F
DS
L
AR
USE
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FO
R ALL
FOUNDATION & OLYMPIAD CLASS – 8
Solutions
BO
F O U N D AT IO N & O LY M P IA D CLASS - VIII
Solutions
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CONTENTS
` 1. States of Matter ..........................................
01
2. Symbols, Formulae & Equations ...............
07
3. Transformation of substances ...................
10
4. Atomic Structure ........................................
19
5. Water ...........................................................
25
6. Hydrogen & Oxygen ..................................
30
7. Carbon and its Compounds .......................
34
8. Metals and Non-metals ..............................
38
9. Synthetic fibres and Plastics ......................
42
IIT Foundation & Olympiad Explorer
Class – VIII / Chemistry/ Solutions
Chapter
States of Matter
SOLUTIONS 6.
MULTIPLE CHOICE QUESTIONS 1.
(B)
water etc., are colourless. While all forms of matter can have
When an equal amount of water is poured in containers of different
volume, mass and can be living or non living. Hence, all forms of
shapes, it takes the shape of the container used. Hence, the result
matter have colour is not a true statement.
of experiment shows that water has no definite shape. 2.
(A)
7.
According to the venn diagram, Z
8.
three states. Water exists as ice (solid), water (liquid) and water
9.
triple point of water. When the inter molecular space between the particles are
vibratory motion. 10.
the particles come closer to each other. (B) (B)
external pressure.
A common balance is used to 11.
Hydrogen is a gas and hence it has no definite shape nor volume. It
(C) Space between particles decreases from gases to solids gradually. Hence, the decreasing order of empty space between the particles
has only definite mass. 1. States of Matter
(C) Since the constituent particles are closely packed which cannot be brought further nearer to each other, by compressing using
determine the mass of a solid. 5.
(C) Solids have particles closely packed and cannot change their position and hence have only
decreased, the volume of the substance is decreased because
4.
(C) Mercury is a liquid at room temperature whereas iron, aluminium and steel are solids.
vapour or steam (gas) and also it can co-exist in all three states at (B)
(B) As the particles move apart, their inter particle attractive force decreases with increasing distance.
must exist in three states of matter as it is an intersection of all the
3.
(B) Some forms of matter like air, pure
1
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is gas, liquid and solid. The
12.
(B)
17.
Due to this, their inter molecular spaces decreases and inter
It is difficult to compress the solids
molecular forces of attraction increases.
since their particles are closely packed. Hence solids have least
18.
property of compressibility. 13.
(D) Gas particles move freely and they
gaseous state. Hence, I liquid, II solid and III gas.
maximum power of diffusion.
19.
(D) Solids have maximum densities as their particles are more closely 20.
than gases. The decreasing order of densities for a given mass is 21.
(A) When a solid melts, the intermolecular attractive forces between the molecules decreases and intermolecular spaces increases. Hence, the molecules move further.
22.
(C) Perfume is in a vapour state and it can diffuse readily than other liquids.
23.
(D) Petrol is volatile i.e., has the
Solids rigid than liquids and gases. Because solids have close packing with a definite position of molecules. Liquid and gases are fluids both. Hence, have ability to flow. Liquids have ability to exhibit compressibility due to presence of intermolecular spaces greater
tendency to evaporate faster than the other given liquids.
than solids. Gases have maximum comp-
24.
ressibility because of very loose packing of particles. 16.
(C)
(C) On condensation, water vapour loses energy and their particles come closer due to decrease in
Molecules come closer as the
inter molecular forces of attraction. Hence, have less
temperature decreases. Because K.E is proportional to temperature.
1. States of Matter
(D) Since the container is closed the molecules move more rapidly as they gain energy and pressure inside the container increases.
solid > liquid > gases. (B)
(C) Sodium chloride does not sublime, while ammonium chloride, dry ice and iodine undergo sublimation.
packed in a given volume. Liquids have relatively more close packing
15.
(C) Oil and paint exists in liquid state crayon and snow are in solid state while wind and oxygen exists in
diffuse more easily into one another. Hence, gases have 14.
(D) On cooling gases they lose energy.
tendency to flow increases from solids to gases gradually.
intermolecular spaces and are less free to move around. 2
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25.
(A)
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For the process A, the change of
3. (A,D)
made up of same material and ball A has greater mass. Since the pan
For the process B, the change of
with ball A moves downwards. This implies that the air inside
state is from liquid to gas. Hence, it is vaporisation.
Ball A is more compressed than air in ball B.
For the process C, the change of state is from gas to liquid. Hence,
4. (A,C,D) This experiment shows that object X is lighter than Y and liquid B is heavier than C since both objects
it is condensation. For the process D, the change of state is from liquid to solid. Hence,
are floating in B. Liquid C is lighter than A & B since both objects sink
it is solidification.
in it.
For the process E, the change of state is from solid to gas. Hence,
5. (B,C,D) As Meena pushed the bottle, water level in the bottle increases and air present in bottle gets pushed
it is sublimation.
into the tube which is bubbled out from the beaker. This experiment proves that air and water occupy
For the process F, the change of state is from gas to solid. Hence it is solidification of gaseous state or also known as hoar frost.
some space and only one matter can occupy space at any one time.
MULTIPLE ANSWER QUESTIONS 1. (C,D)
Two balls are of same size and
state is from solid to liquid. Hence, it is melting.
6. (A,B)
Since the biscuits are only crushed to smaller pieces which have definite shape and exist as solid. Varun can conclude that both X and
Milk is viscous than water. 7. (B,C)
Y have definite shape and exists in same state. 2. (A,B,C) As Venu blows air into the straw,
This experiment proves that cork is lighter than water and it occupies some space.
8. (A,C,D) Water has a fixed mass and definite volume and takes the shape of a container.
air bubbles escape into the beaker, pressure increases inside the beaker and pushes the water down. As a result water level in
9. (A,B,C) By taking fixed amount of liquid, fixed size of the container and fixed number of marbles or beads, the space occupied by them can be determined.
beaker decreases and increases in the basin.
1. States of Matter
Milk is a liquid and does not have any definite shape and it flows from higher level to lower level.
3
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10. (A,B,C) As the wooden rod, which is being
PARAGRAPH QUESTIONS
horizontal got disturbed on removing air from balloon P. It
2=II=CA`1 (i)
proves that air has mass. When air is filled into a balloon it occupies
watervapour falls down in the form of rain at low temperatures.
space. Air does not have definite shape as it occupies the shape of a balloon.
(ii)
(C)
It is difficult to cook food on hill top as the boiling point of water
white when cold. Initially, zinc carbonate under goes chemical
decreases at hills due to decrease in atmospheric pressure. 2.
(E)
change. Cooling of zinc oxide a goes physical change, to change its
Gases diffuse easily than liquids and solids. Because they have least
colour from yellow to white. (iii)
inter molecular attractions among the particles and greater inter(D) During the process of evaporation of liquid the temperature of the
different, when a chemical change occurs. Hence, both chemical and
liquid decreases because the surface molecules while
physical properties change. 2=II=CA`11
evaporating take some amount of energy from the other molecules
(i)
4.
5.
(A)
(C)
to
must be honey as it is formed by the intersection of definite volume
absolute
and no definite shape in the venn diagram.
Gases do not have free surfaces as their molecules move randomly in all directions.
(ii)
(A) Oxygen, being gas does not have definite volume nor definite shape. Hence, y must be a gas i.e., oxygen
Melting point of solid decreases by addition of soluble impurities. Hence, on sprinkling salt water, the ice melts at low temperature due to decrease in melting point and draining out ice as water.
1. States of Matter
(C) Honey has definite volume but no definite shape because it is a liquid at room temperature. Hence, x
of liquid. Thus, evaporation leads to cooling. Kinetic energy is proportional temperature.
(C) Along with formation of new substance with different properties, physical properties of the new substance will be
molecular spaces. 3.
(C) First zinc carbonate decomposes to give zinc oxide and CO2 and zinc oxide appears yellow when hot and
ASSERTION AND REASONING 1.
(B) Rain formation is a physical change because the condensed
which is formed by the intersection of no definite volume and shape in the venn diagram. 4
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5.
CONCEPTUAL QUESTIONS 1.
(a)
According to table given. (1) Matter A allows light to pass through while matter E does not allow light to pass through. Therefore, A is transparent object while E is opaque object.
6.
Sponge
is
lighter,
and
more
compressible. Both sponge and plasticine have definite mass and have volume.
(2) Matter A has definite shape while matter E does not have definite shape. (b)
Both cubes are identical in their shape. As both cubes sink in water, they are heavier than water.
7.
If he pushes the glass in inclined inverted position, say, at 45° angle than water enters as air can escape out
Coffee, mercury etc, is a liquid that have definite volume but no
easily. 8.
definite shape. They also does not allow light to pass through them.
Volumes of P and Q are unequal but masses are equal.
PREVIOUS CONTEST QUESTIONS 2.
Matter Solid
Liquid
Gas
Paper
Milk
Oxygen
Coffee
Syrup
Wind
1.
(B) One of the assumption of kinetic molecular theory is collisions are short in duration.
2.
(C) Kinetic energy of the molecular motion appears as temperature since it varies with change in temperature.
3.
(C) Triple point of water is 273. 16 K. At this temperature all the three
Powder Mercury
3.
(D) P is a vapour and its particles are far apart and Q is a liquid which has particles not so closely packed like a solid.
4.
(a) (b)
physical states exist in the given conditions.
Oil does not flow inside the flask because air is present in it. Raj has to fix a straw to enable the air out of the oil.
4.
called vanderwaals forces.
Straw
(c)
(A) Intermolecular forces are also
5.
(B) They are perfectly elastic without losing or gaining energy during collisions.
6.
(C) Solids have a regular and repeated
Raj can enable the oil to flow into the flask easily by removing the
molecular pattern because of close packing of molecules. But in
air using the straw as an out let.
liquids and gases the arrangement of molecular pattern it is irregular.
1. States of Matter
5
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7.
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(D) Fog is a solid dispersed in gas and
BRAIN NURTURES
hence is called as aerosol. 8.
9.
10.
(A)
(B)
(B)
1.
When water particles condense on air and dust, it forms a mist which
change in the physical states of water from liquid to solid or gas. Even the
acts as a screen (opaque) causing poor visibility.
variation in pressure also leads to the change in state.
One of the important assumptions of Kinetic theory of gases is that
For example: On applying pressure on a piece of ice, freezing point of ice
they have same average kinetic energy.
decreases leads to melting of ice i.e., change of state.
By lowering the temperature and
2.
the boiling point. Therefore, impure water has higher boiling point than pure
liquefaction of gases is possible.
water. On boiling of equal amounts of two samples the sample that needs
(C)
Normal temperature of human body is 37 °C.
12.
(C)
When the vapour pressure of a
more heat to boil it is an impure sample. 3.
liquid is equal to its atmospheric pressure, it boils. (A)
4.
Ice, a solid is converted to water,
used wrought iron. 5.
(D) By increasing the, temperature of a body, means there is an increase
On sprinkling brine solution, a soluble impurities a decrease in melting point of ice occurs. Hence, ice piled on roads by melting it.
in thermal energy.
1. States of Matter
Copper contracts on freezing but wrought iron expands on freezing and takes the exact shape of the mould. Hence, perfect moulds are prepared,
(D) Thermal energy of a body is due to the kinetic energy of its molecules and hence it is same.
15.
Heat is absorbed by the bulk of the material and causes increase in potential energy.
(a liquid) by gaining heat. 14.
Impurities in a liquid cause increase in
applying low pressures below the critical temperature of a gas, then 11.
13.
Variation in temperature leads to
6
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Symbols, Formulae Natural Phenomenon Force and Pressure and Equations SOLUTIONS 5.
B ASIC P RACT ICE
(A) A formula tells us about the number of atoms present in a molecule.
F IL L IN T HE B L ANKS 4.
In Ba(HO3)2 , HCO3 is an ion and is called bicarbonate ion.
6.
13.
2 NaOH + H2 SO4 → Na 2SO4 + 2H 2O
7.
14.
For 4 g of hydrogen i.e, for 2H 2 , 16 × 2 = 32 g of oxygen is needed.
15.
HCl = 1 + 35.5 = 36.5
a short form by the formula.
of the products. 8.
(C) Sodium oxalate formula is Na2C2O4.
9.
(D) (i)
MULTIPLE CHOICE QUESTIONS (B)
(C) A balanced chemical equation supports the law of conservation of mass as the total mass of the reactants is equal to the total mass
F U RT H ER P RACT ICE
1.
(A) A compound can be represented in
Symbols of lead and mercury are
bivalent (ii) Ammonium NH4+
Pb and Hg respectively. 2.
(D) A symbol of an element does not convey the information about its atomic number, nor atomic weight
(iii) Sodium
(C)
The molecular weights of H2O, H2S, CO2 and SO2 are 18, 34, 44
monovalent
and 64 respectively. Hence, the increasing order of molecular weights is H2O < H2S < CO2 < SO2. 4.
(C)
Atomicity of an element tells us about the number of atoms in a molecule.
2. Symbols, Formulae and Equations
monovalent Na
monovalent (iv) Bicarbonate ion HCO3
nor mass number. 3.
Sulphite ion SO32
7
10.
(A) Soda ash is the trivial name of sodium carbonate (Na2CO3).
11.
(A)
CrO24 and Cr2O72 are the formulae of chromate and dichromate ions respectively.
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(D) Sulphate ion is bivalent and others
respectively. The chlorate and
are trivalent. 13. 14.
15.
(A) (A)
(C)
nitrate have formula, MClO3 and MNO3 respectively.
Inert gases are not chemically active and their valency is zero.
In the given options, M2SO4 and MHCO3 are correct.
From the formula of chromic acid H2CrO4 . The valency of chromate
5. (A,B,C) From the given formula valency
ion is two and the formula of divalent metal chromate is MCrO4.
of the metal can be deduced as 3 and its formulae of oxide, nitride,
Pyrophosphate ion radical valency
bicarbonate and chlorate are A2O3, AN and A(HCO 3 ) 3 , A(ClO 2 ) 3
is 4 and formula of sodium pyrophosphate is Na4P2O7.
respectively.
ASSERTION AND REASONING
MULTIPLE ANSWER QUESTIONS 1. (A, B)
1.
Among the four, hydrogen phosphate (HPO42) and sulphate
is called ferrous ion and it is bivalent i.e., Fe+2.
ions (SO 4 2 ) are bivalent. Perchlorate (ClO4) is univalent while nitride (N3) is trivalent. 2.(A,B,C)
2.
products formed, balancing of a chemical reaction is important. It also tells about the energy changes takes place. But energy changes
of combining metallic radical but not M2X.
solely help to study a chemical reaction.
Equations (C) and (D) are not balanced as the atoms of different elements on reactants side and
3.
correct formula is CaSO4.
SiCl4 + 2H 2 O → SiO2 + 4 HCl
4.
2NaOH + H2O2 → Na2O2 → Na2O2 + 2H2O
Since the metal is univalent, its
(A) Hydrogen atom has only one proton but no neutrons and its mass number is one. Hence, mass number is e q u a l t o a t o m i c
sulphate and hydrogen carbonate have formulae M2SO4 and MHCO3 2. Symbols, Formulae and Equations
(D) Calcium sulphate is a compound formed by combination of bivalent calcium and sulphate ions and its
products side are not equal. Equations (A) and (B) are balanced.
4.(A,D)
(B) To study the chemical reactions it is needed to know the amount of reactants required and the
Metals can have valencies either 1, 2 or 3. Valency of a halide is one and it can form MX, MX2 and MX3 and so on depending on the valency
3. (A,B)
(A) Iron atoms loses two electrons and carries two positive charges and it
number. 8
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5.
(B)
Class – VIII / Chemistry/ Solutions
Atomic weights of carbon and
BRAIN NURTURES
oxygen are constant and they combine in a fixed ratio by their weights 12 : 32 = 3 : 8 in CO2.
1.
Valency of oxygen is always two and valency of nitrogen will be five in N2O5.
2.
Fluorine has valency one. So, valency of sulphur is two, four and six in SF2, SF4 and SF6 respectively.
3.
From the formula of peroxide valency of Radium is 2 and its formulae for the compounds are
PARAGRAPH QUESTIONS (i)
(A)
Since the salt of oxyacid of metal has one sulphur atom and four oxygen atoms its valency is one.
(ii)
(A)
Its formula of base is MOH.
(iii)
(A)
The oxyacid of salt is H2SO4.
(A)
(B)
The possible and accepted symbols are Sw, Sh, St and Sa as the first and second or subsequent letters in english for her
(C)
(A) Calcium carbide, (B) Calcium hydride, (C) Aluminium nitride, (D)
(D)
4.
→ 6Cu + SO2. Cu2S + 2Cu2O ⎯⎯
5.
Since the binary salt of nitride of the
(E)
4.
5.
"
+
From the reaction,
Balanced equation is:
→ 2Na2CrO4 + 2Cr(OH)3 + 3Na2O2 ⎯⎯ 2H2O + 2NaOH and number of atoms of different elements on both sides are equal.
MS
2. Symbols, Formulae and Equations
Ra C
Na2S2O3 + 2HCl → 2NaCl + SO2 + H2O+ S
is M2S as the valency of sulphide is two. 2
Ra (HSO")
4="+
metal has 3 metal atoms, valency of the metal is one and its formula of sulphide
1 M
!
Ra (HSO4 )2
potassium phosphite respectively. Δ CaCO 3(s) ⎯⎯ → CaO (s ) + CO 2(g ) ↑
Ra (PO ")
Ra 3 ( PO4 )2
letter must be always a small letter.
3.
Ra S
Ra 2S2 (or) RaS
name. Secondly, the first letter S must be capital letter while the subsequent 2.
1
Ra ( MnO4 )2
CONCEPTUAL QUESTIONS 1.
Ra 2 (MnO4 )
9
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!
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Transformation of Substances SOLUTIONS 3.
MULTIPLE CHOICE QUESTIONS 1.
water to steam is a physical change only as the composition remains
(D) Chemical change always produces a new substance. Though some chemical and physical changes are
same only there is a change in state.
irreversible. For example (i)
4.
Breaking of a glass is an irreversible physical change.
more reactants participate in a chemical reaction.
nitrogen and hydrogen can be reversed under certain
5.
conditions. Hence, it is an reversible chemical change. (B)
(B) In physical change normally some specific property of a substance like melting point, physical state etc., alters but no change in composition.
Water soluble substances dissolve in it and form solutions and can be obtained back by evaporation.
6.
(D) This compound nitric oxide is formed by chemical combination of two elements nitrogen and
Reaction of zinc metal with dilute sulphuric acid forms zinc sulphate and hydrogen gas.
oxygen. N2 + O2 → 2NO
Hence it is a chemical change. 7.
Similarly, burning of coal produces carbon dioxide and water vapour while during photosynthesis
(D) Chemical combination involves combination of two or more elements or compounds.
starch and carbon dioxide are formed.
3. Transformation of Substances
(D) A chemical change is associated with energy changes, formation new substances and usually two or
(ii) Preparation of ammonia from
2.
(A) The conversion of ice to water and
For example H 2 + C l2 → 2HC l This is a element-element combination reaction. 10
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oxygen hence it is a decomposition
CaO + H2 O → Ca(OH)2
reaction. Due to spliting of a single compound.
This is a compound-compound reaction. 8.
(B)
12.
This is an example of double
takes place.
13.
Reaction with absorption of energy is called an endothermic reaction.
14.
is called an exothermic reaction.
reddish brown gas hence the reaction is
In the reaction (ii) on burning of magnesium wire magnesium oxide
2NO + O2 → 2NO 2
is formed by release of energy in the form of heat and light.
15.
Hence it is an exothermic reaction.
(B) Decomposition of a single compound into new compounds is possible. For example, calcium carbonate on strong heating
In this reaction a compound on heating decompose to give two new compounds, Cuprous oxide
decomposes to give calcium oxide and carbon dioxide.
and water.
Combination of two elements is possible. For example.
Reaction between calcium oxide and water gives calcium hydroxide
O2 + 2 H2 → 2H2O
and it is an example of combination reaction. Because of formation of
16.
(A) Water decomposes hydrogen and oxygen.
17.
(C) Law of conservation of mass states that in a chemical reaction, the
single compound. Mercuric oxide on strong heating decomposes to form mercury and 3. Transformation of Substances
(A) Nitric oxide, NO combines with oxygen to form nitrogen dioxide NO 2 . Nitrogen dioxide gas is
Reaction with the release of energy
(C)
(B) Oxygen oxidises aluminium to aluminium oxide.
oxidising agent as it undergoes reduction.
carbon dioxide, hence it is an endothermic reaction.
11.
new
reducing agent as it undergoes oxidation while oxgyen acts as a
bicarbonate needs energy to form sodium carbonate, water and
(B)
two
Hence aluminium acts as a
In the reaction (i) Sodium
10.
reaction
of radicals in lead nitrate and sodium iodide.
formation of two new substances. i.e., a mutual exchange of radicals (B)
this
substances lead iodide and sodium nitrate are formed by interchange
decomposition reaction because an interchange of radicals lead to the
9.
(D) In
11
to
give
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