Lesson: Chemical Reactions
and Equations
Question 1
Which
of the following is not a physical change?
(a)
Boiling of water to give water vapour
(b)
Melting of ice to give water
(c)
Dissolution of salt in water
(d)
Combustion of Liquefied Petroleum Gas (LPG)
Solution:
(d)
Question 2
The
following reaction is an example of a:
(i) Displacement
reaction
(ii) Combination
reaction
(iii) Redox
reaction
(iv) Neutralisation
reaction
(a) (i) and (iv)
(b)
(ii) and (iii)
(c)
(i) and (iii)
(d)
(iii) and (iv)
Solution:
(c)
Question 3
Which
of the following statements about the given reaction are correct?
(i)
Iron metal is getting oxidised
(ii)
Water is getting reduced
(iii)
Water is acting as reducing agent
(iv)
Water is acting as oxidising agent
(a) (i), (ii) and (iii)
(b)
(iii) and (iv)
(c)
(i), (ii) and (iv)
(d)
(ii) and (iv)
Solution:
(c)
Question 4
Which
of the following are exothermic processes?
(i)
Reaction of water with quick lime
(ii)
Dilution of an acid
(iii)
Evaporation of water
(iv)
Sublimation of camphor (crystals)
(a) (i) and (ii)
(b)
(ii) and (iii)
(c)
(i) and (iv)
(d)
(iii) and (iv)
Solution:
(a)
Question 5
Three
beakers labelled as A, B and C each containing 25 ml of water was taken. A
small amount of , anhydrous and were
added to the beakers A, B and C respectively. It was observed that there was an
increase in the temperature of the solutions contained in beakers A and B,
whereas in case of beaker C, the temperature of the solution falls. Which one
of the following statement(s) is(are) correct?
(i)
In beakers A and B, exothermic process has occurred.
(ii)
In beakers A and B, endothermic process has occurred.
(iii)
In beaker C exothermic process has occurred.
(iv)
In beaker C endothermic process has occurred.
(a) (i) only
(b)
(ii) only
(c)
(i) and (iv)
(d)
(ii) and (iii)
Solution:
(c)
Question 6
A
dilute ferrous sulphate solution was gradually added to the beaker containing
acidified permanganate solution. The light purple colour of the solution fades
and finally disappears. Which of the following is the correct explanation for
the observation?
(a)
is
an oxidising agent, it oxidises
(b)
acts
as an oxidising agent and oxidises
(c)
The colour disappears due to dilution; no reaction is involved
(d) is
an unstable compound and decomposes in presence of to
a colourless compound.
Solution:
(a)
Question 7
Which
among the following is(are) double displacement reaction(s)?
(i)
(ii)
(iii)
(iv)
(a) (i) and (iv)
(b)
(ii) only
(c)
(i) and (ii)
(d)
(iii) and (iv)
Solution:
(b)
Question 8
Which
among the following statement(s) is(are) true? Exposure of silver chloride to
sunlight for a long duration turns grey due to
(i)
The formation of silver by decomposition of silver chloride
(ii)
Sublimation of silver chloride
(iii)
Decomposition of chlorine gas from silver chloride
(iv)
Oxidation of silver chloride
(a) (i) only
(b)
(i) and (iii)
(c)
(ii) and (iii)
(d)
(iv) only
Solution:
(a)
Question 9
Solid
calcium oxide reacts vigorously with water to form calcium hydroxide accompanied
by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form
its solution called lime water. Which among the following is(are) true about
slaking of lime and the solution formed?
(i)
It is an endothermic reaction
(ii)
It is an exothermic reaction
(iii)
The pH of the resulting solution will be more than seven
(iv)
The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b)
(ii) and (iii)
(c)
(i) and (iv)
(d)
(iii) and (iv)
Solution:
(b)
Question 10
Barium
chloride on reacting with ammonium sulphate forms barium sulphate and ammonium
chloride. Which of the following correctly represents the type of the reaction
involved?
(i)
Displacement reaction
(ii)
Precipitation reaction
(iii)
Combination reaction
(iv)
Double displacement reaction
(a) (i) only
(b)
(ii) only
(c)
(iv) only
(d)
(ii) and (iv)
Solution:
(d)
Question 11
Electrolysis
of water is a decomposition reaction. The mole ratio of hydrogen and oxygen
gases liberated during electrolysis of water is
(a)
1:1
(b)
2:1
(c)
4:1
(d)
1:2
Solution:
(b)
Question 12
Which
of the following(s) is(are) an endothermic process(es)?
(i)
Dilution of sulphuric acid
(ii)
Sublimation of dry ice
(iii)
Condensation of water vapours
(iv)
Evaporation of water
(a) (i) and (iii)
(b)
(ii) only
(c)
(iii) only
(d)
(ii) and (iv)
Solution:
(d)
Question 13
In
the double displacement reaction between aqueous potassium iodide and aqueous
lead nitrate, a yellow precipitate of lead iodide is formed. While performing
the activity if lead nitrate is not available, which of the following can be
used in place of lead nitrate?
(a)
Lead sulphate (insoluble)
(b)
Lead acetate
(c)
Ammonium nitrate
(d)
Potassium sulphate
Solution:
(b)
Question 14
Which
of the following gases can be used for storage of fresh sample of an oil for a
long time?
(a)
Carbon dioxide or oxygen
(b)
Nitrogen or oxygen
(c)
Carbon dioxide or helium
(d)
Helium or nitrogen
Solution:
(d)
Question 15
The
following reaction is used for the preparation of oxygen gas in the laboratory
Which
of the following statement(s) is(are) correct about the reaction?
(a)
It is a decomposition reaction and endothermic in nature.
(b)
It is a combination reaction.
(c)
It is a decomposition reaction and accompanied by release of heat.
(d)
It is a photochemical decomposition reaction and exothermic in nature.
Solution:
(a)
Question 16
Which
one of the following processes involves chemical reactions?
(a)
Storing of oxygen gas under pressure in a gas cylinder.
(b)
Liquefaction of air.
(c)
Keeping petrol in a china dish in the open.
(d)
Heating copper wire in presence of air at high temperature.
Solution:
(d)
Question 17
In
which of the following chemical equations, the abbreviations represent the
correct states of the reactants and products involved at reaction temperature?
(a)
(b)
(c)
(d)
Solution:
(d)
Question 18
Which
of the following are combination reactions?
(i)
(ii)
(iii)
(iv)
(a) (i) and (iii)
(b) (iii) and (iv)
(c)
(ii) and (iv)
(d)
(ii) and (iii)
Solution:
(d)
Question 19
Write
the balanced chemical equations for the following reactions and identify the
type of reaction in each case.
(a) Nitrogen
gas is treated with hydrogen gas in the presence of a catalyst at 773K to form
ammonia gas.
(b) Sodium hydroxide
solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is
warmed with ethanoic acid to form ethyl acetate in the presence of concentrated
.
(d) Ethene is
burnt in the presence of oxygen to form carbon dioxide, water and releases heat
and light.
Solution:
(a)
Reaction type: Combination reaction
(b)
Reaction type: Double displacement
reaction/Neutralisation reaction
(c)
Reaction type: Double displacement
reaction/Esterification reaction
(d)
Reaction type: Redox
reaction/Combustion reaction
Question 20
Write
the balanced chemical equations for the following reactions and identify the
type of reaction in each case.
(a) Thermite
reaction, iron (III) oxide reacts with aluminium and gives molten iron and
aluminium oxide.
(b) Magnesium
ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium
nitride.
(c) Chlorine
gas is passed in an aqueous potassium iodide solution to form potassium
chloride solution and solid iodine.
(d)
Ethanol is burnt in air to form carbon dioxide, water and releases heat.
Solution:
(a)
Reaction type: Displacement reaction/Redox reaction
(b)
Reaction type: Combination reaction
(c)
Reaction type: Displacement reaction
(d)
Reaction type: Redox reaction/Combustion reaction
Question 21
Complete
the missing components/variables given as x and y in the following reactions:
(a)
(b)
(c)
(d)
Solution:
(a)
(b)
(c)
(d)
Question 22
Which
among the following changes are exothermic or endothermic in nature?
(a)
Decomposition of ferrous sulphate.
(b)
Dilution of sulphuric acid.
(c)
Dissolution of sodium hydroxide in water.
(d)
Dissolution of ammonium chloride in water.
Solution:
(b) and (c) are
exothermic as heat is released in these changes.
(a) and (d) are
endothermic as heat is absorbed in these changes.
Question 23
Identify the reducing agent in the following
reactions
(a)
(b)
(c)
(d)
Solution:
(a) Ammonia
(b) Water as is getting
reduced to HF
(c)
Carbon monoxide
(d) Hydrogen
Question 24
Identify the oxidising agent (oxidant) in the following
reactions
(a)
(b)
(c)
(d)
(e)
(f)
Solution:
(a)
(b)
(c)
(d)
(e)
(f)
Question 25
Write the balanced chemical equations for the
following reactions:
(a) Sodium carbonate on reaction with hydrochloric acid in equal molar
concentrations gives sodium chloride and sodium hydrogen carbonate.
(b) Sodium hydrogen carbonate on reaction with hydrochloric acid gives
sodium chloride, water and liberates carbon dioxide.
(c) Copper sulphate on treatment with potassium iodide precipitates
cuprous iodide , liberates
iodine gas and also forms potassium sulphate.
Solution:
(a)
(b)
(c)
Question 26
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 the chemical reaction?
Solution:
It is a double
displacement and precipitation reaction.
Question 27
Ferrous sulphate decomposes with the evolution of a
gas having a characteristic odour of burning sulphur. Write the chemical reaction
involved and identify the type of reaction.
Solution:
It is a thermal
decomposition reaction.
Question 28
Why do fire flies glow at night?
Solution:
The protein
present in fire flies oxidizes in the presence of an enzyme. As a result, light
is emitted by the insect which appears as a glow in the darkness.
Question 29
Grapes hanging from the plant do not ferment but
after being plucked from the plant can be fermented. Under what conditions do
these grapes ferment? Is it a chemical or a physical change?
Solution:
When grapes are
attached to the plant, oxygen reaches the cells of the grapes and so aerobic
respiration takes place.
But when
plucked, oxygen cannot reach the cells of the grapes. This facilitates the
microbes to grow under anaerobic condition and it leads to fermentation.
It is a
chemical change.
Question 30
Which among the following are physical or chemical
changes?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot.
(d) Curdling of milk
(e) Sublimation of solid ammonium chloride
Solution:
Evaporation
of petrol, heating of an iron rod to red hot
and sublimation of solid ammonium chloride are physical changes.
Burning of
Liquefied Petroleum Gas (LPG) and
curdling of milk are
chemical changes.
Question 31
During the reaction of some metals with dilute
hydrochloric acid, following observations were made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises
when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be
highly explosive
(d) Some bubbles of a gas are seen when lead (Pb) is
reacted with
the acid.
Explain these observations giving suitable reasons.
Solution:
(a)
Silver metal does not react with dilute hydrochloric acid. Hence, there is no change.
(b) The
reaction between aluminium metal and dilute hydrochloric acid is an exothermic
reaction. Thus, the temperature of the reaction mixture rises when aluminium is
added to hydrochloric acid.
(c) Sodium
is one of the most reactive metals and when it reacts with dilute hydrochloric acid, the
reaction is exothermic. Thus, the reaction of sodium metal and dilute hydrochloric acid is found
to be highly explosive.
(d) When
lead reacts with dilute hydrochloric acid, hydrogen gas is evolved. Given below
is the chemical reaction:
Question 32
A substance X, which is an oxide of a group 2
element, is used intensively in the cement industry. This element is present in
bones also. On treatment with water it forms a solution which turns red litmus
blue. Identify X and also write the chemical reactions involved.
Solution:
The
substance X is Calcium oxide.
Question 33
Write a balanced chemical equation for each of the
following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to
form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium
ethoxide and hydrogen gas.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form
solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur
and liquid water.
Solution:
(a); Double displacement reaction
(b) ; Displacement reaction.
(c); Redox reaction.
(d) ; Redox reaction.
Question 34
Why do we store silver chloride in dark coloured
bottles?
Solution:
On exposure to sunlight, the silver chloride may
decompose as per the following reaction.
Therefore, it is stored in dark coloured bottles.
Question 35
Balance the
following chemical equations and identify the type of chemical reaction.
(a)
(b)
(c)
(d)
(e)
(f)
Solution:
(a) The
equation is already balanced; it is a combination reaction.
(b) ; it is a decomposition reaction.
(c) ; it is a combination reaction.
(d) ; it is a displacement reaction.
(e) The
equation is already balanced; it is a combination reaction.
(f) ; it is a decomposition reaction.
Question 36
A magnesium ribbon is burnt in oxygen to give a
white compound X accompanied by emission of light. If the burning ribbon is now
laced in an atmosphere of nitrogen, it continues to burn and forms a compound
Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is
dissolved in water.
Solution:
(a) When magnesium ribbon burns in oxygen, the chemical
equation of the reaction is:
Here the white compound X is magnesium oxide.
If
magnesium ribbon burns in an atmosphere that has only nitrogen, the reaction
would be:
The compound formed would be magnesium nitride.
(b) When X, i.e. magnesium oxide is dissolved in water,
magnesium hydroxide is formed. The chemical equation of the reaction is:
Question 37
Zinc liberates hydrogen gas when reacted with dilute
hydrochloric acid, whereas copper does not. Explain why?
Solution:
In the activity series of metals, zinc is placed above
hydrogen. It means zinc is more reactive
than hydrogen. Thus, zinc reacts with hydrochloric acid and hydrogen gas is
evolved.
Copper, on the other hand, is placed below
hydrogen. It means copper is less reactive than hydrogen. Hence, copper does
not displace hydrogen from dilute hydrochloric acid.
Question 38
A silver article generally turns black when kept in
the open for a few days. The article when rubbed with toothpaste again starts
shining.
(a) Why do silver articles turn black when kept in
the open for a few days? Name the phenomenon involved.
(b) Name the black substance formed and gives its
chemical formula.
Solution:
a) When kept in the open
for a few days, the silver reacts
with the moisture, oxygen and gases present in the air. This phenomenon is
called corrosion. This black coating is formed when silver reacts with hydrogen
sulphide.
(b)
When silver reacts with hydrogen
sulphide present in
the air, the black substance formed is
silver sulphide; and its chemical formula is .
Question 39
On heating,
blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide
(black), oxygen gas and a brown gas X is formed.
(a) Write a
balanced chemical equation of the reaction.
(b) Identity
the brown gas X evolved.
(c) Identity
the type of reaction.
(d) What could
be the pH range of aqueous solution of the gas X?
Solution:
(a) When cupric nitrate is heated in a boiling tube,
copper oxide, oxygen gas and nitrogen dioxide are formed. Balanced chemical
equation of the referred reaction is:
(b) Nitrogen
dioxide is a brown coloured gas evolved in the reaction.
(c) This is an
example of a decomposition reaction.
(d) When nitrogen dioxide
dissolves in water, it forms nitric acid. Water has a pH value of 7 while pH of
an acid is less than 7. Therefore, the pH of the aqueous solution of the gas X
will be less than 7.
Question 40
Give the characteristic tests for the following
gases:
(a)
(b)
(c)
(d)
Solution:
(a) On reacting with carbon dioxide ,
lime water turns milky. This is due to the formation
of insoluble calcium carbonate.
(b) Sulphur dioxide gas reacts
with potassium permanganate solution (purple in colour) and makes it
colourless. This is due to the action of the reducing agent sulphur dioxide
(c) When we bring
a burning candle near the mouth of the test tube containing oxygen ,
the intensity of the flame increases. This confirms
the presence of oxygen, as oxygen supports burning.
(d) When a burning candle is brought near hydrogen,
it burns with a pop sound. This is the test for the presence of hydrogen gas.
Question 41
What happens when a piece of:
(a) Zinc metal is added to copper sulphate
solution?
(b) Aluminium metal is added to dilute hydrochloric
acid?
(c) Silver metal is added to copper sulphate
solution?
Also, write the balanced chemical equation if the
reaction occurs.
Solution:
(a) When a piece of zinc metal is added to copper
sulphate solution, it displaces copper from its solution. This happens because zinc
is more reactive than copper. Due to this reaction, a solution of zinc sulphate
is obtained.
(b) Aluminium is more reactive than hydrogen. So, when
a piece of aluminium metal is added to dilute hydrochloric acid, it displaces
hydrogen from the dilute hydrochloric acid solution and forms aluminium
chloride and hydrogen gas.
(c) As per the activity series, silver metal is less
reactive than copper. Silver cannot displace copper from its salt solution.
Therefore, no reaction takes place when a piece of silver is added to copper
sulphate solution.
Question 42
What happens when zinc granules are treated with
dilute solution of also write
the chemical equations if reaction occurs.
Solution:
(a)
When zinc
reacts with dilute zinc
sulphate is formed. The reaction is:
(b)
When zinc
reacts with dilute HCl, zinc chloride is formed. The reaction is:
(c)
When zinc
reacts with dilute , zinc nitrate, water and nitrous oxide are formed.
Reaction with dilute is
different as compared to other acids because nitric acid is an oxidising agent
and it oxidizes gas to form .
(d)
Zinc does not
react with NaCl solution.
(e)
When zinc
reacts with dilute NaOH solution, sodium zincate is formed. The reaction is:
Question 43
On adding a
drop of barium chloride solution to an aqueous solution of sodium sulphite, a white
precipitate is obtained.
(a) Write a
balanced chemical equation of the reaction involved.
(b) What other
name can be given to this precipitation reaction?
(c) On adding
dilute hydrochloric acid to the reaction mixture, white precipitate disappears.
Why?
Solution:
(a)
When a drop of
barium chloride solution is added to an aqueous solution of sodium sulphite,
barium sulphite and sodium chloride are formed. The balanced chemical equation
is:
(b)
This reaction
is also known as double displacement reaction.
(c)
is the
salt of a weak acid (sulfurous
acid). When a dilute acid such as is added
to barium sulphite, it produces a white precipitate of barium chloride water and
sulphur dioxide. Since is soluble
in water, the white precipitate disappears.
Question 44
You are
provided with two containers made up of copper and aluminium. You are also
provided with solutions of dilute In which
of the above containers these solutions can be kept?
Solution:
A) In copper
container
(a) Dilute : The solution of dilute can be
kept in a copper container as it does not react with dilute .
(b) Dilute : The solution of dilute nitric acid ( ) cannot
be kept in a copper container as nitric acid acts as a strong oxidising agent
and reacts with copper.
(c) : Zinc chloride can be kept in a copper container
as zinc is more reactive than copper (Cu) and so there is no possibility of a
displacement reaction.
(d) : can be
kept in a copper container as copper does not react with water.
(B) In aluminium
containers
(a) Dilute : The solution of dilute cannot be
kept in an aluminium container as aluminium will undergo reaction with the
solution of dilute .
(b) Dilute : The solution of dilute can be
kept in an aluminium container as aluminium gets oxidised by dilute to form a
layer of .
(c) : cannot be
kept in an aluminium container as aluminium is more reactive than zinc; so, it
can displace zinc ion from the solution.
(d) : Aluminium does not react with cold or hot water.
Therefore, water can be kept in an aluminium container.