Integrated Guidance Programme of General Studies for IAS
(Pre) - 2013
Subject - General Science
Chapter : Gist of Chemistry from NCERT Books
Acid, Base and Salts
Acids are compounds that contain Hydrogen (Hydrochloric, HCl;
Sulphuric, H2SO4; Nitric, HNO3). However, not all compounds that contain
Hydrogen are acids (Water, H2O; Methane, CH4). Acids are usually compounds of
non metals with Hydrogen and sometimes Oxygen. Acids can be classified in
various ways, depending on the factors mentioned below:
Classification Based on the Strength of the acid.
Classification Based on the Basicity of the Acid.
Classification Based on the Concentration of the acid.
Classification Based on the presence of Oxygen.
Bases and Alkalis
A Base is a substance that gives OH- ions when dissolved in
water. Bases are usually metal hydroxides (MOH). Examples include Sodium
Hydroxide, NaOH, Calcium Hydroxide, Ca(OH)2. The solution of a base in water is
called an alkali. The strength of a base depends on the concentration of the
hydroxyl ions when it is dissolved in water.
1. Strong Base: A base that dissociates completely or
almost completely in water is classified as a strong base. The greater the
number of hydroxyl ions the base produces, the stronger is the base. Examples:
Sodium hydroxide: NaOH, Potassium hydroxide: KOH, Calcium hydroxide: Ca(OH)2.
2. Weak Base: A base that dissociates in water only
partially is known as a weak base. Examples: Magnesium hydroxide: Mg(OH)2,
Ammonium hydroxide: NH4OH.
A scale for measuring hydrogen ion concentration in a
solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in
German, meaning power. On the pH scale we can measure pH from 0 (very acidic) to
14 (very alkaline). pH should be thought of simply as a number which indicates
the acidic or basic nature of a solution. Higher the hydronium ion
concentration, lower is the pH value. The pH of a neutral solution is 7. Values
less than 7 on the pH scale represent an acidic solution. As the pH value
increases from 7 to 14, it represents an increase in OH– ion concentration in
the solution, that is, increase in the strength of alkali.
A Salt results when an acid reacts with a base. Both are
neutralised. The H+ and OH- ions combine to form water. The non metallic ions of
the acid and the metal ions of the base form the salt.
Important salts used in everyday life and industrial
applications are Sodium chloride (NaCl), Sodium carbonate, (Na2CO3), Sodium
Bicarbonate, (NaHCO3), Sodium Hydroxide (NaOH)
Chemical bonds are what hold atoms together to form the more
complicated aggregates that we know as molecules and extended solids. The forces
that hold bonded atoms together are basically just the same kinds of
electrostatic attractions that bind the electrons of an atom to its
positively-charged nucleus. chemical bonding occurs when one or more electrons
are simultaneously attracted to two nuclei.
Chemical Reactions and Equations
A change in which one or more new substances are formed
is called a chemical change. A chemical change is also called a chemical
reaction. The change may conveniently be represented by a chemical equation.
Chemical reactions occur when different atoms and
molecules combine together and split apart. For example, if Carbon (C) is
burnt in Oxygen (O2) to form Carbon Dioxide, a Chemical Reaction occurs.
This reaction can be written: C + O2—> C O2. This is called a Chemical
Equation. The substances on the left hand side of the equation are called
the Reactants. The substances on the right hand side are called the
A solution is a homogeneous mixture of two or more
substances. The major component of a solution is called the solvent, and the
minor, the solute. Lemonade, soda water etc. are all examples of solutions.
We can also have solid solutions (alloys) and gaseous solutions (air).
The particles of a solution are smaller than 1 nm (10-9 metre)
in diameter. So, they cannot be seen by naked eyes. The solute particles
cannot be separated from the mixture by the process of filtration. The
solute particles do not settle down when left undisturbed, that is, a
solution is stable.
Alloys are homogeneous mixtures of metals and cannot be
separated into their components by physical methods. But still, an alloy is
considered as a mixture because it shows the properties of its constituents
and can have variable composition. For example, brass is a mixture of
approximately 30% zinc and 70% copper.
Non-homogeneous systems, in which solids are dispersed in
liquids, are called suspensions. A suspension is a heterogeneous mixture in
which the solute particles do not dissolve but remain suspended throughout
the bulk of the medium. Particles of a suspension are visible to the naked
Organic chemistry is that branch of chemistry which deals
with the study of compounds of carbon with hydrogen (hydrocarbons), and
Organic Chemistry is essentially the chemistry of Carbon.
Carbon compounds are classified according to how the Carbon atoms are
arranged and what other groups of atoms are attached.
Hydrocarbons: The simplest Organic compounds are made up
of only Carbon and Hydrogen atoms only. Even these run into thousands!
Compounds of Carbon and Hydrogen only are called Hydrocarbons.
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Properties of Gases
First, we know that a gas has no definite volume or
shape; a gas will fill whatever volume is available to it. Contrast this to
the behavior of a liquid, which always has a distinct upper surface when its
volume is less than that of the space it occupies.
The other outstanding characteristic of gases is their
low densities, compared with those of liquids and solids. The most
remarkable property of gases, however, is that to a very good approximation,
they all behave the same way in response to changes in temperature and
pressure, expanding or contracting by predictable amounts. This is very
different from the behavior of liquids or solids, in which the properties of
each particular substance must be determined individually.
All gases expand equally due to equally due to equal
Diffusion of gases: The phenomenon in which a
substance mixes with another because of molecular motion, even against
gravity- is called diffusion.
The pressure of a gas: The molecules of a gas, being in
continuous motion, frequently strike the inner walls of their container. As
they do so, they immediately bounce off without loss of kinetic energy, but
the reversal of direction (acceleration) imparts a force to the container
walls. This force, divided by the total surface area on which it acts, is
the pressure of the gas.
The unit of pressure in the SI system is the pascal (Pa),
defined as a force of one newton per square metre (1 Nm–2 = 1 kg m–1 s–2.
Temperature scale: A reference scale with respect
to which the temperatures can be measured is known as ‘scale of
temperature’. Various scales of temperatures are in use. Important scales of
(a) Celsius scale
(b) Kelvin scale
(c) Fahrenheit scale
Celsius scale: In this scale the lowest fixed
point is the freezing temperature of pure substance. The upper fixed point
is the boiling point of water. The interval is divided into 100 divisions
all are at equal distance. Every division being denoted as one degree
Celsius (oC). The Celsius scale is also called as centigrade scale because
the range of temperature is divided into 100 equal divisions.
Kelvin scale: Another type of scale which is used
to define the measure of temperature is Kelvin scale. The Kelvin scale is
also known as absolute scale of temperature. The lowest fixed point is taken
from the lowest temperature to which a substance to be cooled such as
-273oC. According to the scale, a temperature is denoted by simply K .
Absolute zero: The temperature at which a given
mass of gas does not occupy any volume or does not exert pressure is called
the “absolute zero”. Absolute zero i.e., 0K or -273oC is the lowest possible
temperature that can be reached. At this temperature the gas has a
theoretical volume of zero. In the Kelvin scale, the lowest possible
temperature is taken as zero. This temperature is called as absolute zero.
At the point absolute zero there is no molecular motion and there is no heat
energy. At absolute-zero all atomic and molecular motions stop. Hence the
absolute zero is the lowest possible temperature which is denoted by 0K or
Fahrenheit Scale of Temperature: The lower and
upper fixed points in this scale are considered as 32o F and 212o F
respectively. The interval of 180o F is divided into 180 equal parts. Each
part is known as 1o F. This is widely used by doctors.
All gases, irrespective of their chemical composition,
obey certain laws that govern the relationship between the volume,
temperature and pressure of the gases. A given mass of a gas, under definite
conditions of temperature and pressure, occupies a definite volume. When any
of the three variables is altered, then the other variables get altered.
Thus these Gas laws establish relationships between the three variables of
volume, pressure and temperature of a gas.
Boyle’s Law: Robert Boyle (1627 - 1691) discovered this
law in 1662 and it was named after him. It can be restated as “The product
of the volume and pressure of a given mass of dry gas is constant, at
constant temperature”. P ∝ 1/ V( at constant temperature) or P X V= K (where
K is constant).
Charles’ Law: “At constant pressure, the volume of a
given mass of gas increases or decreases by 1/273 of its original volume at
32oF, for each degree centigrade rise or lowering in temperature.” Assume a
given mass of gas has a volume of V1 at a temperature T1 Kelvin at a
constant pressure, then, according to Charles’ Law we can write:
V directly proportional to T or VT=K (Constant).
Avogadro’s Law: This is quite intuitive: the volume of a
gas confined by a fixed pressure varies directly with the quantity of gas.
Equal volumes of gases, measured at the same temperature and pressure,
contain equal numbers of molecules. Avogadro’s law thus predicts a directly
proportional relation between the number of moles of a gas and its volume.
Some Common Elements & Compounds
Hydrogen: Symbol H, formula H2. The first element in
the periodic table and the most basic and common of all elements in the
universe. Over ninety percent of all the atoms in the universe are hydrogen
atoms and they are the lightest of all elements. The name hydrogen comes from
the Latin word “hydro” which means water. Scientists use the letter “H” to
represent hydrogen in all chemical equations and descriptions.
Carbon: The sixth element in the periodic table. It is
a very stable element. Because it is stable, it can be found in many naturally
occurring compounds and by itself. Scientists describe the three states of
carbon as diamond, amorphous, and graphite.
Nitrogen: It is the seventh element of the periodic
table located between carbon and oxygen. Almost eighty percent of Earth’s
atmosphere is made of nitrogen gas. Nitrogen is a clear gas that has no smell
when it is in its pure form. It is not very reactive when it is in a pure
molecule, but it can create very reactive compounds when combined with other
elements including hydrogen (ammonia). There are 7 electrons in a nitrogen atom.
Oxygen: Symbol O, formula O2. Alone, oxygen is a
colorless and odorless compound that is a gas at room temperature. Oxygen
molecules are not the only form of oxygen in the atmosphere; you will also find
oxygen as ozone and carbon dioxide. There are 8 electrons in an oxygen atom.
Oxygen is non-combustible but a good supporter of combustion. An oxide is a
compound of two elements, one of which is oxygen. It can be liquefied and
solidified. It is employed in welding process and also used in hospitals for
artificial respiration. Oxygen shows a valency of -2.
Water (H2O): Water is the only substance that can
exist simultaneously in all the three states of matter, i.e., solid, liquid and
gaseous on this earth.
Pure water is a colourless, odourless and tasteless
The density of water is 1 g cm-3 at 4oC.
The boiling point of water is 100oC at a pressure of 760
mm of Hg. The melting point of ice is 0oC at a pressure of 1 atmosphere.
Ice has a relative density of 0.92. The specific heat
capacity of water is 1 cal/g at 15oC.
Water is called the “Universal Solvent”. Almost all
substances dissolve in water to a certain extent. Hence, it known as a
universal solvent. Because of this property, it is impossible to get
chemically pure water on the earth.
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