Chemistry Model Question 1

Question 1

How many electrons are there in the ultimate orbital of any inert gas?

Answer 1

8

Question 2

What is nanometer?

Answer 2

One nano meter (nm) is one billionth or 10-9m.

Question 3

Name an ore of tungsten?

Answer 3

Wolframite (FeMn) WO4,

Scheelite CaWO4

Question 4

What is added to delay the setting of cement?

Answer 4

Gypsum

Question 5

What is the hardness of diamond on Moh’s scale?

Answer 5

10

Question 6

State octet rule.

Answer 6

All the elements with an unstable or incomplete electronic configuration have a tendency
to attain the stable electronic configuration of the nearest inert gas configuration.

They obtain eight electrons in the outermost orbital either by the complete transfer of valence electron from one atom to another or by mutual sharing of valence electron between the atoms.

Question 7

Write down the modern periodic law.

Answer 7

The physical and chemical properties of the elements are periodic functions of their atomic
numbers.

Question 8

Define Lewis concept of acids and bases.

Answer 8

Lewis concept is known as the electronic concept because it involves electron pair transfer during base formation.
Lewis Acid – Electron Acceptor
Lewis Base – Electron Donor
According to this theory, an acid is a substance that accepts a pair of electrons.
So, acid is an electron pair acceptor.
A base is a substance that donates a pair of electrons.
So, a base is an electron-pair donor.

Question 9

Mention the types of colloids.

Answer 9

Depending upon the nature of the interaction between the dispersed phase and dispersion
medium, colloidal sols are divided into:
i). Lyophilic (Solvent attracting)
ii). Lyophobic (Solvent repelling)

Question 10

What are catalytic promoters?

Answer 10

A catalytic promoter is a substance that increases the catalytic activity of a catalyst.

Question 11

Define biomaterial.

Answer 11

Biomaterials are the materials that can be implanted into the body
to provide special prosthetic functions
and used in diagnostic, surgical, and therapeutic applications
without causing an adverse effect on blood and other tissues.

Question 12

Mention the composition of stainless steel.

Answer 12

Chromium-18%, Nickel-8%.

Question 13

Mention the uses of titanium.

Answer 13

1. Titanium has better corrosion resistance and is much lighter in mass when compared to stainless steel. It is therefore used in aircraft, gas turbine engines, marine equipment, etc.
2. It is also used for hardening steel.
3. TiO2 is used as a semi-precious artificial gem.

Question 14

Define powder metallurgy.

Answer 14

Powder metallurgy is the art of manufacturing fine metal powders and fabricating them into desired geometrical shapes with little or no melting and compression.
Powder metallurgical products contain not only metals but also metals and non–metals.

Question 15

What is meant by radioactive decay?

Answer 15

The spontaneous disintegration of atoms of heavy elements with emission of α particle, β particle
or both and transform into a new element is known as Radioactive decay and this is called
radioactive transformation or transmutation.

Question 16

Write down the importance of glazing in ceramics.

Answer 16

Glazing is the process of giving a smooth, glossy, non-porous surface on the articles using glazes.
A glaze is a fine powder consisting of glass-forming materials like lead silicates, borosilicate, etc.

Question 17

Define refractory.

Answer 17

Refractories are materials that can withstand very high temperatures.
They are resistant to heat and corrosive action of gases, metallic liquids, and slags.
Example: Fire clay, silica.

Question 18

What is meant by annealing of glass? Mention the importance of it.

Answer 18

The method of slow cooling of glass is called annealing.
If the manufactured hot glass articles are cooled suddenly, they will easily break,
since glass is a poor conductor of heat.
To avoid this, glass is cooled very slowly by passing that through several hot chambers.
The temperature of the hot chamber is in decreasing order gradually.
This process of slow cooling of glass is called annealing.
The annealing temperature varies for different types of glasses.

Question 19

Give any 2 defects of natural rubber?

Answer 19

The natural rubber obtained from latex cannot be used in industries because it has the following defects.

1. It becomes soft and sticky during summer.
2. It becomes hard and brittle during winter.
3. It swells up in oils.
4. It flows plastically due to prolonged stress.
5. Chemicals easily affect natural rubber.

Question 20

How is Carborundum prepared?

Answer 20

Silicon carbide (SiC) is also known as carborundum. It is a siliceous artificial abrasive. In hardness
is 9.3, it is almost equivalent to diamond
Preparation
Silicon carbide is prepared by fusing a mixture of silica (sand) and carbon (coke) with some salt
and sawdust in an electric arc furnace at 3000°C.
SiO2 + 3C –3000C—> SiC + 2CO
Sand Coke
Salt and sawdust are added to infuse air into the
product so that it can be broken into pieces easily.
The product obtained is first washed with strong acid followed by a strong base to remove basic
and acidic impurities respectively. Finally, it is washed with water.

Question 21

Explain in detail about aufbau principle for filling of electrons in an atom with a suitable example. (7)

Answer 21

Aufbau principle states that in the ground state of an atom, the orbitals are filled in the
increasing order of the energy.
In other words, electrons first occupy the lowest possible energy orbital available and enter
into higher energy orbital only after the lower energy orbital is filled. As you have learnt above, the energy of a given orbital depends upon effective nuclear charge and the type of orbitals.
Thus, there is no single ordering of energies of orbitals that is universally correct for all atoms.
However, following order orbitals is extremely useful:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s…4
The orbitals s, p, d, f are called sub-shells.
The order may be remembered by using the method given in Fig. 1.1.2.
Starting from the top, the direction of the arrows gives the order of filling of orbitals, that is
starting from top right to bottom left.
With respect to the placement of outermost valence electrons, it is remarkably accurate for all atoms.
For example, valence electron in potassium must choose between 3d and 4s orbitals and as
predicted by this sequence, it is found in 4s orbital.
K19 1s2 2s2 2p6 3s2 3p6 4s1
Sc21 1s2 2s2 2p6 3s2 3p6 4s2 3d1
The above order should be assumed to be a rough guide to the filling of energy levels.
In many cases, the orbital similar in energy and small changes in atomic structure may bring
about a change in the order of filling.For example:
Cr24 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Cu29 1s2 2s2 2p6 3s2 3p6 4s1 3d10
The reason being any orbital when it is completely filled or exactly half filled it has lower energy
and higher stability.