EXERCISES:-(Page:14-16)
1.Which of the reactions about the reaction below are
incorrect?
incorrect?
2PbO(s)+C(s)—>2Pb(s)+CO2(g)
a) Lead is getting oxidised
b) Carbon dioxide is getting oxidised
c) Carbon is getting oxidised
d) Lead oxide is getting reduced
ANSWER- (a)
2. Fe2O3+2Al—>Al2O3+2Fe
The above reaction is an example of a
a) Combination reaction
b) Double displacement reaction
c) Decomposition reaction
d) Displacement reaction
ANSWER-(d)
3. What happens when dilute hydrochloric acid is added
to iron fillings. Tick the correct answer.
to iron fillings. Tick the correct answer.
a) Hydrogen gas and iron
chloride is produced
chloride is produced
b) Chlorine gas and iron hydroxide are produced
c) No reaction takes place
d) Iron salt and water are produced
ANSWER-: (a)
4. What is balanced chemical equation? Why should
chemical equations be balanced?
chemical equations be balanced?
ANSWER-:The number of atoms of each element remains same
before and after reaction is known as balanced chemical equation.
before and after reaction is known as balanced chemical equation.
Chemical equations should be balanced so as to satisfy the law of
conservation of mass which states that mass can neither be created nor
destroyed.
conservation of mass which states that mass can neither be created nor
destroyed.
5. Translate the following statements into chemical
equations and balance them.
equations and balance them.
a) Hydrogen gas combines with nitrogen to form ammonia
b) Hydrogen sulphide gas burns in air to give water and sulpher
dioxide
dioxide
c) Barium Chloride reacts with aluminum sulphate to give aluminum
chloride and a precipitate of barium sulphate.
chloride and a precipitate of barium sulphate.
d) Potassium metal reacts with water to give potassium hydroxide
and hydrogen gas
and hydrogen gas
ANSWER- a)3H2(g)+N2(g)—>2NH3(g)
b)2H2S(g)+3O2(g)—>2H2O(L)+
2SO2(g)
2SO2(g)
c)3BaCl2(aq)+Al2(SO4)3(aq)—>2AlCl3(aq)+3BaSO4(s)
d)2K(s)+2H2O(l)—>2KOH(aq)+H2(g)
6.Balance the following chemical equations.
a)HNO3+Ca(OH)2—>Ca(NO3)2+
H2O
b)NaOH+H2SO4—>Na2SO4+H2O
c)NaCl+AgNO3—>AgCl+NaNO3
d)BaCl2+H2SO4—>BaSO4+HCl
ANSWER:-a) 2HNO3+Ca(OH)2—>Ca(NO3)2+
2H2O
b)2NaOH+H2SO4—>Na2SO4+
2H2O
2H2O
c)NaCl+AgNO3—>AgCl+NaNO3
d)BaCl2+H2SO4—>BaSO4+2HCl
7.Write the balanced chemical equations for the
following reactions.
following reactions.
a)Calcium hydroxide+Carbon dioxide—>Calcium Carbonate+Water
b)Zinc+Silver nitrate—>Zinc nitrate+Silver
c)Aluminium+Copper chloride—>Aluminium Chloride+Copper
d)Barium Chloride+Potassium Sulphate—> Barium
Sulphate+Potassium Chloride
Sulphate+Potassium Chloride
ANSWER:-a)Ca(OH)2+CO—>
CaCO3+H2O
CaCO3+H2O
b)Zn+2AgNO3—>Zn(NO3)2+2Ag
c)2Al+3CuCl2—->2AlCl3+3Cu
d)BaCl2+K2SO4—>BaSO4+2KCl
8. Write the balanced chemical equation for the
following and identify the type of reaction in each case.
following and identify the type of reaction in each case.
a)Potassium bromide(aq)+Barium iodide(aq)—>Potassium
iodide(aq)+Barium bromide(s)
iodide(aq)+Barium bromide(s)
b)Zinc carbonate(s)—>zinc oxide(s)+carbon dioxide(g)
c) Hydrogen(g)+Chlorine(g)—>hydrogen chloride(g)
d)Magnesium(s)+Hydrochloric acid(aq)—->Magnesium
chloride(aq)+Hydrogen(g)
chloride(aq)+Hydrogen(g)
ANSWER:-a) 2KBr(aq)+BaI2(aq)—> 2KI(aq)+BaBr2(s)
DOUBLE DISPLACEMENT
b) ZnCO3(s)—>ZnO(s)+CO2(g)
DECOMPOSITION
c)H2(g)+Cl2(g)—->2HCl(s)
COMBINATION
d)Mg(s)+2HCl(aq)—->MgCl2(aq)+
H2(g)
DISPLACEMENT
9)What does one mean by exothermic and endothermic
reactions?Give examples.
reactions?Give examples.
ANSWER-: Exothermic reaction is the type of chemical reaction
that releases energy by light or heat. Example-Burning of a substance,
Neutralization.
Neutralization.
Endothermic reaction is the type of reaction that absorbs energy but not always in the form of heat. Example-Melting of an ice, thermal
decomposition reactions.
decomposition reactions.
10. Why is respiration considered as an exothermic
reaction ? Explain
reaction ? Explain
ANSWER-: Respiration is known as exothermic reaction as because
in respiration oxidation of glucose takes place which produces a large amount
of heat energy.
in respiration oxidation of glucose takes place which produces a large amount
of heat energy.
C6H12O6(aq)+6O2(g)—>6CO2(g)+6H2O(L)+Energy
11.Why are decomposition reactions called the opposite
of combination reactions ?
of combination reactions ?
Write equations for these reactions.
ANSWER:-In a decomposition reaction a single substance
decomposes to give two or more substances whereas in combination reaction to or
more substance combine to form a single substance .Hence decomposition reaction
is called the opposite of combination reaction
decomposes to give two or more substances whereas in combination reaction to or
more substance combine to form a single substance .Hence decomposition reaction
is called the opposite of combination reaction
12. Write one equation each for decomposition reactions where energy is supplied in the form of
heat, light or electricity.
heat, light or electricity.
ANSWER:- 1.Heat energy CaCO3–heat–>CaO(s)+ CO2(g)
2.Light enegy:-2AgCl(s)—sunlight–>2Ag(s)+Cl2(g)
3.Electricity 2H2O(l)—electricity–>2H2(g)+O2(g)
13.What is the difference between displacement and
double displacement
double displacement
reactions? Write equations for these reactions.
ANSWER-:When an element displaces another element from its
compound displacement reaction occurs whereas in double displacement two different atoms or group of atoms are
exchanged
compound displacement reaction occurs whereas in double displacement two different atoms or group of atoms are
exchanged
Displacement-Fe(s)+ CuSO4—>FeSO4(aq)+Cu(s)
Double displacement-Na2SO4 (aq)+BaCl2(aq)—>BaSO4(s)+2NaCl(aq)
14. In the refining of silver, the recovery of silver from silver
nitrate solution involved displacement by copper metal. Write down the reaction
involved.
nitrate solution involved displacement by copper metal. Write down the reaction
involved.
ANSWER:-Cu(s)+2AgNO3(aq)—> Cu(NO3)2(aq)+2Ag(s)
15. What do you mean by a precipitation reaction? Explain
by giving examples..?
by giving examples..?
ANSWER:-Precipitation reaction is the type of reaction which
produces insoluble salts
produces insoluble salts
Na2SO4(aq)+BaCl2(aq)—>BaSO4(s)+NaCl(aq).
BaSO4 is insoluble in water and its a white precipitate
16. Explain the following in terms of gain or loss of
oxygen with two examples each.
oxygen with two examples each.
(a) Oxidation
(b) Reduction
ANSWER:-a) Oxidation- Oxidation is a chemical reaction in
which gain of oxygen or loss of hydrogen takes place
which gain of oxygen or loss of hydrogen takes place
b) Reduction-Reduction is a chemical reaction in which loss of
oxygen or gain of hydrogen takes place.
oxygen or gain of hydrogen takes place.
17. A shiny brown coloured element ‘X’
on heating in air becomes black in colour. Write the name the element ‘X’ and the black coloured compound formed.
on heating in air becomes black in colour. Write the name the element ‘X’ and the black coloured compound formed.
ANSWER:-
2Cu(s)+O2(g)—heat–>2CuO(s)
X-copper
Compound formed-Copper Oxide
18.Why do we apply paint on iron articles?
ANSWER:-
To prevent rusting we apply paint on iron articles as because
after painting iron does not come in contact with air and moisture and prevent
rusting.
after painting iron does not come in contact with air and moisture and prevent
rusting.
19.Oil and fat containing food items are flushed with
nitrogen. Why?
nitrogen. Why?
ANSWER:-Nitrogen acts as an oxidized and prevents them from
being oxidized so oil and fat containing food items are flushed with nitrogen.
being oxidized so oil and fat containing food items are flushed with nitrogen.
20. Explain the following terms with one example each.
a) corrosion
b) rancidity
ANSWER: Corrosion-:It is the process in which
when a metal is attacked by moisture, acids etc and the metal corrodes
when a metal is attacked by moisture, acids etc and the metal corrodes
b)rancidity:-It is the process in which when the substances
containing oils and fat which when exposed to air becomes rancid and their
taste and smell changes.
containing oils and fat which when exposed to air becomes rancid and their
taste and smell changes.