a. Lead nitrate
b. 2 24 Pb NO s PbO s NO g O g ( )() () () ()
( ) White ( ) ( )
Heat
Residue Brown
3 3 + + 2 2
74. When a solution of potassium iodide is added to a
solution of lead nitrate in a test tube, a reaction takes
place.
a. What type of reaction is this?
b. Write the balanced chemical equation to represent
the above reaction.
Ans : [CBSE 2011, 2010, 2008]
a. It is precipitation as well as double displacement
reaction.
b. Pb NO aq KI aq Pbl s KNO aq ( )( ) ( ) ( ) ( ) 3 2 + + 2 2 $ 3
75. Define combination reaction. Give one example of a
combination reaction which is also exothermic.
Ans : [CBSE 2011]
Combination reaction: The reaction in which two
or more elements or compounds combine to form
compound(s) e.g.,
C(s) + O2
(g) $ CO2
(g) + Heat
It is an exothermic, combination reaction.
76. What happens when an aqueous solution of sodium
sulphate reacts with an aqueous solution of barium
chloride? State the physical conditions of reactants in
which the reaction between them will not take place.
Write the balanced chemical equation for the reaction
and name the type of reaction.
Ans : [CBSE 2016, 2010]
White precipitate of BaSO4
is formed.
BaCl2 24 4 ( ) ( ) () ( ) aq Na SO aq BaSO s NaCl aq + + $ 2
It is a double displacement reaction. If reactants are
taken in solid state, products will not be formed.
77. What is redox reaction? When a magnesium ribbon
burns in air with a dazzling flame and forms a white
ash, is magnesium oxidised or reduced. Why?
Ans : [CBSE 2010, 2009]
Redox reaction is a reaction in which oxidation and
reduction takes place simultaneously.
Mg is getting oxidised because it is gaining oxygen
to form magnesium oxide.
78. Write any two observations in an activity which may
suggest that a chemical reaction has taken place. Give
an example in support of your answer.
Ans : [CBSE 2010]
a. Change in colour:
AgNO ( ) ( ) () ( ) aq KI aq AgI s KNO aq
( ) Yellow ppt
3 3 + + $
b. Evolution of gas:
Zn(s) + H2
SO4
(aq) $ ZnSO4
(aq) + H2
(g)
79. When the powder of common metal is heated in open
china dish its colour turns black. However, when
hydrogen is passed over the hot black substance so
formed, it regains its original colour. Based on the above information answer the following questions:
a. What type of chemical reaction takes place in
each of the two given steps?
b. Name the metal initially taken in powdered form.
Write balanced equations for both the reactions.
Ans : [CBSE 2010]
a. Oxidation reaction, Redox reaction
b. Copper metal was present initially
2Cu() () s O g CuO s( )
( )
Heat
Black
+ 2
CuO s H g () () Cu s H O l () () Heat + + 2 2
( ) Reddish brown
80. Why do we store silver chloride in dark coloured
bottle? Explain in brief.
Ans : [CBSE 2010]
It is done so as to cut off the exposure to sunlight.
AgCl is photosensitive, it will decompose to Ag and
Cl2
in the presence of sunlight.
2AgCl(s) sunlight 2Ag(s) + Cl2
( g)
81. “Oxidation and reduction processes occur
simultaneously”. Justify this statement with the help
of example.
Ans : [CBSE 2010]
Oxidation involves loss of electrons or addition of
oxygen. Whereas reduction involves gam of electrons
or addition of hydrogen e.g.,
H2
is getting oxidised to H2
O, CuO is getting reduced
to Cu.
It shows oxidation and reduction occur simultaneously.
82. When magnesium ribbon bums in air or oxygen, a
product is formed. State the type of chemical reaction
and name the product formed in the reaction. Write
balanced chemical equation for the reaction.
Ans : [CBSE 2009(C)]
It is a combination reaction. The product formed is
magnesium oxide:
2Mg(s) + O2
(g) $ 2MgO(s)
83. Distinguish between a displacement reaction
and a double displacement reaction. Identify the
displacement and the double displacement reaction
from the following reactions:
a. HCl(aq) + NaOH(aq) $ NaCl(aq) + H2
O(l)
b. Fe(s) + CuSO4
(aq) $ FeSO4
(aq) + Cu(s)
Ans : [CBSE 2009]
Displacement Reaction: When a more reactive metal
displaces a less reactive metal from its salt solution.
Double displacement reaction: When two compounds
exchange their ions to form two new compounds.
a. Double displacement reaction.
b. Displacement reaction.
84. What is an oxidation reaction? Give an example of
oxidation reaction. Is oxidation an exothermic or an
endothermic reaction?
Ans : [CBSE 2009]
Oxidation reaction: The reaction in which O2
is added
or H2
is removed or loss of electrons takes place is
called oxidation reaction. E.g.,
2Cu(s) + O2
(g) $ 2CuO(s)
It is an exothermic reaction.
THREE MARKS QUESTIONS
85. Decomposition reactions require energy either in the
form of heat, light or electricity for breaking down the
reactants. Write an equation each for decomposition
reactions where energy is supplied in the form of heat,
light and electricity.
Ans : [CBSE 2018, 2014]
a. CaCO3
(s) Heat CaO(s) + CO2
(g)
b. 2AgBr(s) sunlight 2Ag(s) + Br2
(g)
c. 2H2
O(l) Electricity 2H2
(g) + O2
(g)
86. In the electrolysis of water:
a. Name the gas collected at the cathode and anode
respectively.
b. Why is volume of gas collected at one electrode
double than that at the other? Name this gas.
c. How will you test this gas?
Ans : [CBSE 2012, CBSE Sample Paper 2018]
a. Hydrogen is collected at the cathode, oxygen is
collected at the anode.
b. It is because H2
O contains hydrogen and oxygen
in the ratio 2 : 1.
c. Bring a burning matchstick near the gas, if the
gas burns with ‘pop’ sound, the gas is H2
.
87. Define the term decomposition reaction. Give
one example each of thermal decomposition and
electrolytic decomposition reactions.
Ans : [CBSE 2016]
Decomposition reaction: The reaction in which a
compound is broken down into simpler elements or
compounds:
a. CaCO3
(s) Heat CaO(s) + CO2
(g)
b. 2H2
O(l) Electricity 2H2
(g) + O2
(g)
88. Name two salts that are used in black and white
photography. Give equations for the reactions when
these are exposed to sunlight.
Ans : [CBSE 2016]
AgBr (Silver bromide) and AgI (Silver iodide) are
used in black and white photography.
2AgBr(s) sunlight 2Ag(s) + Br2
(g)
2AgI(s) sunlight 2Ag(s) + I2
(g)
89. State one example each characterised by following
along with suitable chemical equation.
a. Change in state,
b. Evolution of gas,
c. Change in temperature.
Ans : [CBSE 2016]
a. Change in state:
AgNO3
(aq) + HCl(aq) $ AgCl(s) + HNO3
(aq)
b. Evolution of gas:
CaCO s HCl dil CaCl aq H O CO g 3 2 ^ ^ ^ ^^ h h hhh + + $ 2 2 l + 2
c. Change in temperature:
d. CH4
(g) + 2O2
(g) $ CO2
(g) + 2H2
O(l) + Heat
90. Name the type of reactions represented by the
following equations:
a. CaO + H2
O $ Ca(OH)2
b. 3BaCl2
+ Al2
(SO4
) $ 3BaSO4
+ 2AlCl3
c. 2FeSO4
Heat Fe2
O3
+ SO2
+ SO3
Ans : [CBSE 2015]
a. Combination reaction,
b. Double displacement reaction,
c. Decomposition reaction.
91. Write the chemical equation of the reaction in which
the following changes take place with an example of
each.
a. Change in colour,
b. Change in tem-perature,
c. Formation of precipitate.
Ans : [CBSE 2015]
a. Change in colour:
Zn s FeSO aq ZnSO aq Fe s () ( ) ( ) ()
( ) Colourless
+ +
Pale green
4 4 $
b. Change in Temperature:
2Mg + O2
(g) $ 2MgO(s) + Heat
c. Formation of precipitate:
Pb NO aq HCl dil Pbcl s HNO aq ( )( ) ( ) () ( ) 2 2
White ppt
32 2 3 + + $
92. State the type of chemical reactions and chemical
equations that take place in the following:
a. Magnesium wire is burnt in air.
b. Electric current is passed through water.
c. Ammonia and hydrogen chloride gases are mixed.
Ans : [CBSE 2015]
a. 2Mg(s) + O2
(g) $ 2MgO(s);
b. Oxidation reaction
c. 2H2
O(l) $ 2H2
(g) + O2
(g);
Decomposition reaction
d. NH3
(g) + HCl(g) $ NH4
Cl(s);
Combination reaction
93. Write the balanced chemical equations for the
following chemical reactions:
a. Hydrogen + Chlorine $ Hydrogen Chloride
b. Lead + Copper Chloride $ Lead chloride +
Copper
c. Zinc oxide + Carbon $ Zinc + Carbon
Monoxide
Ans : [CBSE 2013]
a. H2
(g) + Cl2
(g) $ 2HCl(g)
b. Pb(s) + CuCl2
(aq) $ PbCl2
(s) + Cu(s)
c. ZnO(s) + C(s) $ Zn(s) + CO(g)
94. Write chemical equations for the reactions taking
place when
a. Iron reacts with steam
b. Magnesium reacts with dil. HCl
c. Copper is heated in air
Ans : [CBSE 2014]
a. 3Fe(s) + 4H2
O(g) $ Fe3
O4
(s) + 4H2
(g)
b. Mg(s) + 2HCl(dil) $ MgCl2
(aq)
c. 2Cu(s) + O2
(g) $ 2CuO(s)
95. In a schematic diagram for the preparation of hydrogen
gas as shown in the figure. What would happen if the
following changes are made
a. In place of zinc granules, same amount of zinc
dust is taken in the test tube?
b. Instead of dilute sulphuric, dilute hydrochloric
acid is taken?
c. Sodium hydroxide is taken in place of dilute
sulphuric acid and the flask is heated?
Ans : [CBSE 2014, 2010]
a. Zinc dust will react faster, H2
(g) will be liberated
at a faster rate.
b. Same volume of H2
(g) will be formed.
c. On heating Zn with NaOH, hydrogen gas will be
formed at a faster rate.
96. (a) Why is it necessary to balance a chemical
equation?
(b) Write the balanced chemical equation for the
following reactions:
(i) Natural gas burns in air to form carbon
dioxide and water.
(ii) During respiration, glucose combines with
oxygen and forms carbon dioxide and water
along with the release of energy.
Ans : [CBSE 2013]
a. Chemical equation must be balanced so as to
follow the law of conservation of mass.
b. (i) CH4
(g) + 2O2(g) $ CO2
(g) + 2H2
O(l)
(ii) C H O s O g CO g H O l Heat 6 12 6 2 () ( ) ( ) () + ++ 6 66 $ 2 2
97. (i) Solid calcium oxide was taken in a container and
water was added slowly to it.
(a) Write the observations.
(b) Write the chemical formula of the product
formed.
(ii) What happens when carbon dioxide is bubbled
through lime water (a) in small amount (b) in
excess?
Ans : [CBSE 2013, 2012, 2010]
(i) (a) The container becomes hot and hissing sound
is produced.
(b) Ca(OH)2
is the formula of the product formed.
(ii) (a) Lime water turn milky when CO2
(g) is passed
through it:
Ca(OH)2
(aq) + CO2
(g) $ CaCO3
(s) + H2
O(l)
(b) If excess of CO2
is passed milkiness disappears:
CaCO3
(s) + CO2
(g) + H2
O(s) $ Ca(HCO3
)2
(aq)
98. Write the balanced chemical equation for the following
reaction and identify the type of reaction.
Thermite reaction, iron (III) oxide reacts with
aluminium and give molten iron and aluminium oxide.
Ans : [CBSE 2012]
Fe2
O3
(s) + 2Al(s) $ Al2
O3
(s) + 2Fe(l)
It is displacement as well as redox reaction.
99. An aqueous solution of metal nitrate ‘P’ reacts with
sodium bromide solution to form yellow precipitate
‘Q’ which is used in photography. ‘Q’ on exposure
to sunlight undergoes decomposition to form metal
present along with a reddish brown gas. Identify ‘P’
and ‘Q’ write the balanced chemical equation for the
chemical reaction. List the two categories in which
reaction can be placed.
Ans : [CBSE 2012]
‘P’ is silver nitrate (AgNO3
)
AgNO3
(aq) + NaBr(ag) $ AgBr(s) + NaNO3
(aq)
(P) (Yellow ppt)
This reaction is categorised as double displacement as
well as precipitation reaction.
2AgBr(s) sunlight 2Ag(s) + Br2
(g)
The above reaction is photochemical decomposition
reaction.
100. A green coloured hydrated metallic salt on heating
loses water of crystallisation molecules and gives a gas
with suffocating smell. Identify the salt and write the
chemical equation for the reaction.
Ans : [CBSE 2011]
The salt is FeSO H O 4 2 $ 7 (Hydrated ferrous sulphate)
FeSO 7 7 H O FeSO s H O l () () Heat
42 4 2 $ +
2FeSO s Fe O s SO g SO g ( ) () () () Heat
4 23 2 3 + +
101. a. Can combination reaction be an oxidation
reaction?
b. How will you test whether the gas evolved in a
reaction is hydrogen?
c. Why does copper not evolve hydrogen on reacting
with dilute sulphuric acid?
Ans : [CBSE 2011]
a. Yes, combination reaction can be called a
oxidation reaction.
b. Bring a burning splinter near the gas, if it burns
with pop sound, it is hydrogen gas.
c. It is because copper is less reactive than hydrogen.
102. Write balanced equations for the following reactions:
a. Aluminium + Bromine $ Aluminium bromide
b. Calcium carbonate Heat
Calcium oxide + Carbon dioxide
c. Silver chloride sunlight Silver + Chlorine
Ans : [CBSE 2011]
a. 2Al(s) + 3Br2
(g) $ 2AlBr3
(s)
b. CaCO3
(s) Heat CaO(s) + CO2
(g)
c. 2AgCl(s) sunlight 2Ag(s) + Cl2
(g)
103. a. Why is respiration considered an exothermic
reaction?
b. Define the terms oxidation and reduction,
c. Identify the substance that is oxidised and reduced
in the following reaction:
CuO(s) + Zn(s) heat Cu(s) + ZnO(s)
Ans : [CBSE 2011]
a. In respiration, energy is released, therefore, it is
considered an exothermic reaction.
b. Oxidation involves addition of O2
or loss of
electrons. Reduction involves addition of H2
or
gain of electrons.
c. Zn is getting oxidised, CuO is getting reduced.
104. Write balanced chemical equations for the following
reactions:
a. Hydrogen sulphide gas burns in air to give water
and sulphur dioxide.
b. Barium chloride reacts with zinc sulphate to give
zinc chloride and barium sulphate.
c. Natural gas bums in air to form carbon dioxide
and water.
Ans : [CBSE 2011]
a. 2H2
S(g) + 3O2
(g) $ 2H2
O(l) + 2SO2
(g)
b. BaCl aq ZnSO aq BaSO s ZnCl aq 2 4 42 ( ) ( ) () ( ) + + $ c. CH4
(g) + 2O2
$ CO2
(g) + 2H2
O(l)
FIVE MARKS QUESTIONS
105. Write balanced chemical equation for the following
statements:
a. NaOH solution is heated with zinc granules.
b. Excess of carbon dioxide is passed through lime
water.
c. Dilute sulphuric acid is added to sodium carbonate.
d. Egg shell is dropped in hydrochloric acid,
e. Copper (II) oxide reacts with dilute hydrochloric
acid.
Ans : [CBSE 2016]
a. Zn(s) + 2NaOH $ Na2
ZnO2
+ H2
b. Ca(OH)2
+ 2CO2 $ Ca(HCO3
)2
c. Na2
CO3
+ H2
SO4 $ Na2
SO4
+ H2
O + CO2
d. CaCO3
(s) + 2HCl(dil) $ CaCl2
+ H2
O + CO2
e. CuO(s) + 2HC1 $ CuCl2
+ H2
O
106. Identify the type of chemical reaction in the following
statement and define each of them:
a. Digestion of food in our body.
b. Rusting of iron.
c. Heating of manganese dioxide with aluminium
powder.
d. Blue colour of copper sulphate solution disappears
when iron filings are added to it.
e. Dilute hydrochloric acid is added to sodium
hydroxide solution to form sodium chloride and
water.
Ans : [CBSE 2016]
a. Decomposition reaction: It is a process in which a
compound is broken down into simple substances.
b. Oxidation: The process in which oxygen is added
or electrons are lost.
c. Displacement reaction: The reaction in which a
more reactive element can displace a less reactive
element from its salt solution. Oxidation and
Reduction are taking place simultaneously in
rusting of iron.
d. Displacement reaction: The reaction in which a
more reactive element can displace a less reactive
element.
e. Neutralisation reaction: The reaction in which
acid reacts with base to form salt and water.
107. Define chemical reaction. State four observations
which helps to determine whether a chemical reaction
has taken place or not. Write one example of each
observation with a balanced chemical equation.
Ans : [CBSE 2015]
Chemical reaction is a reaction which represents a
chemical change.
a. Change in colour:
Cu s AgNO aq Cu NO aq Ag s ( ) ( ) ( )( ) ( ) 2 2
( ) Colourless ( ) Blue
+ + 3 3 $
b. Evolution of gas:
CaCO ( )s CaO s CO g () ()
( )
Heat
Carbon dioxide gas
3 2 +
c. Formation of precipitate:
Pb( )( ) NO aq KI PbI s KNO aq 2 2 () ( )
( ) Yellow ppt
32 2 3 + + $
d. Change in temperature:
CaO(s) + H2
O(l) $ Ca(OH)2
+ Heat
108. a. Define a balanced chemical equation. Why should
an equation be balanced?
b. Write a balanced chemical equation for the
following reactions:
(i) Phosphorus burns in the presence of chlorine
to form phosphorus pentachloride.
(ii) Burning of natural gas.
(iii) The process of respiration.
Ans : [CBSE 2015]
a. Balanced chemical equation is a equation in which
number of atoms of various elements are equal on
both sides of the equation.
The equation should be balanced due to law of
conservation of mass.
b. (i) 2P(s) + 5Cl2
(g) $ 2PCl5
(S)
(ii) CH4
(g) + O2
(g) $ CO2
(g) + 2H2
O(l)
(iii) C6
H12O6
(s) + 6O2
(g) $ 6CO2
(g) + 6H2
O(l)
109. (a) Write one example for each of decomposition
reaction carried out with the help of (i) Electricity,
(ii) Heat, (iii) Light.
(b) Which of the following statement is correct and
why?
Copper can displace silver from silver nitrate
solution and silver can displace copper from
copper sulphate solution.
Ans : [CBSE 2014]
a. (i) CaCO3
(s) Heat CaO(s) + CO2
(g)
(ii) 2AgBr(s) sunlight 2Ag(s) + Br2
(g)
(iii) 2H2
O(l) Electricity 2H2
(g) + O2
(g)
b. Copper can displace Ag from AgNO3
(aq) solution
because Cu is more reactive than Ag.
Cu s AgNO aq Cu NO aq Ag s () ( ) ( )( ) () + + 2 2 3 3 $ 2
110. Identify the type of reactions taking place in each of
the following:
a. Barium chloride solution is mixed with copper
sulphate solution and white precipitate is formed.
b. On heating copper powder in china dish, the
surface of copper powder turns black.
c. On heating green coloured ferrous sulphate
crystals, raddish brown solid is left and smell
of a gas having odour of burning sulphur is
experienced.
d. Iron nails when left dipped in blue copper sulphate
solution become reddish brown in colour and the
blue colour of copper sulphate fades away.
e. Quick lime reacts vigorously with water releasing
a large amount of heat.
Ans : [CBSE Sample Paper 2009]
a. Double displacement reaction,
b. Oxidation,
c. Decomposition reaction,
d. Displacement reaction,
e. Combination reaction.
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