Chap 1 : Chemical Reactions and Equations www.cbse.

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CHAPTER 1
Chemical Reactions and Equations

ONE MARK QUESTIONS following reaction:

Sodium hydroxide + Sulphuric acid $
Ans : [CBSE 2013]
1. In electrolysis of water, why is the volume of gas
collected over one electrode double that of gas 2NaOH + H2SO4 $ Na2SO4 + 2H2O
collected over the other electrode. 9. Name and state the law which is kept in mind when
Ans : [CBSE S.R 2018, CBSE 2009, 2012, 2013] we balance chemical equations.
Water contains hydrogen and oxygen in the ratio of Ans : [CBSE 2012]
2 : 1, that is why volume of H2 is double than that of Law of conservation of mass. It states Matter can
oxygen. neither be created nor be destroyed. The total mass
2. What can be seen when a strip of copper metal is of reactants must be equal to total mass of products.
placed in a solution of silver nitrate? 10. What is meant by a chemical reaction?
Ans : [CBSE 2015] Ans : [CBSE 2011]
The solution will become blue, shiny silver metal will Chemical reaction, a process in which one or more
get deposited. substances, the reactants, are converted to one or more
Cu(s) + 2AgNO3(aq) $ Cu(NO3)2 (aq) + 2Ag(s) different substances, the products. Substances are
either chemical elements or compounds. A chemical
3. State one industrial application of reduction process.
reaction rearranges the constituent atoms of the
Ans : [CBSE 2015] reactants to create different substances as products
It is used in the extraction of metals e.g.,
Heat 11. AgNO3(aq) + NaCl(aq) $ AgCl . + NaNO3(aq)
ZnO(s) + C(s) Zn(s) + CO2(g)
FeS + H2SO4 $ FeSO4 + H2S -
4. Which one of the following is a chemical change? Give Consider the above mentioned two chemical equations
reason also. with two different kinds of arrows (- and . ) along
(a) Burning of wax (b) Melting of wax with the product. What do these two different arrows
Ans : [CBSE 2014] indicate?
Ans : [CBSE 2011]
Burning of gas is a chemical change because new
products with new properties will be formed on - shows evolution of gas, . represents a precipitate.
burning.
12. Hydrogen being a highly inflammable gas and
5. Which one is a chemical change: oxygen being a supporter of combustion, yet water, a
Rusting of iron or melting of iron? compound made up of hydrogen and oxygen is used to
Ans : [CBSE 2014] extinguish fire. Why?
Ans : [CBSE 2011]
Rusting of iron is a chemical change.
H2O is a compound constituted of hydrogen of oxygen
6. State one basic difference between a physical change elements and being a compound it has different
and a chemical change. properties as compared to its constituting elements.
Ans : [CBSE 2014, 2011]
13. N2(g) + 3H2(g) $ 2NH3(g), name the type of
In a physical change, no new substance is formed. reaction.
In a chemical change, new substance(s) with new
Ans : [CBSE 2011]
properties is/are formed.
Combination reaction.
7. Name the oxidising and reducing agent in the following
reaction: 14. If copper metal is heated over a flame it develops
a coating. What is the colour and composition of
CuO + H2 $ Cu + H2O
coating?
Ans : [CBSE 2013]
Ans : [CBSE 2011]
CuO is oxidising agent H2 is reducing agent.
Black coloured coating is formed. It is a due to
8. Write a complete balanced chemical equation for the formation of copper oxide.
15. Write a balanced chemical equation to represent It is photochemical decomposition reaction.
the following reaction: carbon monoxide reacts with
hydrogen gas at 340 atm to form methyl alcohol. 25. Write a balanced chemical equation for the reaction
between sodium chloride and silver nitrate indicating
Ans : [CBSE 2011]
the physical state of the reactants and the products.
340 atm
CO(g) + 2H2(g) CH3OH(l) Ans : [CBSE 2010]
Heat
16. Which one is a chemical change: fermentation of fruit AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq)
(Silver Nitrate)
juice or diluting fruit juice? (Sodium Chloride) (Silver Chloride) (Sodium NItrate)

Ans : [CBSE 2011] 26. Complete and balance the following equation:
Fermentation of fruit juice is a chemical change. Fe2O3 + Al $
Ans : [CBSE 2010]
17. Is burning of a candle wax a physical or a chemical
change? Fe2O3 + 2Al $ 2Fe + Al2O3
Ans : [CBSE 2011] 27. Balance the following chemical equation:
Burning of a candle wax is a chemical change. Pb(NO3)2 $ PbO + NO2 + O2
Ans : [CBSE 2009]
18. Write a balanced equation for the chemical reaction
that can be characterised as precipitation reaction. 2Pb(NO3)2 Heat 2PbO + 4NO2 + O2
Ans : [CBSE 2011] 28. Identity the type of reaction in the following example:
AgNO3(aq) + NaCl(aq) $ AgCl(s) + NaNO3(aq) Na2SO4(aq) + BaCl2(aq) $ BaSO4(s) + 2NaCl(ag)
It is a precipitation reaction. Ans : [CBSE 2008(C)]
19. State the main difference between endothermic Double displacement reaction.
reaction and an exothermic reaction.
29. Identify the type of reaction in the following example:
Ans : [CBSE 2011] Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s)
In endothermic reaction, heat is absorbed. In Ans : [CBSE 2008(C)]
exothermic reaction, heat is evolved.
Displacement reaction.
20. What happens chemically when quick lime is added to
30. Identify the type of reaction in the following example:
water filled in a bucket?
2H2(g) + O2(g) $ 2H2O(l)
Ans : [CBSE 2010, 2008]
Ans : [CBSE 2008(C)]
Calcium hydroxide (Slaked lime) is formed with
Combination reaction.
evolution of heat and hissing sound.
CaO(s) + H2O(l) $ Ca(OH)2(aq) 31. Balance the given chemical equation:
Al(s) + CuCl2(aq) $ AlCl3(aq) + Cu(s)
21. Define oxidation and reduction.
Ans : [CBSE 2008(C)]
Ans : [CBSE 2011, 2010]
2Al(s) + 3CuCl2(aq) $ 2AlCl3(aq) + 3Cu(s)
Oxidation is a process in which oxygen is added or
loss of electrons take place. Reduction is a process in 32. Balance the given chemical equation:
which hydrogen is added or gain of electrons takes FeSO4(s)
Heat
Fe2O3(s) + SO2(g) + SO3(g)
place.
Ans : [CBSE 2008]
22. Give an example of double displacement reaction 2FeSO4(s)
Heat
Fe2O3(s) + SO2(g) + SO3(g)
(only with complete balanced equation).
Ans : [CBSE 2011, 2010] 33. Balance the following chemical equation:
Fe(s) + H2O(g) $ Fe3O4(s) + H2(g)
BaCl2(aq) + H2SO4(dil.) $ BaSO4(s) + 2HCl(aq)
It is a double displacement reaction. Ans :
3Fe(s) + 4H2O(g) $ Fe3O4(s) + 4H2(g)
23. On what basis is a chemical reaction balanced?
Ans : [CBSE 2010, 2008] 34. On adding dilute hydrochloric acid to copper oxide
powder, the solution formed is blue green. Predict the
Chemical equation is balanced on the basis of law of
new compound formed which imparts a blue green
conservation of mass.
colour to the solution.
24. What change in colour is observed when white silver Ans : [CBSE 2008]
chloride is left exposed to sun¬light? State the type of CuO + 2HCl $ CuCl2 + 2H2O
chemical reaction in this change. Copper chloride solution imparts blue green colour to
Ans : [CBSE 2010, 2009] the solution.
Grey coloured silver metal is formed and pungent
35. Why is respiration considered as exothermic process?
smelling chlorine gas is evolved.
sunlight Ans : [CBSE 2008]
2AgCl(s) 2Ag(s) + Cl2(g)
 Respiration is an exothermic process because energy is collected by the method as shown in figure.
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 : [CBSE 2016]
The reaction will take place in presence of sunlight.
This reaction is used in black and white photography.
Answer the following questions:
37. (a) Complete the following equation for the chemical a. Name the gas liberated.
reaction: b. Name the method used for collection of gas.
Heat c. Is the gas soluble or insoluble in water?
FeSO4(s) Fe2O3 + ___ +___
d. Is the gas lighter or heavier than air?
(b) What happens when water is added to quicklime
(CaO)? Write the chemical equation. Ans : [CBSE 2015, CBSE 2010]
Ans : [CBSE 2016] a. The gas liberated is H2.
Heat b. It is collected by downward displacement of water.
(a) 2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g)
c. The gas is insoluble in water.
(b) Slaked lime Ca(OH)2 is formed. Hissing sound and
d. Hydrogen gas is lighter than air.
lot of heat is also produced:
CaO(s) + H2O(l) $ Ca(OH)2(aq) 43. Giving an example list two important information
which makes a chemical equation more useful
38. Write balanced chemical equation for the following (informative).
reactions: Ans : [CBSE 2015]
a. Hydrogen sulphide burns in air to give water and
sulphur dioxide. a. It should include physical states of reactants and
b. Barium chloride reacts in aqueous solution with products.
zinc sulphate to give zinc chloride and barium b. It should specify conditions under which reaction
sulphate. takes place e.g.,
Ans : [CBSE 2016] 2Na(s) + 2H2O(l) $ 2NaOH(aq) + H2(g)
(Cold)
a. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g) sunlight
H2(g) + Cl2(g) 2HCl(g)
b. BaCl(aq) + ZnSO(aq) $ BaSO4 (s) + ZnCl2(aq)
44. Consider the following chemical equation:
39. List two observations that are noticed when an iron
X + Barium chloride $ Y + Sodium chloride
nail is put inside copper sulphate solution. Write the (White ppt)
chemical equation for the reaction that occurs. Identify (a) X and Y (b) The type of reaction.
Ans : [CBSE 2016] Ans : [CBSE 2015]
The blue coloured solution will become pale green. (a) X is silver nitrate, Y is silver chloride.
Reddish brown metal will get deposited. 2AgNO 3 (aq) + BaCl 2 (aq) $ 2AgCl . + Ba (3NO 3) 2 (aq)
Fe (s) + CuSO 4 (aq) $ FeSO 4 (aq) + Cu (s) (White ppt)

(Blue) (Pale Green) (Reddish brown) (b) The reaction is an example of double displacement
40. Name the reducing agent in the following reaction: (precipitation) reaction.
3MnO2 + 4A1 $ 3Mn + Al2O3
State which is more reactive, Mn or Al and Why? 45. (a) Write a balanced chemical equation for the process
of photosynthesis.
Ans : [CBSE 2016, 2015]
(b) When do desert plant take up carbon dioxide and
Al is the reducing agent. Al is more reactive than Mn. perform photosynthesis.
Reason: It is because Al is displacing Mn from MnO2. Ans : [CBSE 2015]
sunlight
41. “We need to balance a skeleton chemical equation”. a. 6CO2(g) + 6H2O(l) chlorophyll C6H12O6(aq) + 6O2(g)
Give reason to justify the statement. b. Desert plant take up carbon dioxide and perform
Ans : [CBSE 2015] photosynthesis at night.
We must balance a skeletal equation so as to ensure 46. Two reactions are given below:
that the reaction follows ‘Law of conservation of mass’. a. 2KI + Cl2 $ 2KCl + I2
The total mass of reactants must be equal to the total b. 2K + Cl2 $ 2KCl
mass of products, that is why all reactions should he Identify the type of reaction, giving justification in
balanced. each case.
42. A metal is treated with dilute H2SO4. The gas evolved Ans : [CBSE 2015]
 a. Displacement reaction because Cl2 is displacing I2 answer the questions which follow:
Heat
from KI solution. (i) CuO + H2 Cu + H2O
b. Combination reaction because K reacts with Cl2 (ii) ZnO + C
Heat
Zn + CO
to form potassium chloride. a. Name the substances that are oxidised and
reduced respectively in each case,
47. On heating copper powder in air, the surface of copper
b. Identify the reducing agent in each case.
powder becomes coated with black CuO. How can this
black coating be converted into brown copper? Write Ans : [CBSE 2013]
chemical equation for the reaction that occurs during a. H2 is getting oxidised to H2O, CuO getting reduced
the colour change. to Cu.
Ans : [CBSE 2015] b. H2 is reducing agent in (i) reaction whereas C is
Heat reducing agent in second reaction.
2Cu + O2 2CuO
(Black)
54. What is a redox reaction? Identify the substances
Copper oxide on heating with H2 will change back to
oxidised and the substance reduced in the following
reddish brown copper metal.
Heat reactions:
CuO(s) + H2(g) Cu(s) + H2O(g) a. MnO2+ 4HCl $ MnCl2 + Cl2 + H2O
48. What is observed when a solution of potassium iodide b. CuO + H2 $ Cu + H2O
is added to a solution of lead nitrate? Name the type Ans : [CBSE 2012]
of reaction. Write a balanced chemical equation to Redox reaction is a reaction in which oxidation and
represent the above chemical reaction. reduction takes place simultaneously.
Ans : [CBSE 2014, 2013] c. HCl is the substance oxidised, MnO2 is the
Yellow precipitate is formed due to formation of lead substance getting reduced.
iodide. d. H2 is getting oxidised, CuO is getting reduced.
It is a precipitation as well as double displacement 55. Write balanced chemical equations for the following
reaction. reactions:
Pb (NO 3) (aq) + 2KI (ag) $ PbI 2 (s) + 2KNO 3 (aq) a. Silver bromide on exposure to sunlight decomposes
Yellow ppt

49. Write a balanced chemical equation for the process of into silver and bromine.
photosynthesis and the conditions of reaction giving b. Sodium metal reacts with water to form sodium
physical state of all substances. hydroxide and hydrogen gas.
Ans : [CBSE 2014) Ans : [CBSE 2012]
sunlight
6CO 2 (g) + 6H 2 O (l)
sunlight
C 6 H 12 O 6 (aq) + 6O 2 (g) a. 2AgBr(s) 2Ag(s)+ Br2(g)
chlorophy II
b. 2Na(s) + 2H2O(l) $ 2NaOH(l) + H2(g)
50. Give one example of each:
a. Chemical reaction showing evolution of a gas. 56. Identify the type of reaction from the following
b. Change in colour of a substance during chemical equations:
reaction. a. CH4 + 2O2 $ CO2 + 2H2O
b. Pb(NO3)2 + 2KI $ PbI2 + 2KNO3
Ans : [CBSE 2013]
c. CaO + H2O $ Ca(OH)2
a. 2K(s) + 2H2O(l) $ 2KOH(aq) + H2(g) d. CuSO4 + Zn $ ZnSO4 + Cu
Heat
b. FeSO4.7H2O(aq) FeSO4(s) + 7H2O(l) Ans : [CBSE 2012]
(Pale green) (Dirty white)
a. Oxidation reaction
51. Translate the following statement into chemical b. Double displacement reaction
equation and then balance it. “A metal in the form of c. Combination reaction
ribbon burns with a dazzling white flame and changes d. Displacement reaction
into white powder.”
Ans : [CBSE 2013] 57. Write balanced equation for the reaction between Mg
Burning
and hydrochloric acid. Name the product obtained,
2Mg(s) + O2(g) 2MgO(s) + Light + Heat identify the type of reaction.
52. It has been found that marble of Taj is getting corroded Ans : [CBSE 20i2]
due to development of industrial areas around it. Mg(s) + 2HCl(dil) $ MgCl2(aq) + H2(g)
Explain this fact giving a chemical equation. Magnesium chloride and hydrogen gas are formed in
Ans : [CBSE 2013] this reaction. It is a displacement reaction.
Taj is made up of CaCO3 which reacts with acid 58. a. What is colour of ferrous sulphate crystals? How
formed by pollution of SO2(g) and NO2 from Mathura does this colour change after heating?
refinery and other industries. b. Name the products formed on strongly heating
CaCO3 + 2H2SO4 $ CaSO4 + CO2 + 2H2O ferrous sulphate crystals. What type of chemical
CaCO3 + 2HNO3 $ Ca(NO3)2 + H2O + CO2 reaction occurs in this change?
53. Consider the chemical equations given below and Ans : [CBSE 2012.2009]
a. FeSO 4 $ 7H 2 O crystals are pale green in colour.
 They become dirty white on heating. 64. Translate the following statements into chemical
b. Ferric oxide, sulphur dioxide and sulphur trioxide equations and then balance them:
are formed: a. Hydrogen gas combines with nitrogen to form
Heat
2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g) ammonia.
It is a decomposition reaction. b. Hydrogen sulphide gas burns in air to give water
and sulphur dioxide.
59. Reaction of compound X with aluminium is used to c. Barium chloride reacts with aluminium sulphate
join railway tracks or cracked machine parts. to give aluminium chloride and a precipitate of
a. Identify the compound. barium sulphate. State the two types in which
b. Name the reaction. this reaction can be classified.
c. Write a balanced chemical equation for the d. Potassium reacts with water to give potassium
reaction. hydroxide and hydrogen gas.
Ans : [CBSE 2012] Ans : [CBSE 2012]
a. The compound X is Fe2O3 (Ferric oxide) or Iron a. 3H2(g) + N2(g) $ 2NH3(g)
(III) oxide. b. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g)
b. It is called Thermite Reaction. c. 3BaCl 2 (aq) + Al 2 (SO 4) 3 (aq) $ 3BaSO 4 (s) + 2AlCl 3 (aq)
Heat
c. 2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l) This reaction can be classified as a double
displacement reaction as the two reacting species
60. Using balanced chemical equation explain the (BaSO4, Al2SO4)3 undergoes mutual exchange
difference between a displacement reaction and a of ions. It can also be classified as precipitation
double displacement reaction. reaction, since a white ppt. of BaSO4 is obtained.
Ans : [CBSE 2012, 2011] d. 2K(s) + 2H2O(l) $ 2KOH(aq) + H2(g)
Displacement reaction: A reaction in which a more
65. When a metal X is added to salt solution of metal Y,
reactive element displaces a less reactive element from
the following chemical reaction takes place:
its salt solution e.g.,
2KBr(aq) + Cl2(g) $ 2KCl(aq) + Br2(aq) Metal X + Salt solution of Y $
Double displacement reaction: A reaction in which Salt solution of X + Metal Y
two compounds exchange their ions to form two new Mention the inference you draw regarding the
compounds e.g., reactivity of metal X and Y and also the type of
KOH + HNO3 $ KNO3 + H2O reaction. State the reason of your conclusions.
61. Give an example each for thermal decomposition Ans : [CBSE 2012]
and photochemical decomposition reactions. Write X is more reactive than Y because , X displaces Y from
balanced chemical equation also. its salt solution. Hence, this reaction is an example of
Ans : [CBSE 2012] displacement reaction.
Thermal decomposition: 66. Identify the type of each of the following reactions:
Heat
ZnCO3(s) ZnO(s) + CO2(g) a. A reaction in which a single product is formed
Photochemical decomposition: from two or more reactants.
sunlight
2AgI(s) 2Ag(s) + I2(g) b. The reaction mixture becomes warm.
c. An insoluble substance is formed.
62. Why are decomposition reactions called the opposite d. External surface of the container in which reaction
of combination reactions? Give chemical equations for takes place becomes cold.
these reactions. Ans : [CBSE 2012]
Ans : [CBSE 2012]
a. Combination reaction
In decomposition reactions, a compound is broken b. Exothermic reaction
down into one or more elements or compounds e.g., c. Precipitation reaction (Double displacement
Heat
CaCO3(s) CaO(s) + CO2(g) reaction)
In combination reactions, two or more elements d. Endothermic reaction
or compounds combine to form a new compound.
Therefore, decomposition reactions are opposite to 67. A solution of potassium chloride when mixed with
combination reactions e.g., silver nitrate solution, an insoluble white substance is
3Mg(s) + N2(g)
Burns
Mg3N2(s) formed. Write the chemical reaction involved and also
mention the type of reaction.
63. Why does the colour of copper sulphate solution Ans : [CBSE 2012, 2011, 2010]
changes when an iron pin is dipped in it?
AgNO3(aq) + KCl(aq) $ AgCl(s)+KNO3(aq)
Ans : [CBSE 2012] (White ppt.)

It is a double displacement reaction.

Iron being more reactive displaces copper from copper
sulphate (Blue) solution to form iron (II) sulphate 68. Using a suitable chemical equation justify that some
(Pale green) solution and reddish brown copper metal chemical reactions are determined by
gets deposited. a. Change in colour.
Fe(s) + CuSO4 $ FeSO4(aq) + Cu(s) b. Change in temperature.
 Ans : [CBSE 2011] fumes and a white residue is left behind.
a. Change in colour: Blue coloured crystalline a. Name the salt.
copper sulphate crystals changes to white CuSO4 b. Write the equation for the decomposition reaction.
(anhydrous) on heating. Ans : [CBSE 2011]
Heat
CuSO4.5H2O CuSO4 + 5H2O a. Lead nitrate
(Blue) (Dirty white) Heat
b. 2Pb (NO 3) 3 (s) 2PbO (s) + 4NO 2 (g) + O 2 (g)
b. Change in temperature: (White) (Residue) (Brown)
CaO(s) + H2O(l) $ Ca(OH)2(aq) + Heat 74. When a solution of potassium iodide is added to a
solution of lead nitrate in a test tube, a reaction takes
69. (a) A solution of substance X is used for white
place.
washing. What is substance X? Write the chemical
a. What type of reaction is this?
reaction of X with water.
b. Write the balanced chemical equation to represent
(b) Why does the colour of copper sulphate solution
the above reaction.
changes when iron nail is dipped in it?
Ans : [CBSE 2011, 2010, 2008]
Ans : [CBSE 2011]
a. It is precipitation as well as double displacement
a. X is CaO, calcium oxide
reaction.
CaO(s) + H2O(l) $ Ca(OH)2(aq)
b. Pb (NO 3) (aq) + 2KI (aq) $ Pbl 2 (s) + 2KNO 3 (aq)
b. It is because Fe displaces Cu from CuSO4 (blue)
solution to form FeSO4 (pale green) and reddish 75. Define combination reaction. Give one example of a
brown Cu metal gets deposited. combination reaction which is also exothermic.
70. Balance the following reactions: Ans : [CBSE 2011]
a. BaCl2 + H2SO4 $ BaSO4 + HCl Combination reaction: The reaction in which two
b. Ca(OH)2 + HNO3 $ Ca(NO3)2 + H2O or more elements or compounds combine to form
c. Pb(NO3)2 $ PbO + NO2 + O2 compound(s) e.g.,
d. MnO2 + HCl $ MnCl2 + Cl2 + H2O C(s) + O2(g) $ CO2(g) + Heat
Ans : [CBSE 2011, 2009, 2008, 2008C] It is an exothermic, combination reaction.
a. BaCl 2 (aq) + H 2 SO 4 (dil) $ BaSO 4 (s) + 2HCl (aq) 76. What happens when an aqueous solution of sodium
b. Ca (OH) 2 (aq) + 2HNO 3 $ Ca (NO 3) 2 (aq) + 2H 2 O (l) sulphate reacts with an aqueous solution of barium
Heat
c. 2Pb (NO 3) 2 (s) 2PbO (s) + 4NO 2 (g) + O 2 (g) chloride? State the physical conditions of reactants in
d. MnO 2 + 4HCl $ MnCl 2 + Cl 2 + 2H 2 O which the reaction between them will not take place.
Write the balanced chemical equation for the reaction
71. Write the balanced equation for the following reactions and name the type of reaction.
and identify the type of reaction in each case: Ans : [CBSE 2016, 2010]
a. Potassium bromide + Barium iodide $ White precipitate of BaSO4 is formed.
Barium bromide + Potassium Iodide BaCl 2 (aq) + Na 2 SO 4 (aq) $ BaSO 4 (s) + 2NaCl (aq)
b. Hydrogen(g) + Chlorine(g) $ Hydrogen It is a double displacement reaction. If reactants are
chloride(g) taken in solid state, products will not be formed.
Ans : [CBSE 2011]
77. What is redox reaction? When a magnesium ribbon
a. 2KBr(aq) + BaI2 $ BaBr2(aq) + 2KI(aq) burns in air with a dazzling flame and forms a white
It is double displacement reaction. ash, is magnesium oxidised or reduced. Why?
sunlight
b. H2(g) +. Cl2(g) 2HCl(g) Ans : [CBSE 2010, 2009]
It is combination reaction.
Redox reaction is a reaction in which oxidation and
72. A zinc plate was put into solution of copper sulphate reduction takes place simultaneously.
kept in a glass container. It was found that blue colour Mg is getting oxidised because it is gaining oxygen
of the solution gets fader and fader with passage of to form magnesium oxide.
time. After few days when zinc plate was taken out of
the solution, a number of holes were observed on it. 78. Write any two observations in an activity which may
a. State the reason for the changes observed on zinc suggest that a chemical reaction has taken place. Give
plate. an example in support of your answer.
b. Write the chemical equation for the reaction Ans : [CBSE 2010]
involved.
a. Change in colour:
Ans : [CBSE 2011] AgNO 3 (aq) + KI (aq) $ AgI (s) + KNO 3 (aq)
(Yellow ppt)
a. Zinc displaces copper from copper sulphate
solution to form colourless ZnSO4 and copper b. Evolution of gas:
metal is deposited. Zinc gets consumed due to Zn(s) + H2SO4(aq) $ ZnSO4 (aq) + H2(g)
which holes are formed. 79. When the powder of common metal is heated in open
b. Zn(s) + CuSO4(aq) $ ZnSO4(aq) + Cu(s) china dish its colour turns black. However, when
73. A white salt on heating decomposes to give brown
hydrogen is passed over the hot black substance so
formed, it regains its original colour. Based on the
 above information answer the following questions: Oxidation reaction: The reaction in which O2 is added
a. What type of chemical reaction takes place in or H2 is removed or loss of electrons takes place is
each of the two given steps? called oxidation reaction. E.g.,
b. Name the metal initially taken in powdered form. 2Cu(s) + O2(g) $ 2CuO(s)
Write balanced equations for both the reactions. It is an exothermic reaction.
Ans : [CBSE 2010]
a. Oxidation reaction, Redox reaction THREE MARKS QUESTIONS
b. Copper metal was present initially
Heat
2Cu (s) + O 2 (g) CuO (s)
(Black) 85. Decomposition reactions require energy either in the
Heat
CuO (s) + H 2 (g) Cu (s) + H 2 O (l) form of heat, light or electricity for breaking down the
(Reddish brown)
reactants. Write an equation each for decomposition
80. Why do we store silver chloride in dark coloured reactions where energy is supplied in the form of heat,
bottle? Explain in brief. light and electricity.
Ans : [CBSE 2010] Ans : [CBSE 2018, 2014]
It is done so as to cut off the exposure to sunlight. a. CaCO3(s)
Heat
CaO(s) + CO2(g)
AgCl is photosensitive, it will decompose to Ag and sunlight
b. 2AgBr(s) 2Ag(s) + Br2(g)
Cl2 in the presence of sunlight. Electricity
sunlight c. 2H2O(l) 2H2(g) + O2(g)
2AgCl(s) 2Ag(s) + Cl2( g)
86. In the electrolysis of water:
81. “Oxidation and reduction processes occur
a. Name the gas collected at the cathode and anode
simultaneously”. Justify this statement with the help
respectively.
of example.
b. Why is volume of gas collected at one electrode
Ans : [CBSE 2010] double than that at the other? Name this gas.
Oxidation involves loss of electrons or addition of c. How will you test this gas?
oxygen. Whereas reduction involves gam of electrons Ans : [CBSE 2012, CBSE Sample Paper 2018]
or addition of hydrogen e.g.,
a. Hydrogen is collected at the cathode, oxygen is
collected at the anode.
b. It is because H2O contains hydrogen and oxygen
in the ratio 2 : 1.
c. Bring a burning matchstick near the gas, if the
H2 is getting oxidised to H2O, CuO is getting reduced gas burns with ‘pop’ sound, the gas is H2.
to Cu.
It shows oxidation and reduction occur simultaneously. 87. Define the term decomposition reaction. Give
one example each of thermal decomposition and
82. When magnesium ribbon bums in air or oxygen, a electrolytic decomposition reactions.
product is formed. State the type of chemical reaction Ans : [CBSE 2016]
and name the product formed in the reaction. Write
Decomposition reaction: The reaction in which a
balanced chemical equation for the reaction.
compound is broken down into simpler elements or
Ans : [CBSE 2009(C)] compounds:
Heat
It is a combination reaction. The product formed is a. CaCO3(s) CaO(s) + CO2(g)
magnesium oxide: b. 2H2O(l)
Electricity
2H2(g) + O2(g)
2Mg(s) + O2(g) $ 2MgO(s)
88. Name two salts that are used in black and white
83. Distinguish between a displacement reaction photography. Give equations for the reactions when
and a double displacement reaction. Identify the these are exposed to sunlight.
displacement and the double displacement reaction Ans : [CBSE 2016]
from the following reactions:
a. HCl(aq) + NaOH(aq) $ NaCl(aq) + H2O(l) AgBr (Silver bromide) and AgI (Silver iodide) are
b. Fe(s) + CuSO4(aq) $ FeSO4(aq) + Cu(s) used in black and white photography.
sunlight
Ans : [CBSE 2009] 2AgBr(s) 2Ag(s) + Br2(g)
sunlight
2AgI(s) 2Ag(s) + I2(g)
Displacement Reaction: When a more reactive metal
displaces a less reactive metal from its salt solution. 89. State one example each characterised by following
Double displacement reaction: When two compounds along with suitable chemical equation.
exchange their ions to form two new compounds. a. Change in state,
a. Double displacement reaction. b. Evolution of gas,
b. Displacement reaction. c. Change in temperature.
84. What is an oxidation reaction? Give an example of Ans : [CBSE 2016]
oxidation reaction. Is oxidation an exothermic or an a. Change in state:
endothermic reaction? AgNO3(aq) + HCl(aq) $ AgCl(s) + HNO3(aq)
Ans : [CBSE 2009] b. Evolution of gas:
 CaCO3 ^ s h + 2HCl ^dilh $ CaCl 2 ^aqh + H 2 O ^ l h + CO2 ^g h 95. In a schematic diagram for the preparation of hydrogen
c. Change in temperature: gas as shown in the figure. What would happen if the
d. CH4(g) + 2O2(g) $ CO2(g) + 2H2O(l) + Heat following changes are made

90. Name the type of reactions represented by the

following equations:
a. CaO + H2O $ Ca(OH)2
b. 3BaCl2 + Al2(SO4) $ 3BaSO4 + 2AlCl3
Heat
c. 2FeSO4 Fe2O3 + 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 a. In place of zinc granules, same amount of zinc
each. dust is taken in the test tube?
a. Change in colour, b. Instead of dilute sulphuric, dilute hydrochloric
b. Change in tem-perature, acid is taken?
c. Formation of precipitate. c. Sodium hydroxide is taken in place of dilute
Ans : [CBSE 2015] sulphuric acid and the flask is heated?
a. Change in colour: Ans : [CBSE 2014, 2010]
Zn (s) + FeSO 4 (aq) $ ZnSO 4 (aq) + Fe (s) a. Zinc dust will react faster, H2(g) will be liberated
Pale green (Colourless)
at a faster rate.
b. Change in Temperature:
b. Same volume of H2(g) will be formed.
2Mg + O2(g) $ 2MgO(s) + Heat
c. On heating Zn with NaOH, hydrogen gas will be
c. Formation of precipitate:
formed at a faster rate.
Pb (NO 3) 2 (aq) + 2HCl (dil) $ Pbcl 2 (s) + 2HNO 3 (aq)
White ppt
96. (a) Why is it necessary to balance a chemical
92. State the type of chemical reactions and chemical
equation?
equations that take place in the following:
(b) Write the balanced chemical equation for the
a. Magnesium wire is burnt in air.
following reactions:
b. Electric current is passed through water.
(i) Natural gas burns in air to form carbon
c. Ammonia and hydrogen chloride gases are mixed.
dioxide and water.
Ans : [CBSE 2015] (ii) During respiration, glucose combines with
a. 2Mg(s) + O2(g) $ 2MgO(s); oxygen and forms carbon dioxide and water
b. Oxidation reaction along with the release of energy.
c. 2H2O(l) $ 2H2(g) + O2(g); Ans : [CBSE 2013]
Decomposition reaction
a. Chemical equation must be balanced so as to
d. NH3(g) + HCl(g) $ NH4Cl(s);
follow the law of conservation of mass.
Combination reaction
b. (i) CH4(g) + 2O2(g) $ CO2(g) + 2H2O(l)
93. Write the balanced chemical equations for the (ii) C 6 H 12 O 6 (s) + 6O 2 (g) $ 6CO 2 (g) + 6H 2 O (l) + Heat
following chemical reactions:
97. (i) Solid calcium oxide was taken in a container and
a. Hydrogen + Chlorine $ Hydrogen Chloride
water was added slowly to it.
b. Lead + Copper Chloride $ Lead chloride +
(a) Write the observations.
Copper
(b) Write the chemical formula of the product
c. Zinc oxide + Carbon $ Zinc + Carbon
formed.
Monoxide
(ii) What happens when carbon dioxide is bubbled
Ans : [CBSE 2013] through lime water (a) in small amount (b) in
a. H2(g) + Cl2(g) $ 2HCl(g) excess?
b. Pb(s) + CuCl2(aq) $ PbCl2(s) + Cu(s) Ans : [CBSE 2013, 2012, 2010]
c. ZnO(s) + C(s) $ Zn(s) + CO(g)
(i) (a) The container becomes hot and hissing sound
94. Write chemical equations for the reactions taking is produced.
place when (b) Ca(OH)2 is the formula of the product formed.
a. Iron reacts with steam (ii) (a) Lime water turn milky when CO2(g) is passed
b. Magnesium reacts with dil. HCl through it:
c. Copper is heated in air Ca(OH)2(aq) + CO2(g) $ CaCO3(s) + H2O(l)
(b) If excess of CO2 is passed milkiness disappears:
Ans : [CBSE 2014]
CaCO3(s) + CO2(g) + H2O(s) $ Ca(HCO3)2(aq)
a. 3Fe(s) + 4H2O(g) $ Fe3O4(s) + 4H2(g)
b. Mg(s) + 2HCl(dil) $ MgCl2(aq) 98. Write the balanced chemical equation for the following
c. 2Cu(s) + O2(g) $ 2CuO(s)
 reaction and identify the type of reaction. CuO(s) + Zn(s)
heat
Cu(s) + ZnO(s)
Thermite reaction, iron (III) oxide reacts with Ans : [CBSE 2011]
aluminium and give molten iron and aluminium oxide.
a. In respiration, energy is released, therefore, it is
Ans : [CBSE 2012]
considered an exothermic reaction.
Fe2O3(s) + 2Al(s) $ Al2O3(s) + 2Fe(l) b. Oxidation involves addition of O2 or loss of
It is displacement as well as redox reaction. electrons. Reduction involves addition of H2 or
gain of electrons.
99. An aqueous solution of metal nitrate ‘P’ reacts with
c. Zn is getting oxidised, CuO is getting reduced.
sodium bromide solution to form yellow precipitate
‘Q’ which is used in photography. ‘Q’ on exposure 104. Write balanced chemical equations for the following
to sunlight undergoes decomposition to form metal reactions:
present along with a reddish brown gas. Identify ‘P’ a. Hydrogen sulphide gas burns in air to give water
and ‘Q’ write the balanced chemical equation for the and sulphur dioxide.
chemical reaction. List the two categories in which b. Barium chloride reacts with zinc sulphate to give
reaction can be placed. zinc chloride and barium sulphate.
Ans : [CBSE 2012] c. Natural gas bums in air to form carbon dioxide
‘P’ is silver nitrate (AgNO3) and water.
AgNO3(aq) + NaBr(ag) $ AgBr(s) + NaNO3(aq) Ans : [CBSE 2011]
(P) (Yellow ppt)

This reaction is categorised as double displacement as a. 2H2S(g) + 3O2(g) $ 2H2O(l) + 2SO2(g)

well as precipitation reaction. b. BaCl 2 (aq) + ZnSO 4 (aq) $ BaSO 4 (s) + ZnCl 2 (aq)
sunlight c. CH4(g) + 2O2 $ CO2(g) + 2H2O(l)
2AgBr(s) 2Ag(s) + Br2(g)
The above reaction is photochemical decomposition
reaction. FIVE MARKS QUESTIONS
100. A green coloured hydrated metallic salt on heating
loses water of crystallisation molecules and gives a gas 105. Write balanced chemical equation for the following
with suffocating smell. Identify the salt and write the statements:
chemical equation for the reaction. a. NaOH solution is heated with zinc granules.
Ans : [CBSE 2011] b. Excess of carbon dioxide is passed through lime
water.
The salt is FeSO 4 $ 7H 2 O (Hydrated ferrous sulphate)
Heat c. Dilute sulphuric acid is added to sodium carbonate.
FeSO 4 $ 7H 2 O FeSO 4 (s) + 7H 2 O (l)
Heat d. Egg shell is dropped in hydrochloric acid,
2FeSO 4 (s) Fe 2 O 3 (s) + SO 2 (g) + SO 3 (g) e. Copper (II) oxide reacts with dilute hydrochloric
acid.
101. a.Can combination reaction be an oxidation
reaction? Ans : [CBSE 2016]
b. How will you test whether the gas evolved in a a. Zn(s) + 2NaOH $ Na2ZnO2 + H2
reaction is hydrogen? b. Ca(OH)2 + 2CO2 $ Ca(HCO3)2
c. Why does copper not evolve hydrogen on reacting c. Na2CO3 + H2SO4 $ Na2SO4 + H2O + CO2
with dilute sulphuric acid? d. CaCO3(s) + 2HCl(dil) $ CaCl2 + H2O + CO2
Ans : [CBSE 2011] e. CuO(s) + 2HC1 $ CuCl2 + H2O
a. Yes, combination reaction can be called a 106. Identify the type of chemical reaction in the following
oxidation reaction. statement and define each of them:
b. Bring a burning splinter near the gas, if it burns a. Digestion of food in our body.
with pop sound, it is hydrogen gas. b. Rusting of iron.
c. It is because copper is less reactive than hydrogen. c. Heating of manganese dioxide with aluminium
powder.
102. Write balanced equations for the following reactions:
d. Blue colour of copper sulphate solution disappears
a. Aluminium + Bromine $ Aluminium bromide
Heat when iron filings are added to it.
b. Calcium carbonate
e. Dilute hydrochloric acid is added to sodium
Calcium oxide + Carbon dioxide hydroxide solution to form sodium chloride and
sunlight
c. Silver chloride Silver + Chlorine water.
Ans : [CBSE 2011] Ans : [CBSE 2016]
a. 2Al(s) + 3Br2(g) $ 2AlBr3(s) a. Decomposition reaction: It is a process in which a
Heat
b. CaCO3(s) CaO(s) + CO2(g) compound is broken down into simple substances.
c. 2AgCl(s)
sunlight
2Ag(s) + Cl2(g) b. Oxidation: The process in which oxygen is added
or electrons are lost.
103. a.Why is respiration considered an exothermic c. Displacement reaction: The reaction in which a
reaction? more reactive element can displace a less reactive
b. Define the terms oxidation and reduction, element from its salt solution. Oxidation and
c. Identify the substance that is oxidised and reduced Reduction are taking place simultaneously in
in the following reaction: rusting of iron.
 d. Displacement reaction: The reaction in which a surface of copper powder turns black.
more reactive element can displace a less reactive c. On heating green coloured ferrous sulphate
element. crystals, raddish brown solid is left and smell
e. Neutralisation reaction: The reaction in which of a gas having odour of burning sulphur is
acid reacts with base to form salt and water. experienced.
d. Iron nails when left dipped in blue copper sulphate
107. Define chemical reaction. State four observations solution become reddish brown in colour and the
which helps to determine whether a chemical reaction blue colour of copper sulphate fades away.
has taken place or not. Write one example of each e. Quick lime reacts vigorously with water releasing
observation with a balanced chemical equation. a large amount of heat.
Ans : [CBSE 2015] Ans : [CBSE Sample Paper 2009]
Chemical reaction is a reaction which represents a a. Double displacement reaction,
chemical change. b. Oxidation,
a. Change in colour: c. Decomposition reaction,
Cu (s) + 2AgNO 3 (aq) $ Cu (NO 3) (aq) + 2Ag (s) d. Displacement reaction,
(Colourless) (Blue)
b. Evolution of gas: e. Combination reaction.
Heat
CaCO 3 (s) CaO (s) + CO (g)
(Carbon dioxide gas
c. Formation of precipitate:
Pb (NO 3) 2 (aq) + 2KI $ PbI 2 (s) KNO 3 (aq)
(Yellow ppt)
d. Change in temperature:
CaO(s) + H2O(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) + 2H2O(l)
(iii) C6H12O6(s) + 6O2(g) $ 6CO2(g) + 6H2O(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]
Heat
a. (i) CaCO3(s) CaO(s) + CO2(g)
sunlight
(ii) 2AgBr(s) 2Ag(s) + Br2(g)
Electricity
(iii) 2H2O(l) 2H2(g) + O2(g)
b. Copper can displace Ag from AgNO3(aq) solution
because Cu is more reactive than Ag.
Cu (s) + 2AgNO 3 (aq) $ Cu (NO 3) 2 (aq) + 2Ag (s)

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