Superior Lalazar Public School and College Thana
www.slpsorg.com 0932-442385 email. 0917351@rgu.ac.uk
Solved Chemistry 9th 2013 paper Swat Board.
Section B (Marks 32)
Q. 2 Answer any eight parts. Each part carries 4 marks
(i)
How many moles of CO2 are present in 60 gram of CO2?
Ans.
Given data:
Molecular weight of CO2 = 12 + 32 = 44 g
Given weight of CO2 = 60 g
Formula used:
𝑮𝒊𝒗𝒆𝒏 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒔𝒖𝒃𝒔𝒕𝒂𝒏𝒄𝒆
Moles =
𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
Solution:
𝟔𝟎
Moles = = 1.36
𝟒𝟒
So 60 gram CO2 contain 1.36 moles CO2
(ii)
What is atomic number of an element? How it differ
from the mass number?
Atomic Number
Mass Number.
1. Definition:
1.Definition. The sum of the
The number of protons in the
number of protons and neutrons
nucleus or The number of
present in the nucleus of an atom
electrons present around the
is called mass number.
nucleus of neutral atom is called
its atomic number.
2.Representation. Mass number
2.Representation:
is represented by ‘A’
Atomic number is represented by
capital letter “Z”.
3.Mathematically
3.Mathematically
Mass number (A) = Number of
Atomic number = Number of
protons (Z) + number of
protons
neutrons
OR
Z = A - neutrons
4. It does not determine the
identity of an element but
4.It determines the identity of an isotopes
element
5. Examples:
5. Examples:
The mass number of carbon is
The atomic number of carbon is
12.The mass number of oxygen
6.The atomic number of oxygen is 16
is 8
(iii)
Give reasons to prove that atom is a neutral particle
Ans. As the number of electrons (negative particles) in atom is
always equal to the number of protons (positive particles), therefore
atom is a neutral particle because cancel the effects of each other. In
other words the charge on electron is -1.6x10-19 and proton is
+1.6x10-19 so the resultant charge will be zero (-1.6x10-19+1.6x1019 = 0)
(iv)
Describe the uses of isotopes?
Ans. Uses of Isotopes: Isotopes are mainly used in chemical,
agricultural and medical research and for diagnosing and
treatment of diseases. For instance:
 1. Iodine- 131 is used in the treatment of thyroid cancer.
 2. Radium irradiation and cobalt-60 are used in the treatment
of cancer and for diagnosis of tumours.
 3. Deuterium, heavy carbon {C-13), heavy nitrogen (N-I 5) and
heavy oxygen (O-18) are being, used as tracer elements in
biochemical and physio-chemical research.
 4. Sodium-24 is used for the identification of blood circulation
problems in patients.
(v)
What do you mean of electron affinity of an element?
Discuss its variation in periodic table?
Ans Electron Affinity: The amount of energy released when
electron is added to isolated gaseous atom to form negative ion is
called electron affinity.
Electron affinity means love for electron so when atom accepts
electron it releases energy to form anion
Electron affinity is measured in KJ/mol
Example Cl + 1e -- Cl-1 E.A = -349KJ/mol
Variation of electron affinity in periodic table
 In periods, the electron affinity increases from left to right
because nuclear charge increases and atomic radium decreases
 In groups, the electron affinity decreases from top to bottom
because atomic radius and shielding effect increased.
(vi)
Give electronic configuration of Na and Cl.
Ans
Na (Z= 11) 1s2 2s2 2p6 3s1 so K = 2 L= 8 M= 1
Cl (Z= 17) 1s2 2s2 2p6 3s2 3p5 so K = 2 L= 8 M= 7
(vii)
What is the difference between polar and non polar
covalent bond? Explain with examples.
Ans.
Polar Covalent bond
Non Polar covalent bond:
1.Definition: The type of
covalent bond in which the
shared pair electrons are
attracted unequally by both
bonded atom is called polar
covalent bond
1.Definition: The type of
covalent bond in which the
shared pair electrons are
attracted equally by both
bonded atom is called non polar
covalent bond
2. formed between two different
atoms having different
electronegativity
2. Formed between two same
atoms having same
electronegativity
3 partial positive on low
electronegative atoms and
partial negative charge on high
electronegative bonded atom.
3. Molecule remains neutral. .
Examples when a Covalent bond
is formed between H and Cl , it
is polar in nature because Cl is
more electronegative than H
atom . Due to this reason a
partial -ve charge appeared on Cl
atom and an equal +ve charge
Examples: The bond between two
hydrogen is non polar because
shared pair electrons are
attracted equally by both atoms
H-H
Same with Cl2, O2
on H atom
Same with HF, NH3
(viii)
What is hydrogen bonding? Explain
Hydrogen bond or bonding:
Definition: The force of attraction between hydrogen atom of one
polar molecule and high electronegative atom like oxygen, nitrogen
or fluorine of another polar molecule is called hydrogen bond or
bonding.
Explanation: hydrogen bond is formed when hydrogen atom is
covalently bonded to only oxygen, nitrogen or fluorine. These high
electronegative atoms (O, N or F) must have lone pair electrons.
The hydrogen bond formed because lone pair of O, N or F of one
polar molecule attracts the partial positive hydrogen of another
polar molecule. Hydrogen bond is not a chemical bond due to which
weaker than covalent bond but stronger than dipole-dipole
interaction. It is represented by dotted lines (……)
Example1: hydrogen bond is present in water molecules due to
which water is liquid at room temperature.
Hydrogen bond is also present in NH3 and HF molecules.
(ix)
Write properties of ionic compound.
Ans. Ionic compounds are those compounds which contain ionic bond.
The main properties of ionic compounds are given below
1. Ionic compounds are solid at room temperature
2. Ionic compounds are hard and brittle
3. Ionic compounds have high melting and boiling point
4. Ionic compounds are soluble in water and other polar solvents
5. Ionic compounds are good conductor of electricity at molten or
solution state
6. Ionic compounds reactions are very fast in solution
(x)
What is electroplating? Write its significances.
Electroplating:
Definition: The process in which a thin layer of one metal is
deposited on another metal by electrolysis is called electroplating.
Examples: zinc plating, chrome plating, silver plating and tin
plating etc
Purpose of electroplating or significances:
 Protection of inner metal from atmospheric effect like corrosion
 Repairing of broken parts of machinery by electroplating
 Decoration of metal by noble metal like silver, gold etc
(xi)
What are the uses of magnesium?
 It is used for making alloys
 It is used for the preparation of magnesium sulphate which is
then used in paper, textile and soap etc
 It is used for the preparation of magnesium oxide which is
then used to make refractory bricks for furnace lining.
Section C
Q. 3 (a) What is mixture? Describe types of mixture
Mixture.
The physical combination of two or more substances is called mixture
OR When two or more substances combine physically in which each
substance retains their original chemical properties is called mixture.
Examples.
Salt solution, sugar solution, air, soil etc.
Types of mixture. Mixtures are two types
1. Homogeneous mixture.
The type of mixture which has uniform composition throughout their
mass is called homogeneous mixture.
Examples.
Salt solution is homogeneous mixture because there are no clear
boundaries between salt and water in salt solution. Similarly sugar
solution, ethyl alcohol solution, air etc are examples of homogeneous
mixture
2. Hetrogeneous mixture.
The type of mixture in which all components do not have uniform
composition throughout their mass is called hetrogeneous mixture.
Examples. Petrol mixed with water is heterogeneous mixture because
there are clear boundaries between petrol and water. Similarly concrete
is heterogeneous mixture of sand, rock and cement.
Q. 3 (b) Describe Neil Bohrs atomic theory in detail.
Ans. Neil Bohr’s atomic theory.
In order to remove the defects of Rutherford atomic model that why
electrons do not fall in the nucleus, Neil Bohr’s in 1913 gave his
atomic model and the main points are given below:
1. Electrons revolve around the nucleus in a fixed circular path called
orbit or energy level. Each orbit has a fixed size, shape and energy.
2. Electron does not absorb or emit energy when revolves around the
nucleus in a fixed orbit.
3. Electron only absorbs or emits energy when jumps from one orbit to
another and the energy absorbed or released is not continuous but
discontinuous in the form of quantum (photon).
4. Electron releases energy when jumps from higher orbit to lower orbit
but absorbs energy when jumps from lower orbit to higher orbit.
5. The energy absorbed or released is always equal to the difference of
the energy of the two orbits. ∆E = E2-E1 = hⱱ
Where ‘h’ is planks constant and ‘ⱱ’ is frequency of radiation.
6. Electron only revolves around the nucleus on those orbits for which
the angular momentum (mvr) is equal to ‘nh/2π’.
mvr = nh/2π
where ‘m’ is mass of electron, ‘v, is velocity, ‘r’ is radius of orbit, ‘n’ is
any natural number (1,2,3-----) and ‘h’ is a plank constant
(6.6262x 10-34J)
Q. 4 (a) What do you understand by the periodicity of properties?
Discuss the periodicity of the atomic size of the element in periodic
table.
Ans. The repetition of a property of the element in periodic table after a
certain interval is called periodicity of properties.
When elements are arranged according to their increasing atomic
number, elements with similar properties fall within the same group
which means properties of given elements are repeated.
 In period from left to right, the atomic sizes decrease because
nuclear attraction for valence electron increases.
 In group from top to bottom, the atomic size increases because
shielding effects increase as new shells are added.
Q. 4 (b) Define covalent bond and explain its types in detail.
Covalent Bond:
Definition: A chemical bond formed between atoms by the mutual
sharing of electrons is called covalent bond.
REPRESENTATION:
Covalent bond between two atoms is represented by a short line
Example: Two hydrogen atoms when combines by mutual sharing it
forms hydrogen molecules H-H (H2)
Types of covalent bond: There are three types of covalent bond
depending upon the number of shared pair electrons between bonded
atoms.
1. Single covalent bond:
Definition: A covalent bond formed by mutual sharing of one pair of
electrons is called single covalent bond OR The covalent bond in
which each bonding atom share only one electron is called single
covalent bond
Representation: A single bond is represented by a single dash (-)
between the two atoms.
Example, The two hydrogen atoms in H2 molecules are bonded by a
single bond, because two H atoms share only one pair of electrons.
2. Double covalent bond:
Definition: A covalent bond formed by mutual sharing of two pair of
electrons is called double covalent bond OR The covalent bond in
which each bonding atom share only two electrons is called double
covalent bond
Representation: Double covalent bond is represented by two dashes
(=) between the two atoms.
Example, Two oxygen atoms combine together to form a molecule of
oxygen by mutual sharing of two pair of electrons.
3. Triple covalent bond:
Definition: A covalent bond formed by mutual sharing of three pair of
electrons is called triple covalent bond OR The covalent bond in which
each bonding atom share only three electrons is called triple covalent
bond
Representation: Triple covalent bond is represented by three dashes (≡)
between the two atoms.
Example, Two nitrogen atoms share three pair of electrons to form a
molecule of Nitrogen (N2).
Q. 5 (a) Write a detail note on Daniel Cell.
Daniel Cell.
Definition: The galvanic cell in which electric current is produced
with the help of Zn-Cu redox reaction is called Daniel cell.
Explanation:
1. The zinc sulphate solution is taken in one beaker and zinc
rod is placed in that solution
2. The copper sulphate solution is taken in another beaker and
copper rod is placed in that solution
3. The two solution are separated by U-shape tube called
saltbridge. The tube is filled with electrolyte KCl.
4. The two metal rods are connected with voltmeter with the
help of electric wire to measure electric current
5. When the circuit is completed, Zn oxidizes to Zn+2 and
gives electron to the electrode
6. The electrons travel toward copper electrode with the help of
external wire where copper ions (Cu+2) of solution gain
electrons and reduced to Cu.
7. The electricity is produced by traveling of electron
Anodic half cell reaction:
Zn ------------- Zn+2 + 2e
Cathodic half cell reaction:
Cu+2 + 2e ---- Cu
Net reaction
Zn + Cu+2 ------------- Zn+2 + Cu
Q 5 (b) Write the physical properties of sodium.
i. it is soft metal and can be cut with a knife
ii. The melting point is 97.6C and boiling point is 880C
iii. it is grayish white metal
iv. Its density is 0.971 g/cm3 and lighter than water so floats
on the surface of water
iv. Good conductor of electricity due to motion of free valence
electron
Q 6 (a) State Charles Law. How mathematically it is represented?
Statement
The volume of a given mass of a gas is directly proportional to
absolute temperature at constant pressure
Mathematical representation
Let the volume of a gas at ‘T’ Kelvin is ‘V’
Then according to Charles’s law
VαT
To convert proportionality into equality a constant is introduced
V = (constant) T
𝑽
𝑻
= constant
Second statement:
By using above equation ,Charles’s law can also be stated as:
The ratio of volume to absolute temperature of a gas at constant
pressure is always constant
Similarly
At T1
𝑽𝟏
𝑻𝟏
= constant ---------------(1)
At T2
𝑽𝟐
𝑻𝟐
= constant ---------------(2)
Comparing equation 1 and 2
𝑽𝟏
𝑻𝟏
=
𝑽𝟐
𝑻𝟐
Q 6 (b) Define solubility. How pressure affect the solubility of gases?
Solubility: The number of grams of the solute necessary to saturate
100gm of the solvent at particular temperature is called solubility.
OR
The maximum amount of solute in grams required to saturate 100
grams of solvent at given temperature is called solubility.
EFFECT OF PRESSURE
The solubility of solids and liquids are not affected by pressure
because solids and liquids are incompressible. The effect of pressure is
observed only in the case of gases.
The solubility of gases in liquid is directly proportional to pressure
above the liquid i.e the solubility of gases increase with increase in
pressure
For example carbon dioxide is filled in cold drink bottles (such as
coca cola, Pepsi 7up etc.)under high pressure because to increase
solubility of carbon dioxide in cold drinks.
Q 4 (b) What do you understand by shielding effect? How it
effect the electron affinity of the element in periodic table?
Ans. Shielding effect: The reduction in the force of nuclear
attraction on the outer electrons due to inner electrons is called
shielding effects or screening effect. OR the reduction in force
of attraction by the shells present between nucleus and
valence electrons is called shielding effect.
In shielding effect, the core electrons block valence electrons
from the nuclear attraction.
The shielding effects remain constant from left to right in
periods but nuclear charge increases due to which electron
affinity will increase from left to right in periods. The
shielding effects increase from top to bottom in group so
electron affinity decreases from top to bottom in group as
inverse relationship presents between shielding effect and
electron affinity.