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Superior Lalazar Public School and College Thana www.slpsorg.com
0932-442385 email. 0917351@rgu.ac.uk
Solved Chemistry 9 th
2013 paper Malakand Board.
Section B (Marks 32)
Q. 2 Answer any eight parts. Each part carries 4 marks
(i) Define the atomic number of an element. Give two examples.
Atomic Number
Definition:
The number of protons in the nucleus or The number of electrons present around the nucleus of neutral atom is called its atomic number.
Representation:
Atomic number is represented by capital letter “Z”.
Mathematically
Atomic number = Number of protons
OR
Z = A - neutrons
It determines the identity of an element
Examples:
The atomic number of carbon is 6.The atomic number of oxygen is 8
(ii) State the shortcoming of Rutherford atomic model.
Drawbacks or shortcoming or defects in
Rutherford atomic model.
The following defects were observed in Rutherford atomic model:
 In Rutherford atomic model, electron is a charged particle revolves around the nucleus in a circular path but according to classical electromagnetic theory the charged particles lose energy continuously. Therefore electrons should lose energy continuously and ultimately fall in the nucleus but it does not happen.
 If the revolving electrons radiate or emit energy continuously, then the atomic spectrum must be continuous instead of line spectrum.
(iii) How will you differentiate the modern periodic law from that of
Mendeleev’s periodic law?
Modern Periodic law Mendeleev’s periodic law
1.Statement. The properties of elements are the periodic function
1.Statement. The properties of elements are the periodic function of their atomic number
2. The elements arranged on the of their atomic weight
2. The elements arranged on the

2 basis of their increasing atomic number
3. position of isotopes is clear basis of their increasing atomic weight
3. position of isotopes is not clear
(iv) What do you understand by the term shielding effect?
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 because the number of shells remains constant.
 The shielding effects increase from top to bottom in group because the number of shells increases.
(v) State octet rule.
Octet Rule: When atoms complete their outer remaining shell by eight electrons through loss, gains or sharing, the rule followed by atoms is called octet Rule.
Example. Chlorine(Cl) follows octet rule because needs one electron to complete outer shell by eight.
(vi) Write down the characteristics 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
(vii) In a hot summer day when there is sweat on the body of a person one feels cool under fast moving fan. Explain why.
In a hot summer day a person feels cool under fast moving fan if there is sweat on the body because fast moving fan increases the rate

3 of evaporation of sweat from the body. During evaporation, sweat on the body absorbs heat from body due to which body temperature falls and sensation of cool are felt.
(viii) Explain the difference between solution and suspension.
Solution:
1.Definition: The homogeneous mixture of two or more substances is called solution
2. its composition is uniform throughout
3. There are no visible boundaries between components of solution.
4. The particles of solution can pass through filter paper.
5. The particles of solution will not settle down at bottom of container if left for long time.
Example. Sugar solution, salt solution etc
Suspension:
1.Definition: A heterogeneous mixture of two or more substances having none uniform composition throughout and contains insoluble particles in solvent is called suspension. 2. Its composition is not uniform throughout
3. Solute particles can be seen with naked eye.
4. The particles of suspension cannot pass through filter paper.
5. The particles of suspension settle down at bottom if left for long time.
Examples, 1) mixture of chalk
2) mud in water
(ix) Explain various types of solid with examples.
Solids are two types depending upon the arrangement of particles
1) Crystalline solids 2) Amorphous solids
CRYSTALLINE SOLIDS:
Definition: The solids in which the particles (Atoms, ions or molecule) are arranged in a regular pattern in three dimensions and have definite shape are called crystalline solids.
Explanation: Crystalline solids have the following fundamentals properties.
1. They have characteristic geometrical shape.
2. Planes of a crystal intersect at particular angles.

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3. They have sharp melting and boiling points.
Examples: Copper Sulphate (CuSO4), NiSO4, Diamond, Graphite,
NaCl, etc
AMORPHOUS SOLIDS:
Definition: Solids in which particles are not orderly arranged and don’t have a definite geometrical shape are called Amorphous Solids.
Explanation: Amorphous solids have the following properties
1. In these solids particles are randomly arranged in three dimensions.
2. They don’t have sharp melting points.
3. Amorphous solids are formed due to sudden cooling of liquid.
4. Amorphous solids melt over a wide range of temperature
Examples: Coal, Coke, Glass, Plastic, rubber etc
(x) Define oxidation and reduction. Give examples.
Oxidation: The addition of oxygen or removal of hydrogen or loss of electrons or increase in oxidation state during a reaction is called oxidation.
Examples:
REDUCTION: The addition of hydrogen or removal of oxygen or gain of electrons or decrease in oxidation state during a reaction is called reduction.
Examples

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(xi) Describe 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
Section C
Q 3 (i) Differentiate by given examples between element, compound and mixture.
Element
1.pure substance
Compound
1.The type of
Mixture
1.The physical

6 which contains only one kind of atoms is called element.
2.Element is a pure substance
3. Cannot be broken down into simpler substances by ordinary chemical or physical methods.
4.The fundamental unit of an element is the atom.
5.Elements are represented by chemical symbols.
Examples.
Copper (Cu), Iron (Fe),
Nitrogen (N),
Sulphur (S) etc are elements. substance which is made from the chemical combination of two or more elements by fixed ratio of mass is called compound
2.It is pure substance
3.Its composition is fixed
4.It cannot be separated by physical method
5. Substances making the compounds lose their original properties
6. represented by formula combination of two or more substances is called mixture
2.It is an impure substance
3.Its composition is not fixed
4.It can be separated by physical method
5.Substances making the mixture retain their original properties
Q 3 (ii) What is the mass of 5 moles of ice?( H= 1amu, O= 16 amu)
Ans
Molecular weight of ice(water) H2O = 2+ 16 = 18
Moles =
𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒔𝒖𝒃𝒔𝒕𝒂𝒏𝒄𝒆 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
So weight of ice = moles X molecular weight. 5X 18 = 90 gram
Q. 4 (i) Explain Charles law.
Ans. Charles law
Introduction

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This law was given by Charles in 1780. He gave a quantitative relation between volume and absolute temperature of a gas at constant pressure.
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
V α T
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. 4 (ii) if 3 dm
3
of air is heated from 300K to 400K at constant pressure, then what is the volume of the gas at higher temperature.
Given Data:

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V1 = 3 dm 3 T1 = 300K T2= 400K
Required Data; V2= ?
Formula used:
𝑽𝟏
𝑻𝟏
=
𝑽𝟐
𝑻𝟐
( charles law)
Solution: V2 =
𝑽𝟏𝑻𝟐
𝑻𝟏
=
𝟑𝑿 𝟒𝟎𝟎
𝟑𝟎𝟎
= 4 dm 3
Q 4 (i) Define halogens. Which elements are included in halogens?
Halogens: Group VII elements are collectively called halogens (salt former)
There are five elements in 7 th group which are fluorine (F), chlorine(Cl), bromine(Br), iodine(I) and astatine(At).
Characteristics of halogens:
 All the elements of group VII-A contain seven electrons in their outermost shell.
 Generally they are present in (-1) oxidation state.
 Elements of group VII-A are non-metals.
 They are highly electronegative elements.
 They exist as diatomic molecule. For example F2, Cl2, Br2, I2,
At2
Q 4 (ii) Write the chemical properties of halogens with hydrogen and metals
1.
Reaction of hydrogen: Halogens when react with hydrogen it form hydrogen halides.
H
2
+ F
2
--- 2HF
H
2
+ Cl
2
--- 2HCl
H
2
+ Br
2
--- 2HBr
H
2
+ I
2
--- 2HI
2.
Reaction with metals; Halogens when react with metals it form halides
Cu + Br
2
 CuBr
2
2Na + F
2
--- 2NaF
Fe + Cl
2
--- FeCl
2
2K + I
2
--- 2KI
Q. 6 (i) Define covalent bond and explain its types in detail.
Covalent Bond:

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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 (H
2
)
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 H
2
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:

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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 (N
2
).
Q. 6 (ii) What is vapour pressure? What are the factors which affects vapour pressure?
Vapour pressure:
Pressure exerted by the vapour of a liquid at equilibrium is called
Vapour Pressure of that liquid. OR
Pressure exerted by the vapours of a liquid when rate of evaporation becomes equal to the rate of condensation is called Vapour Pressure.
Factors affecting vapour pressure: a.
The nature of liquid: The vapour pressure depends upon the strength of intermolecular forces, stronger the intermolecular forces smaller will be the vapour pressure. b.
Temperature. The vapour pressure of liquid increased with increased in temperature.