Physical And chemical Change

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EXCERCISE (A)
1.
(a)
(b)
2.
3.
(a)
(b)
(c)
4.
(a)
(b)
5.
6.
7.
8.
Define
A physical change
A chemical change.
Classify the following as a physical or chemical change:
(a)
Ripening of fruit,
(b)
(c)
Charging a car battery,
(d)
(e)
Manufacture of salt from sea
(f)
water,
(g)
Butter getting rancid,
(h)
(i)
Growth of a tree,
(j)
(k)
Making of dry ice from carbon
(l)
dioxide gas,
(m)
Boiling of water,
(n)
Liquefying air,
Drying of wet clothes,
Making of curd from milk,
Heating of platinum wire,
Rusting of iron,
Bursting of water pipes in sever
winter
Burning of paper.
Which of the following is not a physical change ?
Freezing of water.
Powdered sulphur when heated gently.
Magnetising of a piece of iron.
Give four characteristics of :
A physical change
A chemical change
Differentiate between physical and chemical changes.
Show that a physical change can easily be reversed.
Explain which type of change occurs when water is electrolysed.
When hydrogen burns in air, the change is chemical. Give two reason to support this
assertion.
9.
Explain why the heating of ammonium chloride can be understood as the combination
of a physical as well as a chemical change. Give another example of the same type of
change.
10.
Give reasons to show that the following are chemical changes:
(a)
Burning of magnesium in air.
(b)
Adding of calcium of water.
11.
Name a substance which on heating, leaves no residue behind. Give an equation.
12.
How do the following help in burning about a chemical change ?
(a)
Pressure
(b)
Electricity
(c)
Light
(d)
Catalyst
(e)
Hear
Give an example in each case.
13.
What is the difference between dissolution of copper sulphate in water that of
granulated zinc in dil. Hydrochloric acid ?
14.
Explain why sublimation is regarded as a physical change and the slaking of lime a
chemical change.
15.
Freezing of water to ice and evaporation of water are both physical changes. Explain
16.
Explain
(a)
(b)
(c)
17.
18.
(a)
(b)
(c)
(d)
When ammonium nitrate is dissolved in water contained in breaker, it becomes cold.
When little sulphuric acid is added to water in a beaker, it becomes hot.
Silver nitrate solution is kept in coloured reagent bottles in the laboratory.
Give reasons why burning of a candle is both a physical and a chemical change.
Complete the following statements by supplying the proper word or words:
The process of a liquid changing into a solid is called ...................
The temperature at which a solid changes into a liquid is called .........
The process of solid changing directly into a gas is called .......
A change which alters the composition of a substance is known as a ........ change.
EXERCISE 5(B)
1.
(a)
Define chemical reactions.
(b)
Give the conditions necessary for a chemical change or reaction.
2.
Define or explain the following terms:
(a)
(b)
(c)
3.
Chemical bond
Effervescence
Precipitate
State the main characteristics of chemical reactions. Give at least one example in each
case.
4.
Define exothermic and endothermic changes. Give two examples in each case.
5.
State the effect of an endothermic reaction and an exothermic reaction on the
surroundings.
6.
Give an example of reaction where the following are involved :
7.
Define
(a)
Photochemical reaction
(b)
Electrochemical reaction
Give on example in each case.
8.
Give an example of each of the following chemical change
(a)
A photochemical reaction involving
(i)
Silver half
(ii)
(b)
(i)
(ii)
(c)
(d)
Water
A reaction involving
Change of state
Formation of precipitate
An exothermic and endothermic reaction involving carbon as one of the reaction.
A reaction where colour change is noticed.
EXERCISE 5(C)
1.
What is a chemical reaction?
2.
3.
(a)
(b)
(c)
4.
5.
6.
7.
8.
(c)
9.
10.
11.
12.
13.
14.
(a)
(b)
(c)
15.
(a)
When hydrogen burns in oxygen, water is formed: when electricity is passed through
water, hydrogen and oxygen are given out . Name the type of chemical change involved
in the two cases.
Complete the following statements by supplying proper words.
The chemical change involving iron and hydrochloric acid illustrates a ............. reaction.
In the type of reaction called ......... two compounds exchange their positive and
negative radicals called ..........
A catalyst either .......... or ........... the rate of a chemical change but itself remains
............... at the end of the reaction.
Explain giving one simple example of each of the following chemical changes :
(a)
Double decomposition
(b)
Thermal dissociation
(c)
Electrolytic dissociation
(d)
displacement
What is synthesis? What king of chemical reaction is synthesis? Support your answer by
an example.
Decomposition brought about by heat is known as thermal decomposition. What is the
different between thermal dissociation and thermal decomposition?
Define neutralisation reaction. Give three application of neutralisation reaction.
(a) what do you understand by hydrolysis ? explain giving examples.
What is decomposition ? support your answer by an example.
Name the reaction in which rearrangement of atoms occurs. Give an example to
illustrate it.
Which type are the following reaction ?
(a)
2 +2KBr2KCI+B2
(b)
(c)
(e)
(g)
(i)
(k)
2HgO2HG+2
Ag3 +NaCIAgCI+Na3
22 222 +2
CuO+2 Cu+2 
N4 CI3 +HCI
(d)
(f)
(h)
(j)
 + 4 4
+ 
Pb2 +S2  4
2KCI3 2KCI+32
KN3 +2 4 HN3
CaC3 CaO+C2
Describe briefly the ionic concept of oxidation and reduction.
Is it essential that oxidation and reduction must occur side by side in a chemical
reaction ? explain.
State, giving reasons whether underlined substances have been oxidised or reduced.
PbO+COPb+C2
2 S+ 2 2HCI+S
State whether the following conversations are oxidation or reductiuon:
Pb2 +S2  4
(b)
16.
(a)
(b)
17.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
18.
(a)
(b)
(c)
(d)
(e)
(f)
K + + −
Give a chemical test for :
an oxidising agent
a reducing agent
Give an example of each of the following types of reaction:
An oxidation reaction involving removal of the electropositive element.
A redox reaction involving a metallic oxide and a neutral gas as the only reactants.
A catalytic reaction involving two gaseous reactants.
A decomposition reaction which does not require heat i.e. other thanthermal
decomposition.
An oxidation reaction involving addition of the electronegative redical.
A redox reaction involving two gases.
A photochemical reaction involving a silver salt.
Name
An oxidising agent which does not contain oxygen.
A substance which will oxidise concentrated HCI to chlorine.
A substance which will reduce aqueous iron (III) ions to Iron (II) ions.
A liquid which is an oxidising as well as reducing agent.
A gas which is an oxidising as well as reducing agent.
A solid which is an oxidising agent.
EXERCISE 5(D)
1.
(a) define burning
(b) air is necessary for burning. Comment.
2.
3.
4.
5.
6.
(a)
(b)
7.
(a)
(b)
8.
9.
(a)
(b)
10.
Why does magnesium gain weight on burning ?
Name the products formed when candle burns in the air. Give are test for each
product.
What are the conditions for burning to take place?
What do you understand by ignition temperature?
Explain
Why gun powder catches fire even in the absence of air.
Water can be boiled in a paper cup.
What are combustible and non-combustible substances ?
Name two substances other than oxygen that support combustion.
Define respiration. Give an experiment to show that respired air contains more carbons
dioxide than atmosphere air.
Compare the burning of carbon compounds with respiration.
How is respiration similar to burning?
Which gases are added to the air by :
(a)
(c)
11.
Decay or fermentation
Combustion
(b)
(d)
Respiration
Photosynthesis?
(b)
Respiration
Which gases are removed from the air by :
(a)
(c)
Photosynthesis
Combustion
12.
State two important processes which :
(a)
Release C2 into atmosphere
(b)
Remove C2 from atmosphere.
13.
How does the balance of 2 and C2 is manufactured in nature ?
14.
What will be the effect on :
(a)
Burning
(b)
Digestions
(c)
Metals,
If nitrogen is absent in air.
15.
What would be the effect on burning if the proportions of nitrogen and oxygen in the
air were reversed?
Other important questions
Short answer type questions
1.
State what would you observe and write equations for the reactions taking place when
: Zinc carbonate is heated in a test rube and the test tube is allowed to cool ?
2.
Which of the following are physical changes and which are chemical changes ?
(a)
(c)
(e)
(g)
(i)
(k)
(m)
3.
Freezing of water
A platinum wire glows red hot
in flame
Heating ammonium chloride
Onion sprouting
Fermentation of flour
Drying up plaster
Magnetising a piece of iron.
5.
6.
Dissolving sugar in water
Switching on an electric lamp
(f)
(h)
(j)
(l)
An iron nail gets rusted
Melting of ghee
Heating an electric iron
Making curd from milk
Give on example in each case :
(a)
(c)
4.
(b)
(d)
Combination reaction
Substitution reaction
(b)
(d)
Decomposition reaction
Double decomposition
reaction.
What is the difference between the dissolving copper sulphate in water and granulated
zinc in dilute hydrochloric acid ?
Respiration involves both physical and chemical changes. Justify.
Give three applications of reactions of neutralisation.
7.
Classify the following reactions :
(a)
(b)
(c)
(d)
(e)
(f)
Zn+2 4 (dil)  Zn 4 +2 (g)
BaCI(aq)+ 2 4 (aq) Ba 4 (s)-2NaCI
2CO+2 2 C2
2KN3 2KN2 +2
3Fe+42 () Fe4 +42
22 
22 () + 2 ))
(g)
2KCI3
(h)
(i)
2 + 2
2KCI+32
2HCI
8.
CuO+2
 + 2 
In the above equations, by giving reasons. Explain which substance is :
(a)
Oxidised
(b)
Reducing
(c)
Oxidising agent
(d)
Reducing agent.
9.
10.
11.
12.
13.
(a)
(b)
14.
15.
16.
17.
What do you understand by the term thermal dissociation? How is thermal
dissociation different from thermal decomposition ? write two fully balanced equations
for thermal dissociation reactions.
What is energy of activation ? suppose your answer by one example.
Define ‘energy change’ during a chemical reaction.
Which type are the following reactions
(a)
(b)
4 N3 +HCI
2 + 22KCI+2
(c)
(d)
2HgO2Hg+2
Fe+CuS2  Fe2 +Cu
(e)
(f)
AgN3 +
Ca3 CaO+C2
AgCI+Na
N3
(g)
(h)
2KCI3 2KCI+32
Pb2 +S2 PbS4
Give three examples in each case :
Oxidising agents
Reducing agents.
What is a reversible reaction ? what is the most important condition for the reversible
reaction to take place ? support your answer by a fully balanced chemical equation.
What is the difference between precipitation reaction and neutralisation reaction ?
which kind of chemical reactions belong to these reactions ? support your answer by
one example each.
What is analysis ? which kind of chemical reactions belong to analysis? Support your
answer by an example.
Indicate whether the given changes are physical or chemical changes.
18.
19.
20.
(a)
(b)
(c)
(d)
21.
(a)
(c)
(e)
(g)
(i)
(k)
making of wine
plucking of a fruit
evaporation of water
baking of cake
glowing of a tube light
burning of cooking gas
(b)
(d)
(f)
(h)
(j)
(l)
(m)
(o)
(q)
(s)
(u)
(w)
burning of petrol
drying of paint
Rusting of iron
ripeaning of iron
breaking of glass pane
fading of colour of a dyed cloth
(n)
(p)
(r)
(t)
(v)
(x)
formation of dew
production of biogas
magnetisation of iron
sublimation of dry ice
making of ice-cream
crystallisation of sugar from its
saturated solution
smoking of cigarette
ringing of an electric bell
dissociation of sugar in water
butter turning rancid
clotting of blood
milk sours in hot and humid
weather
When we mix iron filing with sulphur and grind it, a physical change takes place.
However, if we heat the mixture a chemical change takes place. Using the above
sample give your differences between physical and chemical changes.
When hydrogen burns in oxygen, water is formed; when electricity is passed through
water, hydrogen and oxygen are given out. Name the type of chemical change involved
in the two cases.
Which is not a physical change in the following changes :
Burning of a piece of magnesium wire in air.
Freezing of water.
Powdered sulphur when heated gently.
Boiling of water.
Give four characteristics of :
(a) Rusting of iron
(b) Digestion of food
22. A small piece of sodium is dropped into a beaker of water. Give two
reasons why the reaction involves a chemical change.
23. Name four physical constant
24. Explain why sublimation is regarded as a physical change while the
slaking of lime as a chemical change ?
25. Show that there is n no change in mass in a physical change.
26. What is a reactant and a product ?
27. What is atmospheric air ?
28. What do you know about the composition of air ?
29. What is the importance of dissolved air in water ?
30. Air contains nitrogen and oxygen. Name two other gases present in
air.
31. Why are percentage of nitrogen in air different by volume and by
mass ?
32. What happens what air is shaken with freshly boiled and cooled
water ?
33. Show that oxygen is present in air.
34. What is the biological importance of dissolved oxygen and carbon
dioxide in river water ?
35. A graduated tube containing some air stands inverted in water in a
beaker. Now a substance
X which is capable of reacting with oxygen is introduced .
(a) Name the substance X.
(b) If the tube originally contained 100cm3 of air, what would be the
composition and volume of air above the water when all the
oxygen had been remove ?
36. Name two substances formed during the combustion of candle.
37. Give the biological importance of nitrogen present in the air which
we breath.
38. The diagram given below illustrates a method of determining the
percentage of oxygen in air, using white phosphorus. After the
reaction has ceased the volume of the gas was found after levelling.
Answer the following questions :
(a) Name the main gas left behind after the experiment.
(b) What is the purpose of phosphorus ?
(c) What is the approximate percentage of oxygen in the air ?
39. When a piece of magnesium is burnt in air, its weight increase
whereas when a candle burns in air its weight decreases. Explain the
observation.
40. Explain why the fish and water plants can survive in river water, but
not in a stopered jar containing distilled water.
41. What are polluting gases ? what harm do they cause ?
42. By volume, which of the following is the amount of carbon dioxide in
pure air ?
(a) 0.03%
(b) 0.93%
(c) 78.09%
43. What is the ratio of nitrogen and oxygen in air ?
44. Which room will have pure air :
(a) Window and ventilators opened room.
(b) Windows and ventilators close room.
45. Which of the following is produced by burning organic substances :
(a) Oxygen
(b)
carbon dioxide (c) nitrogen.
46. Constituents of air can be separated by :
(a) Filtration
(c) crystallisation
(b) Liquefaction
(d) sublimation
47. Rewirte the following sentences after necessary corrections :
(a) Nitrogen supports combustion and oxygen controls combustion.
(b) During respiration we use nitrogen and give out hydrogen and
oxygen.
(c) Air contains 1/5 part of its volume as nitrogen and 4/5 part as
oxygen.
(d) Atmosphere air contains more carbon dioxide than exhaled air.
48. The table give below gives a summary of the element. You are
required to study this table and answer the questions that follow :
49. How is oxygen separated from air ?
50. When 2g of Mg is burnt in air the weight of resultant white powder
is much more than 2g, why ?
51. Name the principle oxide with each of the following :
52. Describe what do you observe and write equation for the actions
taking place when :
(a) Potassium nitrate is heated strongly in a test tube.
(b) Write an equation for reaction taking place when mercuric oxide
is headted.
53. Fill in the blanks :
(a) The air of industrial town has more ........... than the air of open
country.
(b) When the liquid air is allowed to evaporate ........ which has
lower boiling point evaporate leaving behind ............. .
(c) The substances which can be in air are called ........ while
substances which cannot burn in air are known as .............. .
54. How is air purified by plants ?
55. Air contains nitrogen and oxygen. Name the two other gases present
in air.
56. When air is passed through water for sometime, the percentage of
oxygen in water increase. Explain.
57. What is the significance of dissolved air in water ?
58. Name four substances capable of absorbing water vapours.
59. Why does anhydrous calcium chloride become sticky when exposed
to air ?
60. Why does gun powder burn without air upon heating strongly ?
61. Name the inert gases present in air. Why are they so called ?
62. Why proportion of nitrogen in both inspired air and expired air
remains the same ?
63. Why does proportion of carbon dioxide in air remains almost the
same although a large amount of fuel burns both in home and
factories ?
64. Why does mist appear on the surface of a glass plate when hold
over the flame of a burning candle ?
65. How do plants help in checking air pollution ?
66. Name the gases which are added to air by :
(a) Decay of fermentation
(b) Respiration
(c) Combustion
(d) Oxygen.
67. Name two major constituents of air other than oxygen and nitrogen
. describe how each of these can be identified.
68.
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