9th Chemistry Notes - Test Yourself (Malik Xufyan)

9th Chemistry Notes [Test Yourself]

Test Yourself [9th
Chemistry Notes] Malik Xufyan
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www.onlychemistrydiscusson.blogspot.com
Test YourSelf 1.1
1. In which branch of chemistry behaviour of gases and liquids is studied?
Ans. The behaviour of gases and liquids is studied in physical chemistry
2. Define biochemistry?
Ans. It is the branch of chemistry in which we study the structure, composition, and chemical
reactions of substances found in living organisms.
3. Which branch of chemistry deals with preparation of paints and paper?
Ans .Industrial chemistry deals with preparation of paints and paper.
4. In which branch of chemistry the metabolic processes of carbohydrates and proteins
are studied?
Ans .The metabolic processes of carbohydrates and proteins are studied in biochemistry
5. Which branch of chemistry deals with atomic energy and its uses in daily life?
Ans .Nuclear chemistry deals with atomic energy and its uses in daily life.
6. Which branch of chemistry deals with the structure and properties of naturally
occurring molecules?
Ans: Organic chemistry deals with the structure and properties of naturally occurring molecules.
Test Yourself 1.2
1. Can you identify mixture, element or compound out of the following: Coca cola,
petroleum, sugar, table salt, blood, gun powder, urine, aluminium, silicon, tin, lime
and ice cream?
Ans.
Element Aluminium, silicon, tin
Compound Sugar, Table salt, Lime
Mixture Coca cola, Petroleum, Blood, Gun
powder, Urine, Ice cream
2. How can you justify that air is a homogenous mixture. Identify substances present in
it?
Ans. Air is a homogenous mixture because it has uniform composition throughout. Air is a
mixture of nitrogen, oxygen, carbon dioxide, noble gases and water vapours.
3. Name the elements represented by the following symbols: Hg, Au, Fe, Ni, Co, W, Sn,
Na, Ba, Br, Bi.
Ans.
Symbol Name
Hg Mercury
Au Gold
Fe Iron
Ni Nickel
Co Cobalt
W Tungsten

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Sn Tin
Na Sodium
Ba Barium
Br Bromine
Bi Bismith
4. Name a solid, a liquid and a gaseous element that exists at the room temperature.
Ans.
Solid iron (Fe), Gold (Au), Silver (Ag)
Liquid Bromine (Br)
Gas Hydrogen (H2), Nitrogen (N2), oxygen (O2)
5. Which elements do the following compounds contain? Sugar, common salt, lime
water and chalk.?
Ans.
Compound Elements
Sugar Carbon, hydrogen, oxygen
Common Salt Sodium, Chlorine
Lime water Calcium, hydrogen, oxygen
Chalk calcium, carbon, oxygen
Test yourself 1.3
1. How many amu 1 g of a substance has?
Ans. 1g of a substance has amu equal to Avogadro’s number (6.02 x 1023
).
2. Is atomic mass unit a SI unit of an atomic mass?
Ans. Yes, atomic mass unit is a SI unit of an atomic mass.
3. What is the relationship between atomic number and atomic mass?
Ans. The relationship between atomic number (Z) and atomic mass (A) is given as:
Number of neutrons (n) = A - Z
4. Define relative atomic mass?
Ans. The relative atomic mass of an element is the average mass of the atoms of that element as
compared to 1/12th (one-twelfth) the mass of an atom of carbon- 12 isotope.
5. Why atomic mass of an atom is defined as relative atomic mass?
Ans. As we know that the mass of an atom is too small to be determined practically. However,
certain instruments enable us to determine the ratio of the atomic masses of various elements to
that of carbon-12 atoms. This ratio is known as the relative atomic mass of the element.
Test yourself 1.4
1. What is the relationship between empirical formula and formula unit?
Ans.
Emperical formula:
Empirical formula is the simplest whole number ratio of atoms present in a covalent compound.

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Example:
For example, the covalent compound silica (sand) has simplest ratio of 1:2 of silicon and oxygen
atoms respectively. Therefore, its empirical formula is SiO2.
Formula Unit
Formula unit is defined as the simplest whole number ratio of ions, as present in the ionic
compound. In other words, ionic compounds have only empirical formulae. Their molecular
formula and formula unit is same.
Example:
For example, formula unit of common salt consists of one Na+
and one CI–
ion and its empirical
formula is NaCl.
2. How can you differentiate between molecular formula and empirical formula?
Ans:
Sr# Molecular formula Empirical formula
1. Molecular formula shows the actual
number of atoms of each element
present in a molecule of that
compound.
Empirical formula is the simplest whole
number ratio of atoms present in a
compound.
2. Molecular formula is derived from
empirical formula by the following
relationship:
Molecular formula:
M.F = (Empirical formula) x n
Where n is 1,2,3 and so on
The empirical formula of a compound is
determined by knowing the percentage
composition of a compound.
3. Identify the following formulae as empirical or molecular formula: H2O2,CH4 ,C6H12O6
, C12H22O11,BaCO3, KBr?
Ans.
Empirical formula Molecular formula
BaCO3, KBr H2O2 , CH4 , C6H12O6 , C12H22O11
4. What is empirical formula of acetic acid (CH3COOH)?
Ans. Empirical formula of acetic acid is CH2O.
5. Calculate the formula masses of: Na2SO4 , ZnSO4 and CuCO3?
Ans.
To calculate formula mass of Na2SO4 :
Atomic mass of sodium = 23 amu
Atomic mass of sulphur = 32 amu
Atomic mass of oxygen = 16 amu
Formula mass of Na2SO4= 2(atomic mass of sodium atom) + (atomic mass of sulphur) +
4(atomic mass of oxygen)
= (2 x 23) + 32 + (4 x 16) = 46 + 32 + 64 = 142 amu
To calculate formula mass of ZnSO4:
Atomic mass of zinc = 65.38 amu
Atomic mass of sulphur = 32 amu

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Formula mass of ZnSO4
= (atomic mass of zinc) + (atomic mass of Sulphur) + 4(atomic mass of oxygen)
= 65.38 +32 + 4 x16 = 65.38 +32 + 64 = 161.38 amu
To calculate formula mass of CuCO3:
Atomic mass of copper = 63.5 amu
Atomic mass of carbon = 12 amu
Formula mass of CuCO3 = 63.5 + 12 + 3 x16 = 123.5 amu
Test yourself 1.5
1. Identify the followings as diatomic, triatomic or polyatomic molecules H2SO4, H2, CO2,
HCI, CO, C6H6, H2O
Ans.
Diatomic
molecule
Triatomic
molecule
Polyatomic
molecule
H2, HCI, CO CO2, H2O H2SO4 , C6H6
2. Identify among the followings as cation, anion, free radical, molecular ion or molecule:
Na+
, Br.
, N2
+
, N2, CI2, CO3
2-
, H-
, O2, O2-
Ans.
Cation Na+
, N2
+
Anion CO3
2-
,H-
,
O2-
Free radical Br .
Molecular
ion
N2
+
, CO3
2-
,
O2-
Molecule N2, CI2, , O2
Test yourself 1.6
1. Which term is used to represent the mass of 1 mole of molecules of a substance?
Ans.The term gram molecular mass is used to represent the mass of 1 mole of molecules of a
substance.
2. How many atoms are present in one gram atomic mass of a substance?
Ans. Avogadro’s number (6.02 x 1023
) of atoms are present in one gram atomic mass of a
substance.
3. Explain the relationship between mass and mole of a substance?
Ans. we can calculate the number of moles of a substance from the known mass of the substance
with the help of following equation:
No. of the moles =
4. Find out the mass of 3 moles of oxygen atoms?
Ans. Mass of 3 moles of oxygen atoms = no. of moles x molar mass of oxygen
= 3 x 16 = 48 g/mol

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5. How many molecules of water are present in half mole of water?
Ans. Solution:
Number of molecules present in 1 mole of water = 6.02 x 1023
Number of molecules present in half (1/2) mole of water = 6.02 x 1023
/2 = 3.01x1023
Test yourself 1.7
1. How many atoms of sodium are present in 3 moles of sodium and what is the mass of
it?
Ans.
1 mole of sodium contains atoms = 6.02 x 1023
Number of atoms of sodium in 3 moles = 3x 6.02 x 1023
= 18.06 x 1023
2. How many atoms are in 1 amu and 1 g of hydrogen (H)?
Ans.
Number of atoms in1 gram of hydrogen = 6.02 x 1023
The atomic mass of hydrogen = 1.008 g
Number of atoms in1 amu of hydrogen = 6.02 x 1023
/1.008
= 5.97 x 1023
3. How many atoms are present in 16 g of O and 8g of S?
Ans.
Atomic mass of oxygen = 16 g
Number of atoms in 16 g of O = 6.02 x 1023
Atomic mass of sulphur = 32 g
32 g of S contains atoms = 6.02 x 1023
1 g of S contains atoms = 6.02 x 1023
32 8 g of S contains atoms =
.
= 1.505x1023
4. Is the mass of 1 mole of O and 1 mole of S same?
Ans. No, mass of 1 mole of sulphur is two times the mass of 1 mole of oxygen.
5. What do you mean by 1 atom of C and 1 gram atom of C?
Ans. 1 atom of C means one single atom of carbon while 1 gram atom of C means 12 g of carbon
which contains 6.02 x 1023
number of carbon atoms.
6. If 16 g of oxygen contains 1 mole of oxygen atoms calculate the mass of one atom of
oxygen in grams?
Ans. Solution:
1 Mole (6.02 x 1023
atoms) of oxygen has mass = 16 g
1 atom has mass = 16 /6.02 x 1023
= 2.66 x 10-23
g
7. How many times is 1 mole of oxygen atom heavier than 1 mole of hydrogen atom?
Ans. Solution:
Mass of 1 mole of hydrogen = 1.008 g
Mass of 1 mole of oxygen = 16 g
So, we can say that mass of 1 mole of oxygen is 16 times heavier than mass of 1 mole of
hydrogen.

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8. Why does 10 g nitrogen gas contain the same number of molecules as 10 g of carbon
monoxide?
Ans. Molar mass of nitrogen gas and carbon monoxide is same i.e. 28g. That’s why 10 g
nitrogen gas contain the same number of molecules as 10 g of carbon monoxide

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Test Yourself 2.1
1. Do you know any element having no neutrons in its atoms?
Ans. Yes, the element having no neutrons in its atoms is hydrogen.
2. Who discovered an electron, a proton and a neutron?
Ans. Electron was discovered by Sir William Crooks. Proton was discovered by Goldstein
Neutron was discovered by Chadwick
3. How does electron differ from a neutron?
Ans. An electron has a negative charge on it. It revolves around the nucleus of an atom
Neutron has no charge on it. It is present in the nucleus of an atom.
4. Explain, how anode rays are formed from the gas present in the discharge tube?
Ans. Electrons from cathode are bombarded on molecules of gas present in discharge tube. These
molecules are ionized and form positive ions. These positive ions travel towards cathode in the
form of rays. These rays are called anode rays or canal rays.
Test Yourself 2.2
1. How was it proved that the whole mass of an atom is located at its centre?
Ans. Since most of the alpha particles in Rutherford’s experiment passed through the foil
undeflected, therefore most of the volume occupied by an atom is empty. The complete rebounce
of a few particles show that the nucleus is very dense and hard. These observations show that the
whole mass of an atom is located at its centre.
2. How was it shown that atomic nuclei are positively charged?
Ans. Rutherford bombarded alpha particles on gold foil. These are actually helium nuclei (He2
+
).
The deflection of a few alpha particles proved that there is a ‘center of positive charges’ in an
atom, which is called nucleus of an atom.
3. Name the particles which determine the mass of an atom?
Ans. The mass of an atom is due to the particles present in the nucleus of an atom. These
particles are protons and neutrons.
4. What is the classical theory of radiation? How does it differ from quantum theory?
Ans. According to Classical Theory of radiation, moving charged particles i.e. electron in an
atom release or emit energy continuously. According to Quantum Theory of Max Planck
revolving electron in an atom does not absorb or emit energy continuously. The energy of a
revolving electron is ‘quantized’ as it revolves only in orbits of fixed energy.
5. How can you prove that angular momentum is quantized?
Ans. Let angular momentum (mvr) of 1st orbit is mvr = nh/2π. By putting the values of h and π
Test Yourself 2.3
1. How many the maximum number of electrons that can be accommodated in a
psubshell?
Ans. Maximum number of electrons that can be accommodated in a p-subshell is six (6)
2. How many subshells are there in second shell?
Ans. second shell has two subshells i.e. s and p
3. Why does an electron first fill 2p orbital and then 3s orbital?

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Ans. Electrons are accommodated in different shells according to increasing energy. An electron
first fill 2p orbital and then 3s orbital because 2p orbital is lower in energy than 3s orbital.
4. If both K and L shells of an atom are completely filled; how many total number of
electrons are present in them?
Ans. If both K and L shells of an atom are completely filled then there are 10 total electrons
present in them.
5. How many electrons can be accommodated in M shell?
Ans. 2n2
formula tells us that M shell can accommodate 18 electrons in it.
6. What is the electronic configuration of a hydrogen atom?
Ans. The electronic configuration of a hydrogen atom is 1s1
7. What is atomic number of phosphorus? Write down its electronic configuration?
Ans. Atomic number of phosphorus is 15. Its electronic configuration is
1s2
, 2s2
, 2p6
, 3s2
, 3p3
8. If an element has atomic number 13 and atomic mass 27; how many electrons are there
in each atom of the element?
Ans. The number of electrons present is this atom is also 13.
9. How many electrons will be in M shell of an atom having atomic number 15.
Ans. Electronic configuration of an element having atomic number 15 is:
K shell = 2, L shell = 8, M shell = 5 There are 5 electrons in its M shell 10.
10. What is maximum capacity of a shell?
Ans. Maximum capacity of a shell is found by 2n2
formula.
Test yourself 2.4
1. Why do the isotopes of an element have different atomic masses?
Ans: The isotopes of an element have different atomic masses because they have different
number of neutrons their nucleus.
2. How many neutrons are present in C-12 and C-13?
Ans. C-12 has 6 neutrons and C-13 has 7 neutrons. Number of neutrons in an atom is found by
the formula:
Number of neutrons, n = A – Z
For C-12, n = 12- 6 = 6
For C-13, n = 13- 6 = 7
3. Which of the isotopes of hydrogen contains greater number of neutrons?
Ans. There are three isotopes of hydrogen, protium, (11H), deuterium (12H) and tritium
(13H). Tritium has greater number of neutrons (3) in its nucleus.
4. Give one example each of the use of radioactive isotope in medicine and radiotherapy?
Ans. Isotopes of Iodine-131 are used for diagnosis of goiter in thyroid gland. For cancer,
affecting within the body, Co-60 is used because it emits strongly penetrating gamma rays.
5. How is the goiter in thyroid gland detected?
Ans. The radioactive isotopes are used as tracers in medicine to diagnose the presence of tumor
in the human body. Iodine-131 is used for diagnosis of goiter in thyroid gland.
6. Define nuclear fission reaction?
Ans. A nuclear reaction in which a heavy nucleus splits into smaller parts spontaneously
or on impact with another particle. During this process large amount of energy is released.
7. When U-235 breaks up, it produces a large amount of energy. How is this energy used?

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Ans. When U-235 breaks up a large amount of energy is released which is used to convert
water into steam in boilers. The steam then drives the turbines to generate electricity.
8. How many neutrons are produced in the fission reaction of U-235?
Ans. Three neutrons are produced in the fission reaction of U-235.
9. U-235 fission produces two atoms of which elements?
Ans. The uranium nucleus breaks up to produce Barium-139 and Krypton-94.

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Test Yourself 3.1
1. What was the contribution of Dobereiner towards classification of elements?
Ans. A German chemist Dobereiner observed relationship between atomic masses of several
groups of three elements called triads. In these groups, the central or middle element had atomic
mass average of the other two elements. One triad group example is that of calcium (40),
strontium (88) and barium (137).
2. How Newlands arranged the elements?
Ans. In 1864 British chemist Newlands put forward his observations in the form of ‘law of
octaves’. He noted that there was a repetition in chemical properties of every eighth element if
they were arranged by their increasing atomic masses.
3. Who introduced the name Periodic Table ?
Ans. Russian chemist, Mendeleev introduced the name Periodic table.
4. Why the improvement in Mendeleev’s periodic table was made?
Ans. In Mendeleev’s periodic table elements were arranged according to their atomic masses. It
was found that Atomic number is a more fundamental property than atomic mass because atomic
number of every element is fixed and it increases regularly by 1 from element to element. No
two elements can have the same atomic number. So elements are arranged according to their
atomic numbers.
5. State Mendeleev’s periodic law?
Ans. According to Mendeleev’s periodic law, properties of the elements are periodic functions of
their atomic masses.
6. Why and how elements are arranged in a period?
Ans. The elements are arranged according to their atomic numbers. It was found that Atomic
number is a more fundamental property than atomic mass because atomic number of every
element is fixed and it increases regularly by 1 from element to element. No two elements can
have the same atomic number.
Test Yourself 3.2
1. How the properties of elements repeat after regular intervals?
Ans. When the elements are arranged according to increasing atomic number from left to right in
a horizontal row, properties of elements were found repeating after regular intervals such that
elements of similar properties and similar configuration are placed in the same group.
2. In which pattern modern periodic table was arranged?
Ans. The modern periodic table is based upon the arrangement of elements according to
increasing atomic number.
3. How many elements are in first period and what are their names and symbols?
Ans. There are two elements in first period their names are hydrogen and helium.
4. How many elements are placed in 4th period?
Ans. Fourth period consists of 18 elements.
5. From which element lanthanide series starts?
Ans. Lanthanide series starts from Lanthanide.
6. From which period actinides series starts?
Ans. Actinides series starts from Actinide.
7. How many elements are in 3rd period, write their names and symbols?

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Ans. Third period consist of 8 elements.
2nd
perioid
Sodium
Na
Magnesium
Mg
Aluminium
Al
Silicon
Si
Phosphorus
P
Sulphur
S
Chlorine
Cl
Argon
Ar
8. How many periods are considered normal periods?
Ans. Two periods (2nd and 3rd) are considered normal.
9. What do you mean by a group in a periodic table?
Ans. The vertical columns in the periodic table are called groups.
10. What is the reason of arranging elements in a group?
Ans. The elements of a group have similar electronic configuration i.e. same number of electrons
are present in their valence shells. The elements of a group show similar chemical properties.
11. What do you mean by periodic function?
Ans. Periodic function means repetition of properties of elements after regular intervals in
periodic table.
12. Why the elements are called s or p block elements?
Ans. Elements of group 1 and 2 have valence electrons in ‘s’ subshell. Therefore, they are called
s-block elements Elements of group 13 to 18 have their valence electrons in ‘p’ subshell.
Therefore, they are referred as p-block elements.
13. Write down the names of elements of group 1 with their symbols?
Ans. Group 1 consists of hydrogen (H), lithium (Li), sodium (Na), potassium (K), rubidium (Rb),
cesium (Cs) and francium (Fr).
14. How many members are in group 17, is there any liquid, what is its name ?
Ans. There are five elements that make Group 17 of the periodic table and consist of: fluorine
(F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Bromine (Br) is found in liquid
state at room temperature.
Test Yourself: 3.3
1. Define atomic radius?
Ans. Half of the distance between the nuclei of the two bonded atoms is referred as the
atomic radius of the atom.
2. What are SI units of atomic radius?
Ans. Picometer (pm) is the SI units of atomic radius.
3. Why the size of atoms decreases in a period?
Ans. There is gradual increase of effective nuclear charge which increases due to addition of
protons.
This force contracts the outermost shell towards the nucleus. Due to this atomic size decreases in
s period.
4. Define ionization energy?
Ans. The ionization energy is the amount of energy required to remove the most loosely bound
electron from the valence shell of an isolated gaseous atom.
5. Why the 2nd ionization energy of elements is higher than first one?
Ans. With the removal of first electron, force of attraction between nucleus and remaining outer
most electrons increases. So to remove 2nd electron more amount of energy is required.
6. What is the trend of ionization energy in a group?

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Ans. As we move down the group more and more shells lie between the valence shell and the
nucleus of the atom, these additional shells reduce the electrostatic force felt by the electrons
present in the outermost shell. Resultantly the valence shell electrons can be taken away easily.
Therefore, ionization energy of elements decreases from top to bottom in a group.
7. Why the ionization energy of sodium is less than that of magnesium?
Ans. Magnesium has 12 protons its nucleus. It attracts its outer most electrons more tightly than
sodium which has 11 protons in its nucleus. Due to this, ionization energy of sodium is less than
that of magnesium
8. Why is it difficult to remove an electron from halogens?
Ans. It is difficult to remove an electron from halogens because halogens being non metals have
high electronegativity values.
9. What is shielding effect?
Ans. The electrons present in the inner shells screen or shield the force of attraction of nucleus
felt by the valence shell electrons. This is called shielding effect.
10. How does shielding effect decrease the forces of electrostatic attractions between
nucleus and outer most electrons?
Ans. The attractions of outer electrons towards nucleus is partially reduced because of presence
of inner electrons. As a result valence electron experiences less nuclear charge than that of the
actual charge.
11. Why does the bigger size atoms have more shielding effect?
Ans. Bigger size atoms have more inner electrons to screen nuclear charge so they have more
shielding effect.
12. Why does the trend of electron affinity and electronegativity is same in a period?
Ans. These have same trend because the value of both electron affinity and electronegativity
depend upon same factor i.e. force of attraction of nucleus for electrons.
13. Which element has the highest electronegativity?
Ans. Fluorine has highest electronegativity value equal to 4.0 .

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Test Yourself: 4.1
1. Why does sodium form a chemical bond with chlorine?
Ans. An ionic bond is formed between sodium and chlorine. Sodium being metal loses one
electron. Chlorine being non metal accepts that electron. In this way, both atoms attain noble gas
electronic configuration and become stable.
2. Why does sodium lose an electron and attains +1 charge?
Ans: Sodium has only one electron in its outer most shell. It loses that electron to attain noble
gas electronic configuration.
3. How do atoms follow octet rule?
Ans. An atom can accommodate 8 electrons in its valence shell in three ways:
i. By giving valence shell electrons (if they are less than three) to other atoms.
ii. By gaining electrons from other atoms (if the valence shell has five or more electrons
in it).
iii. By sharing valence electrons with other atoms.
4. Which electrons are involved in chemical bonding?
Ans. Valence electrons are involved in chemical bonding.
5. Why does group 1 elements prefer to combine with group 17 elements?
Ans. Group 1 elements are metals. They have only one electron in their outermost shells. They
form positively charged ions by losing one electron. Group-17 elements are non metals. They
are electronegative elements with high electron affinities. They have the tendency to gain
electrons. If atoms belonging to these two groups are allowed to react, they form a chemical
bond.
6. Why chlorine can accept only 1 electron?
Ans. Chlorine has seven electrons in its valence shell. It needs only one electron to complete its
octet. So, it accepts only one electron and become stable.
Test YourSlef: 4.2
1. Give the electronic configuration of carbon atom?
Ans. The electronic configuration of carbon atom is 1s2
, 2s2
, 2p2
2. What type of elements have tendency of sharing of electrons?
Ans. When non metals allowed react with each other. They form a chemical bond by sharing of
electrons.
3. If repulsive forces dominate to attractive forces will a covalent bond form?
Ans. If repulsive forces dominate to attractive forces no bond will be bond formed. Considering
the electronic configuration of nitrogen atom, how many electrons are involved in bond
formation and
4. What type of covalent bond is formed?
Ans. In N2 molecule three electrons are involved in bonding. There is triple covalent bond
between two nitrogen atoms.
5. Point out the type of covalent bonds in the following molecules? CH4 , C2 H4 , H2 , N2 ,
and O2.
Ans.
Single covalent bond CH4, H2
Double covalent bond C2 H4 , O2

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Triple covalent bond N2
6. What is a lone pair? How many lone pairs of electrons are present on nitrogen in
ammonia?
Ans. The non-bonded electron pair available on an atom is called a lone pair. There is one lone
pair of electrons present on nitrogen in ammonia
7. Why is the BF3 electron deficient?
Ans. Boron atom has three electrons in its outer most shell. It forms three single covalent bonds
with fluorine and attains six electrons. Boron needs still two more electrons to complete its octet.
It accepts a lone pair through coordinate covalent bond from another molecule to complete its
octet.
8. What types of electron pairs make a molecule good donor?
Ans. Lone pair of electrons available on an atom in a molecule make it a good donor.
9. What is difference between bonded and lone pair of electron and how many bonded
pair of electrons are present in NH3 molecule?
Ans. The valence electrons, which are involved in chemical bonding, are termed as bonding
electrons. The non-bonded electron pair available on an atom is called a lone pair.
10. What do you mean by delta sign (δ) and why it develops?
Ans. The delta (δ) sign indicates partial positive or partial negative charge that is developed due
to unequal sharing of shared pair or bonded pair of electrons.
11. Why does oxygen molecule not form a polar covalent bond?
Ans. Both atoms in oxygen molecule (O2) attract share pair of electron equally. That’s why,
covalent bond in oxygen molecule is a not a polar.
12. Why has water polar covalent bonds?
Ans. Oxygen atom in water molecule being electronegative atom attracts shared pair of electrons
towards itself. Due to this, covalent bond between hydrogen and oxygen becomes polar.
Test Yourself 4.3
1. What type of elements form metallic bonds?
Ans. Metallic bond exists in atoms of metallic elements.
2. Why is the hold of nucleus over the outermost electrons in metals weak?
Ans. The hold of nucleus over the outermost electrons is weak because of large sized atoms and
greater number of shells in between nucleus and valence electrons. Furthermore, because of low
ionization potentials, metals have the tendency to lose their outermost electrons easily.
3. Why the electrons move freely in metals?
Ans. Because of low ionization potentials, metals have the tendency to lose their outermost
electrons easily. These loose or free electrons of all metal atoms move freely in the spaces
between atoms of a metal.
4. Which types of electrons are responsible for holdings the atoms together in metals?
Ans. Free electrons are responsible for holding the atoms together in metals.
5. Why a dipole develops in a molecule?
Ans. A dipole is developed in a molecule when shared pair of electrons are attracted unequally
by the atoms forming covalent bond.
6. What do you mean by induced dipole?
Ans. when non polar molecules come close to each other their electronic clouds repel each other.
In this way, temporary dipoles are created in the molecules. These are called induced dipole.

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7. Why are dipole forces of attraction not found in halogen molecules.
Ans. Halogens form homoatomic molecules. The bonding electrons in homoatomic molecules
are equally attracted by both atoms. This is the reason that dipole forces of attraction are not
found in halogen molecules.
8. What types of attractive forces exist between HCl molecules?
Ans. Dipole-dipole forces exist in between HCl molecules.
9. Define intermolecular forces; show these forces among HCl molecule?
Ans. The relatively weak forces which exist in between the molecules are called intermolecular
forces. The bonding and intermolecular forces of hydrochloric acid are shown below:
Test Yourself 4.4
1. Why the ionic compounds have high melting and boiling points?
Ans. Ionic compounds are made up of positively and negatively charged ions. There exist strong
electrostatic forces of attraction between oppositely charged ions. So, a great amount of energy is
required to break these forces.
2. What do you mean by malleability?
Ans. Malleability is the property by virtue of which a metal can be rolled into sheets.
3. Why are ionic compounds easily soluble in water?
Ans. Water is a polar compound. When ionic compounds are placed in water, its molecules
separate their positive and negative ions and surrounds them. In this way they become soluble.
4. What type of bond exists in sodium chloride ?
Ans. An ionic bond exists in sodium chloride.
5. Why the covalent compounds of bigger size molecules have high melting points?
Ans. Large molecules with three dimensional bonding form covalent crystals which are very
stable and hard. They have very high melting and boiling points.
6. (a): What is the electronegativity difference between the following pair of elements
(atoms).
Predict the nature of the bond between them?
H and CI (b)H and Na (c) Na and I (d) K and CI
Ans.
(i) H and CI E.N of H = 2.2, and E.N of Cl = 3.2
Electronegativity difference = 3.2 – 2.2 = 1.0 < 1.7
The bond between H and Cl will be polar covalent
(ii) H and Na E.N of H = 2.2 and E.N of Na = 0.9
Electronegativity difference = 2.2 – 0.9 = 1.3 < 1.7
The bond between H and Na will be ionic bond.
(iii) Na and I E.N of Na = 0.9 and E.N of I = 2.5
Electronegativity difference = 2.5 – 0.9 = 1.6 = < 1.7
The bond between Na and I will be covalent bond.
(iv) K and CI E.N of K = 0.8, and E.N of Cl = 3.2
Electronegativity difference = 3.2 – 0.8 = 2.4 > 1.7
The bond between K and Cl will be ionic bond.
(b) Comparing the electronegativity differences, arrange these compounds in increasing
ionic strength.
(b) Arrangement of these compounds in increasing ionic strength.

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KCl > NaI > NaH > HCl
Test Yourslef 5.1
1. Why the rate of diffusion of gases is rapid than that of liquids?
Ans. Rate of diffusion is inversely proportional to the density and intermolecular forces of a
substance. Gases have low density and weak intermolecular forces than liquids. So they have
high rate of diffusion than liquids.
2. Why are the gases compressible?
Ans. Gases are highly compressible due to empty spaces between their molecules.
3. What do you mean by Pascal. How many Pascals are equal to 1 atm?
Ans. Pressure has SI unit of Nm-2
. It is also called Pascal (Pa).
One Pascal (Pa) = 1 Nm-2
101325 Pa = 1 atm
4. Why the density of a gas increases on cooling?
Ans. As temperature decreases, the attractive forces among gas molecules increase. This results
decrease in volume and increase in density of a gas.
5. Why is the density of gas measured in g dm-3
while that of a liquid in g cm-3
?
Ans. The density of gas measured in g dm-3 while that of a liquid in g cm-3 because liquids and
solids are 1000 times denser than gases.
6. Convert the following
• 70 cm Hg to atm
• 3.5 atm to torr
• 1.5 atm to Pa.
Ans.
Conversion of 70 cm Hg to atm:
We know that
760 mm 0f Hg = 1 atm
76 cm of Hg = 1 atm 1 cm of Hg = 1/76 atm 70 cm of Hg = (1/76) x70 atm 70 cm of Hg
= 0.92 atm
Conversion of 3.5 atm to torr:
We know that , 1 atm = 760 torr 3.5 atm = 3.5x760 torr 3.5 atm = 2660 torr
Conversion of 1.5 atm to Pa We know that 1 atm = 101325Pa 1.5 atm = 101325 x 1.5 Pa
1.5 atm = 151987.5 Pa
Test Yourself 5.2
1. Is the Boyle’s law applicable to liquids?
Ans. No, Boyle’s law is not applicable to liquids because these are not compressible.
2. Is the Boyle’s law valid at very high temperature?
Ans. Yes, Boyle’s law is valid at high temperature because temperature is kept constant in this
law.
3. What will happen if the pressure on a sample of gas is raised three times and its
temperature is kept constant.
Ans. According to Boyle’s law, at constant temperature when pressure on a gas is raised three
times its volume will reduce to three times

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Test Yourself 5.3
1. Which variables are kept constant in Charles’s law?
Ans. In Charles’s law the mass of a gas and pressure are kept constant.
2. Why volume of a gas decreases with increase of pressure?
Ans. There are large empty spaces among gas molecules. When pressure is applied attractive
forces are developed. The empty spaces are reduced and gas occupies less volume.
3. What is absolute zero?
Ans. It is the temperature at which an ideal gas would have zero volume.
0K equal to -273 °C and 273 K is equal to 0°C.
4. Does Kelvin scale show a negative temperature?
Ans. No, Kelvin scale does not show a negative temperature.
5. When a gas is allowed to expand, what will be its effect on its temperature?
Ans. When a compressed gas is allowed to expand into the region of low pressure, it gets cool.
6. Can you cool a gas by increasing its volume?
Ans. No, it is not possible to cool a gas by increasing of its volume. A gas can be cooled by
decreasing its temperature.
Test Yourself 5.4
1. Why does evaporation increase with the increase of temperature?
Ans. At high temperature kinetic energy of the molecules increases so high that they overcome
the intermolecular forces and escape from liquid surface i.e.evaporate rapidly
2. What do you mean by condensation?
Ans. Condensation is a process in which a gas changes into liquid state.
3. Why is vapour pressure higher at high temperature?
Ans. At high temperature, the kinetic energy of the molecules increases enough to enable them to
vaporize and exert pressure on the surface of liquid.
4. Why is the boiling point of water higher than that of alcohol?
Ans. Boiling point of water (100 °C) is higher than that of alcohol (78 °C) because of more and
stronger hydrogen bonding in water.
5. What do you mean by dynamic equilibrium?
Ans. An equilibrium state at which the number of molecules evaporating is equal to the number
of molecules coming back (condensing) to liquid. This state is called dynamic equilibrium.
6. Why are the rates of diffusion in liquids slower than that of gases?
Ans. Stronger the intermolecular forces slower will be the rate of diffusion. The rate of diffusion
in liquids is slower than that of gases because they have very strong intermolecular forces in
them as compared to gases.
7. Why does rate of diffusion increase with increase of temperature?
Ans. The rate of diffusion increases with increase of temperature because at high temperature
molecules of a substance get high kinetic energy. The intermolecular forces also become weak.
They can move and diffuse rapidly easily from one place to another.
8. Why are the liquids mobile?
Ans. Liquids do not have definite volume. The molecules of liquids have weak intermolecular
forces as compared to solids. They are in constant state of motion. Due to this they are mobile.

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Test Yourself 5.5
1. Which form of sulphur exists at room temperature?
Ans. Rhombic sulphur exists at room temperature.
2. Why is white tin available at room temperature?
Ans. white tin is available at room temperature because above 13.2 o
C (at room temperature)
white tin is stable.
3. Why the melting point of a solid is considered its ‘identification’ characteristic?
Ans. The melting point of a solid is considered its identification characteristic because each pure
solid has definite and unique value of its melting point.
4. Why amorphous solids do not have sharp melting points while crystalline solids do
have?
Ans. Amorphous means shapeless. Solids in which the particles are not regularly arranged or
their regular shapes are destroyed are called amorphous solids. Due to this, they do not have
sharp melting points. Solids in which particles are arranged in a definite three-dimensional
pattern are called crystalline solids. They have definite surfaces or faces. Each face has definite
angle with the other. This is the reason that they have sharp melting points.
5. Which is lighter one aluminium or gold?
Ans. Aluminium is lighter than gold because of its low density.
6. Write the molecular formula of a sulphur molecule?
Ans. The molecular formula of sulphur is S8 .
7. Which allotropic form of carbon is stable at room temperature (25 °C)?
Ans. The most stable allotropic form of carbon is graphite.
8. State whether allotropy is shown by elements or compounds or both?
Ans. Allotropy is shown by elements only.

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Test Yourself 6.1
1. Why is a solution considered mixture?
Ans. It is considered a mixture as: The components of solution can be separated by physical
means. It shows the properties of its components and It has a variable composition.
2. Distinguish between the following pairs as compound or solution: (a) water and salt
solution (b) vinegar and benzene (c) carbonated drinks and acetone
Ans.
(a) water is a compound and salt solution is a solution
(b) vinegar is a solution and benzene is a compound
(c) carbonated drinks are solutions and acetone is a compound
3. What is the major difference between a solution and a mixture?
Ans. A solution exists as one phase whereas a mixture exists in more than one phase.
4. Why the alloys are considered solutions?
Ans. Alloys are considered solutions because an alloy like brass or bronze is also a
homogeneous mixture.
5. Dead sea is so rich with salts that it forms crystals when temperature lowers in the
winter. Can you comment why is it named as “Dead Sea”?
Ans. It is called the Dead Sea because its salinity prevents the existence of any life forms in the
sea.
Test Yourself 6.2
1. Does the percentage calculations require the chemical formula of the solute?
Ans. the percentage calculations does not require the chemical formula of the solute. Because
molar mass is not required in these calculations.
2. Why is the formula of solute necessary for calculation of the molarity of the solution?
Ans. It is because in molarity calculations, formula of solute is used to calculate molar mass and
moles of solute.
3. You are asked to prepare 15 percent (m/m) solution of common salt. How much amount
of water will be required to prepare this solution?
Ans. To make 15 percent (m/m) solution of common salt, 15g of salt is mixed with 85g of
water so that total mass of solution becomes 100g.
4. How much water should be mixed with 18 cm3
of alcohol so as to obtain 18 % (v/v)
alcohol solution?
Ans. To obtain 18 % (v/v) alcohol solution, 82 cm3
water is mixed in 18 cm3 of alcohol so
that total volume of solution becomes 100 cm3.
5. Calculate the concentration % (m/m) of a solution which contains 2.5 g of salt dissolved
in 50 g of water?
Ans. Mass of solution = 50 + 2.5 = 52.5g % mass / mass = mass of solute (g) x100
mass of solution (g) = 2.5 x 100 52.5 = 4.76%
6. Which one of the following solutions is more concentrated: one molar or three molar?
Ans. Three molar solution contains more amount of solute so it is more concentrated than one
molar solution.

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Test Yourself 6.3
1. What will happen if the solute-solute forces are stronger than those of solute-solvent
forces?
Ans. if the solute-solute forces are stronger than those of solute-solvent forces then solute will
remain insoluble in solvent.
2. When solute-solute forces are weaker than those of solute-solvent forces?
Ans. If solute-solute forces are weaker than those of solute-solvent forces then solute dissolves
and is solution formed.
3. Why is iodine soluble in CCI4 and not in water.
Ans. According like dissolves like principle Iodine being nonpolar substance, dissolves in a
nonpolar solvent CCl4. It does not dissolve in water. It is because water is a polar solvent.
4. Why test tube becomes cold when KNO3 is dissolved in water?
Ans. The test tube becomes cold when KNO3 is dissolved in water because dissolution of KNO3
is an endothermic process.
Test Yourself 6.4
1. What is difference between colloid and suspension?
Ans. Colloids are solutions in which solute particles are larger than those present in the true
solutions but not large enough to be seen by naked eye. The particles in such system dissolve and
do not settle down for a long time. Suspensions are a heterogeneous mixture of undissolved
particles in a given medium. Particles are big enough to be seen with naked eyes. Examples are
chalk in water.
2. Can colloids be separated by filtration, if not why?
Ans. Although particles are big but they can pass through a filter paper. Hence they can’t be
separated by filtration process.
3. Why are the colloids quite stable?
Ans. Particles of colloids do not settle down for a long time. Therefore, these are quite stable.
4. Why does the colloid show tyndall effect?
Ans. The particles of colloids are big enough to scatter the beam of light. That’s why they show
Tyndall effect.
5. What is tyndall effect and on what factors it depends?
Ans. Scattering of beam of light into different directions when passed through a colloid
solution is called Tyndall effect.
It depends upon following factors:
1) wavelength of the light
2) Size of colloid particles.
6. Identify as colloids or suspensions from the following: Paints, milk, milk of magnesia,
soap solution?
Ans. Colloids: Milk, soap solutions, Blood, Starch, albumin, ink, jelly and toothpaste
Suspensions: paints, milk of magnesia, chalk in water
7. How can you justify that milk is a colloid?

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Ans. Its particles do not settle down for a long time. It shows Tyndall effect by scattering the
beam of light. Its particles are large but can’t be seen by naked eye. Although its particles are
large but they can pass through filter paper.
Test Yourself 7.1
1. How can you justify that a reaction between magnesium and oxygen is a redox reaction,
while the reaction shows only addition of oxygen (oxidation)
2Mg + O2 2MgO
Ans. This reaction between magnesium and oxygen (oxidation) by magnesium and gain of
electrons (reduction) by oxygen. Hence, it is a redox reaction.
2. A reaction between carbon and oxygen involved only addition of oxygen (oxidation),
but, it is called a redox reaction. Comment on this.
Ans. Carbon is being oxidized as being reduced as its oxidation number decreases from 0 to +4
and oxygen is being reduced as its oxidation number decreases from 0 to -2. Both oxidation and
reduction reactions are taking place.That is why it is called redox reaction.
3. Oxidation and reduction proceed simultaneously .Explain with an example.
Ans. where there is oxidation there is reduction. Both reactions proceed simultaneously. For
example:
2Mg + O2 2MgO
In this reaction magnesium is oxidized and oxygen is reduced.
4. Identify which of the following is oxidation or reduction reaction?
a. K
b. Br + 1e
-
c. Cu
d. I
-
e. Fe
+2
K
+
+ 1e
-
Br
-
Cu
2+
+ 2e
-
I + 1e
-
Fe
+3
+ 1e
-
Ans.
(a) K involves lose of electron, so it is an oxidation reaction.
(b) Br involves gain of electron, it is a reduction reaction.
(c) Cu involves lose of electron, it is an oxidation reaction.
(d) Iodide ion loses an electron, it is an oxidation reaction.
(e) Ferric ion loses an electron. it is an oxidation reaction.
5. An element M reacts with another element X to form MX electrons, identify the
element which is oxidized and which is reduced.
Ans.
M M
+2
+ 2e
-
M atom loses two electrons, so it is oxidized
X + 2 e- X-2
X atom gain two electrons, so it is reduced
M + X MX
6. How can you justify that the following reaction is not only an oxidation reaction but
also a complete redox reaction?

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FeO + CO Fe + C02
Ans.
Removal of an oxygen atom from a molecule is reduction. Oxygen atom has removed from FeO,
so it is reduced. CO gains oxygen and is converted to CO2. It is oxidized.
7. Explain the term oxidation on the basis of electronic concept with example.
Ans. Oxidation is loss of electron by an atom or an ion e.g
Zn(s)
Zn(aq)
+2
+ 2 e-
Fe+2
(aq) Fe(aq)
+3
+ 1 e-
Test Yourself 7.2
1. Find out the oxidation numbers of the following elements marked in bold in the
Formula:Ba3(PO4)2, CaSO4, Cu(NO3)2, Al2(SO4)3
Ans.
(a) To find oxidation number of P in Ba3(PO4)2
3(oxidation number of Ba) + 2(oxidation number of P) + 8(oxidation number of oxygen) = 0
3(+2) + 2(oxidation number of P) + 8(-2) = 0
6 + 2(O.N. of P) –16 = 0
2(O.N. of P) – 10 = 0
2(O.N. of P) = 10
O.N. of P = 10/2 = 5
Oxidation number of P = 5
(b) To calculate oxidation number of S in CaSO4,
(O.N. of Ca) + (O.N. of S) + 4( O.N of O) = 0
(+2) + (oxidation number of S) + 4(-2) = 0
2 + (O.N. of S) – 8 = 0
O.N. of S – 6 = 0
Oxidation number of S = 6
(c)To calculate oxidation number of N in Cu(NO3)2
(O.N. of Cu) + 2(O.N. of N) + 6(O.N. of O) = 0
(+2) + 2(O.N. of N) + 6(– 2) = 0
2 + 2(O.N. of N) – 12 = 0
2(O.N. of N) – 10 = 0
2(O.N. of N) = 10
O.N. of N = 10/2
Oxidation number of N = 5
(d)To calculate oxidation number of S in Al2(SO4)3
2(O.N.of Al) + 3(O.N.of S) + 12(O.N.of O) = 0
2(+3) + 3(oxidation number of S) + 12(–2) = 0
6 + 3(oxidation number of S) –24 = 0
3(oxidation number of S) –18 = 0
3(oxidation number of S) = 18

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O.N. of of S = 18/3
O.N. of S = 6
2. In a compound MX3, find out the oxidation number of M and X?
Ans.
Applying formula for MX3
(O.No. of M) + 3(O.No. of X) = 0
(O.No. of M) +3(–1) = 0
O.No. of M –3 = 0
O.No. of M = 3
Applying formula for MX3
(O.No. of M) + 3(O.No. of X) = 0
3 + 3(O.No. of X) = 0
3(O.No. of X) = –3
O.No. of X = –3/3
O.No. of X = –1
3. Why the oxidation number of oxygen in OF2 is +2?
Ans. In OF2 molecule both oxygen and fluorine atoms are electronegative. Fluorine being most
electronegative atom gets negative ( –4) oxidation state and oxygen atom being less electron
negative gets positive (+2) oxidation state.
4. In H2S, SO2 and H2SO4 the sulphur atom has different oxidation number. Find out the
oxidation number of sulphur in each compound.
Ans.
(a) H2S
2(O.N of H ) + O.N of S = 0
2(+1) + O.N of S = 0
2 + O.N of S = 0
O.N of S = -2
(b) SO2
O.N of S + 2(O.N of O) = 0
O.N of S +2(–2) = 0
O.N of S –4 = 0
O.N of S = 4
(c) H2SO4
2 (O.N of H ) + (O.N of S) + 4 (.O.N of O) = 0
2 (+1) + O.N of S + 4 (-2) = 0
2 + O.N of S –8 = 0
O.N of S –6 = 0
O.N of S = 6
5. An element X has oxidation state 0. What will be its oxidation state when it gains three
electrons?
Ans. when X element gains three electrons its oxidation state changes from 0 to
It can be represented as:
X + 3 e-
X-3
6. An element in oxidation state +7 gains electrons to be reduced to oxidation state +2.
How many electrons did it accept?

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Ans. when an element in oxidation state +7 gains five (5) electrons its oxidation state
reduced to +2.
It can be represented as:
X+7
+ 5 e-
X-2
7. If the oxidation state of an element changes from +5 to oxidized? How many electrons
are involved in this process?
Ans. If the oxidation state of an element changes from +5 to -3. It has been reduced. It has
gained eight (8) electrons.
X+5
+ 8e-
X-3
Test Yourself 7.3
1. In the following reaction, how can you justify that H2S is oxidized and SO2 is reduced
SO2+ 2 HS 2H2O + 3S
Ans. Chemical equation with oxidation number
S+4
O-4
2+ 2 H+2
S-2
2H+4
2O -4
+ 3S0
From above equation we can see that oxidation number of S in H2S has changed from – 2 to 0.
So, H2S is oxidized. In SO2 oxidation number of S has changed from +4 to 0. So, SO2 is reduced.
2. The reaction between MnO2 and HCl is a redox reaction written as balance chemical
equation.
MnO2+ 4HCl MnCl2+ 2H20 + Cl2
Find out:
a. The substance oxidized.
b. The substance reduced.
c. The substance which acts as an oxidizing agent.
d. The substance which acts as a reducing agent
Ans. chemical equation with oxidation numbers
Mn+4
O-4
2+ 4H+1
Cl-1
Mn+2
Cl-2
2+ 2H+2
20-2
+ Cl0
2
The above reaction shows that
(a) HCl is oxidized.
(b) MnO2 is reduced.
(c) MnO2 acts an oxidizing agent.
(d) HCl acts as a reducing agent.
3. The following reactions are redox reactions.
Find out the element which has been reduced and the element which has been oxidized.

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Zn+ CuSO4 ZnSO4
+ Cu
Cu + 2 AgNO3 Cu(NO3)2+ 2Ag
H2S+ Cl2 2HCl + S
Ans.
(a) Chemical equation with oxidation numbers
Zn0
+ Cu+2
SO-2
4 Zn+2
SO-2
4
+ Cu0
Above reaction shows that
i. Zinc (Zn0
) is oxidized.
ii. Copper (Cu2+
)
(b) Chemical equation with oxidation numbers can be written as:
Cu0
+ 2 Ag+1
N+5
O-6
3 Cu+2
(N+10
O-12
3)2+ 2Ag0
i. Copper (Cu0
)
ii. Silver (Ag+1
) is reduced.
as an oxidizing agent with oxidation numbers can be written as:
H+2
2S-2
+ Cl0
2 2H+1
Cl-1
+ S0
i. Sulphur (S) is oxidized.
ii. Chlorine (Cl) is reduced.
5. Why the following reaction is not a redox reaction. Explain with reasons?
NaOH+ HCl NaCl + H2O
Ans. Chemical equation with oxidation numbers can be written as:
Na+1
O-2
H+1
+ H+1
Cl-1
Na+1
Cl-1
+ H+2
2O-2
It is clear from above reaction, there is no lose or gain of electrons.Therefore, no oxidation-
reduction reaction taking place. So, it is not a redox reaction.

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Test Yourself 7.4
1. Why are the strong electrolytes termed as good conductors?
Ans. Strong electrolytes are termed as good conductors because they ionize almost completely in
their solutions. The ions of electrolytes are responsible for the conduct of electricity.
2. Does non-electrolytes forms ions in solution?
Ans. Non-electrolytes do not ionize in their aqueous solutions
3. What is difference between a strong electrolyte and a weak electrolyte?
Ans.
Strong electrolyte: The electrolytes which ionize almost completely in their aqueous solutions
and produce more ions, are called strong electrolytes. Examples of strong electrolytes are
aqueous solutions of NaCl, NaOH and HCl.
Weak electrolyte: The electrolytes which ionize and could not produce more ions are called
weak electrolytes. Acetic acid (CH3COOH) and Ca(OH)2 when dissolved in water, ionize to a
small extent and are good examples of weak electrolytes.
4. Identify a strong or weak electrolytes.
CuSO4, H2CO3, Ca(OH)2 HCl, AgNO3
Ans.
Strong electrolyte CuSO4, AgNO3, HCl
weak electrolyte H2CO3, Ca(OH)2
5. Which force drives the non-spontaneous reaction to take place?
Ans. An electric force drives the non-spontaneous reaction to take place.
6. Which type of chemical reaction takes place in electrolytic cell?
Ans. A Non-spontaneous redox reaction takes place in an electrolytic cell.
7. What type of reaction takes place at anode in electrolytic cell?
Ans. An oxidation reaction takes place at anode in electrolytic cell
8. Why the positively charged electrode is called anode in electrolytic cell?
Ans. In electrolytic cell, positively charged electrode is connected to positive terminal of the
battery, that is why it is called an anode.
9. In the electrolysis of water, towards which terminal H+
ions move?
Ans. In the electrolysis of water, H+
ions move towards cathode.
10. In the electrolysis of water, where is the oxygen produced?
Ans. In the electrolysis of water, oxygen is produced at anode.
11. Towards which electrode of the electrolytic cell moves the cations and what does they
do there?
Ans. In electrolytic cell cations move toward cathode.They get reduced there by gaining
electrons.
12. How the half-cells of a galvanic cell are connected? What is function of salt?
Ans. A galvanic cell consists of two cells. Each cell is called as half-cells. These are connected
electrically by a salt bridge. In each of the half-cell, an electrode is dipped in 1 M solution of its
own salt and connected through a wire to an external circuit. The function of the salt bridge is to
keep the solutions of two half-cells neutral by providing a pathway for migration of ions.
Test Yourself 7.5
1. Anode of Downs cell is made of a non- metal, what is its name? What is the function of

Test Yourself [9th
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this anode?
Ans. Graphite acts as anode in Down’s cell.
2Cl-
Cl2
+ 2e-
The function of graphite anode is to oxidize Cl-
ions to Cl2 by taking electrons from it.
2. Where does the sodium metal is collected in Downs cell?
Ans. Sodium ions (Na+
) are reduced at cathode and molten sodium (Na) metal floats on the
denser molten salt mixture from where it is collected in a side tube.
3. What is the name of the by-product produced in the Down’s cell?
Ans. Chlorine gas (Cl2) is produced as a by-product in the Down’s cell.
4. Are anodes of Down’s cell and Nelson cell made of same element? If yes, what is its
name ?
Ans. Yes, anodes of both Down’s cell and Nelson cell are made of same element.The name
of element is graphite.
5. What is the shape of cathode in Nelson’s cell? Why is it perforated?
Ans. U-shaped iron cathode is used in Nelson’s cell. It is to be perforated for percolation of
sodium hydroxide solution slowly into a catch basin.
6. Which ions are discharged at cathode in Nelson’s cell and what is produced at
cathode?
Ans. The H+ ions are discharged at cathode and H2 gas is produced at cathode.
2H2O + 2e-
H2 + 2OH-
Test Yourself 7.6
1. What is the difference between corrosion and rusting?
Ans.
Corrosion is slow and continuous eating away of a metal by the surrounding
medium.
Corrosion is a general term but corrosion of iron is called rusting.
2. What happens to iron in the rusting process?
Ans. By rusting process the whole piece of iron is eaten away
3. Rusting completes in how many redox reactions?
Ans. The rusting of iron completes is these four steps:
(i) 2Fe(s) 2Fe+2
(aq)+ 4e-
(ii) O2 (g) + 4H+
(aq) + 2e-
2H2O(l)
(iii) 2Fe(s) + O2(g) + 4H+
2Fe+2
(aq) + 2H2O(l)
(iv) 2Fe+2
(aq) 1/2 O2(g) + (2 + n) H2O(l) Fe2O3.nH2O(s) + 4H+
(aq)
4. Explain the role of O2 in rusting?
Ans. Oxygen plays an important role in rusting.
A region of relatively high O2 concentration near the surface surrounded by water layer acts
as cathode and electrons reduce the oxygen molecule in the presence of H+
ions

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O2 (g)
+ 4H+
(aq)
+ 2e-
2H2
O(l)
This chemical reaction starts rusting of iron.
5. State the best method for protection of metal from corrosion?
Ans. The best method for protection against the corrosion of metals exposed to acidic
conditions is coating the metal with other metal. Corrosion resistant metals like Zinc (Zn),tin
(Sn) and chromium (Cr) are coated on the surface of iron to protect it from corrosion.
6. What do you mean by galvanizing?
Ans. The process of coating a thin layer of zinc on iron is called galvanizing. This process is
carried out by dipping a clean iron sheet in a zinc chloride bath and then heating it. After this
iron sheet is removed, rolled into molten zinc metal bath and finally air- cooled.
7. What is the advantage of galvanizing?
Ans. Advantage of galvanizing is that zinc protects the iron against corrosion even after the
coating surface is broken.
8. Why tin plated iron is rusted rapidly when tin layer is broken?
Ans. The tin protects the iron only as long as its protective layer remains intact. Once it is
broken and the iron is exposed to the air and water, a galvanic cell is established and iron
rusts rapidly.
9. Name the metal which is used for galvanizing iron?
Ans. Zinc metal is used for the galvanizing of iron.
Test Yourself 7.7
1. Define electroplating?
Ans. An electroplating is depositing of one metal over the other by other means of electrolysis
2. How electroplating of zinc is carried out?
Ans. The target metal is cleaned in alkaline detergent solutions and it is treated with acid, in
order to remove any rust or surface scales. Then, the zinc is deposited on the metal by
immersing it in a chemical bath containing electrolyte zinc sulphate. A current is applied,
which results in depositing of zinc on the target metal i.e. cathode.
3. Which material is used to make cathode in electroplating?
Ans. The cathode is made up of the object that is to be electroplated like some sheet made up of
iron.
4. Why is the anode made up of a metal to be deposited during electrolysis?
Ans. The anode is made of the metal, which is to be deposited like Cr, Ni. is passed, the metal
from anode dissolves in the solution and metallic ions migrate to the cathode and discharge or
deposit on the cathode (object).

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Test Yourself: 8
Sr
#
Important Metals Name of metals
1. The most abundant metal aluminium
2. The most precious metal platinum
3. The most useable metal Iron
4. The most reactive metal cesium
5. The most valuable metal uranium
6. The lightest metal lithium
7. The heaviest metal osmium
8. The least conductor of heat Lead
9. The most ductile and
malleable metals
gold and silver
10. The best conductor metals silver and gold
Test yourself 8.1
1. What type of elements are metals?
Metals are the elements (except hydrogen) which are electropositive and form cations by loosing
electrons.
2. Name a metal which exists in liquid form?
Mercury is a metal which exists in liquid form.
3. What is the nature of metal oxide?
These are basic in nature.
4. Which group of metals is highly reactive?
Alkali metals are highly reactive because they have largest size and the lowest ionization energy
values.
5. Why sodium metal is more reactive than magnesium metal?
Ans. Sodium metal is more reactive than magnesium metal due to
Sodium has bigger atomic size (186 pm ) than magnesium (160 pm)
Sodium has low ionization energy (496 kJ/mol-1
) than magnesium (738 kJ/mol-1
)
6. Name a metal which can be cut with knife?
Ans. Sodium metal can be cut with knife.
7. Name the best ductile and malleable metal?
Ans. The best ductile and malleable metals are gold and silver
8. Name the metal which is the poorest conductor of heat?
Ans. The least conductor of heat is lead.
9. What do you mean by malleable and
Ans.
A metal which can be hammered into sheets
A metal which can be drawn into wires
10. Why alkali metals are more reactive than alkaline earth metals?
Ans. Alkali metals are more reactive than alkaline earth metals because :
Alkali metals have bigger atomic sizes than alkaline earth metals

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Alkali metals have lower ionization energy than alkaline earth metals.
11. What do you mean by metallic character?
Ans. Metals have the tendency to lose their valance electrons. This property of metals is termed
as electropositivity or metallic character.
12. Why metallic character decreases along a period and increases in a group?
Ans. Along period, when we move left to right, atomic size decreases and ionization energy
increases due to which ability of a metal to lose electron decreases. From top to bottom in a
group, atomic size increases and ionization energy increases due to this ability of a metal to lose
electron increases.
Test Yourslef 8.2
1. Give the applications of silver?
Ans.
Alloys of silver with copper are widely used in making coins, silver ornaments.
Compounds of silver are widely used in photographic films and dental preparations.
Silver also has important applications in mirror industry.
2. Why is silver not used in pure form?
Ans. Being very soft metal silver is not used in pure form. It is mostly used in the form of alloys
with copper.
3. What do you mean by 24 carat gold?
Ans. Purity of gold is shown by carat. This indicates the number of partsby weight of gold that is
present in 24 parts of alloy. Twenty four carat gold is pure.
4. Why is gold used to make jewelry?
Ans. Gold is very nonreactive or inert metal. It is not affected by atmosphere. It is not even
affected by any single mineral acid or base. ornamental metal.
5. Why is platinum used for making jewelry?
Ans. Platinum is used to make jewelry items because of its unique characteristics like colour,
beauty, strength, diamonds and other gemstones, enhancing their brilliance.
6. What is difference between steel and stainless steel?
Ans.  An alloy of iron mixed with a small amount of carbon is called  An alloy of steel
with chromium and nickel is called stainless steel.
7. How is platinum used as a catalyst in automobiles and what are advantages of this use?
Ans. An alloy of platinum, palladium and rhodium is used as catalyst in automobiles as catalytic
converter. It converts most of the toxic gases (CO, NO into less harmful carbon dioxide, nitrogen
and water vapour.
Test Yourself 8.3
1. Why valency of chlorine is I?
Ans. The valency of chlorine atom is 1, as it accept one electron in its valance shell.
2. Which factor controls the non-metallic character of the elements?

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Ans. The non-metallic character depends upon the electron affinity and electronegativity of the
atom.
3. Why fluorine is more non-metallic than chlorine?
Ans. Fluorine is more non metallic than chlorine because
It is small size and has
It has high electronegativity
It has high electron affinity
4. Iodine exists in solid state, can it be beaten with hammer to form sheets?
Ans. Iodine is a non-metal. Non metals are brittle (break easily) and cannot hammer to form
sheets.
5. Can liquids and gases be brittle?
Ans. Liquids and gases cannot be brittle. Brittleness is the characteristic only solids.
Test Yourself 8.3
1. Why valency of chlorine is I?
Ans: valency of chlorine atom is 1, as it accepts only 1 electron in its outermost shell.
2. Which factor controls the non-metallic character of the elements?
Ans: metallic character depends upon the electron affinity and electronegativity of
3. Why fluorine is more non-metallic than chlorine?
Flourine is more non-metallic than chlorine because:
o It is small size and has high nuclear charge.
o It has high electronegativity than chlorine.
o It has high electron affinity than chlorine.
4. Iodine exists in solid state, can it be beaten with hammer to form sheets?
Iodine is a non-metal. Non metals are brittle (break easily) and cannot hammer to form sheets.
5. Can liquids and gases be brittle?
Ans. Liquids and gases cannot be brittle. Brittleness is the characteristic only solids.
6. Why the oxygen is called non metal?
Ans. Non-metals form negative ions (anions) by gaining electrons
2 electrons, therefore, it is a non metal
O + 2e- O-2
7. Name two non-metals which are both brittle and non-ductile
Ans. Carbon and Phosphorus are both brittle and non-ductile
8. Name the most abundant non-metal in the earth crust.
Ans. Oxygen is the most abundant non-metal in the earth crust
9. Give the non-metallic trend in halogens?
Ans. As we move from top to bottom in halogen family, electron affinity and
electronegativity decreases. Due to this, non-metalic characters also decreases.
10. Why do the non-metals accept electrons readily?
Ans.
 The non-metals accept electrons readily

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 They are highly electronegative elements.
 They have high electron affinity values.
 They accept electron to complete their octet and become stable.
11. Why non-metals do not react with dilute acids while metals do react?
Ans.
 Non-metals do not react with dilute acids because non acceptors.
 Metals react with acids by transferring gas and metal salt is formed.
12. How can we distinguish a metal from a non-metal by simple physical methods?
Ans.
Sr# Metals Non Metals
1. Almost all metals are solids Non-metals are brittle (break easily).
2. They are good conductor of heat
and electricity
Non-metals are bad conductors of
heat and electricity
3. They possess metallic luster They are not shiny
4. They are hard They are generally soft
5. They have high melting and
boiling
points
They have low melting and boiling
points
6. They have high densities They have low densities
13. How we can distinguish a substance is metal or non-metal with the help of an acid
Ans. Metals react with acid producing H2 gas and metal salt. Non metal do not react with
acids. e.g
Zn+2HCl ZnCl2 + H2
14. Why is HF a weak acid?
Ans. Strong acid is one which ionizes almost completely in its aqueous solution. HF is weak
acid because it’s very small amount dissociates into its ions. The reason of low ionization is
the presence of hydrogen bonding among HF molecules.

9th Chemistry Notes - Test Yourself (Malik Xufyan)

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