ntse chemistry

7/26/2019 Ntse Chemistry

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Resonance Pre-foundation Programmes

(PCCP) Division

Career Care

COURSE : NTSE (STAGE-I)

CHEMISTRY

WORKSHOP TAPASYASHEET

CLASS-X


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Copyrightreserved.All right reserved. Any photocopying, publishing or reproduction of full or any part of this study material is strictlyprohibited. This material belongs to only the enrolled student of RESONANCE. Any sale/resale of this material ispunishable under law. Subject to Kota Jurisdiction only.

Subject : Chemistry NTSE STAGE-I

S. No. Topics Page No.

1. Structure of Atom 1 - 12

2. Acids, Bases and Salts 13 - 23

3. Periodic Table 24-38

4. Mole Concept 39-57

.13RPCCP


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1111PAGE # 1

STRUCTURE OF ATOM

DALTONS ATOMIC THEORY

In 1808 John Dalton proposed atomic theory of

matter assuming atoms are ultimate indivisible

particles of matter based on the law of conservation

of mass and law of definite proportion.

The important points of Daltons theory are

i) Elements consist of small indivisible particles

called atomsand atoms take part in chemical

reactions.

ii)Atoms of same element are alike in all respect.

iii)Atoms of different elements are different in all

respect.

iv)Atoms cannot be created or destroyed.

v) Atoms combine in a fixed small whole number to

form compound atoms called molecules.

Note :

The term Element was coined by Lavoisier.

a) Merits :

(i)Daltons theory explains the law of conservation of

mass (point iv) and law of constant proportion (point v).

(ii)Atoms of elements take part in chemical reaction

this is true till today.

(iii) Atoms combine in whole numbers to form

molecules (point v).

b) Demerits :

(i)The atom is no longer supposed to be indivisible.

The atom is not a simple particle but a complex one.

(ii)He could not explain that why do atoms of same

element combined with each other.

(iii)Atoms of the same element may not necessarily

be identical in all aspects.There are a number of elements whose atoms

possess different masses. All these atoms of the

same element with same atomic number but different

mass number are called isotopes.

e.g.1H1,

1H2,

1H3 are the three isotopes of hydrogen.

(iv) Atoms of different elements may not necessarily

be different in all aspects. There are a number of

elements whose atoms possess same mass

number. All these elements with different atomic

number but same mass number are called isobars.

e.g. 20Ca40

and 18Ar40

are isobars of each other.

ELECTRON

Electrons are the fundamental particles of all

substances.

a) Cathode Rays - Discovery of Electron :

The nature and existence of electron was established

by experiments on conduction of electricity through

gases.

Note :

In 1859, Julius Plucker started the study of conduction

of electricity through gases at low pressure in a

discharge tube.

A number of interesting things happen when a high

voltage (say, 10,000 V) is applied across the

electrodes of the discharge tube, and the pressure ofthe gas inside the tube is lowered.

(i)When the pressure of the gas in the discharge

tube is at atmospheric pressureand a highvoltage

is applied across the electrodes, nothing noticeable

happens. But as we lower the pressure and increase

the voltage, sparking or irregular streaks of lightare

seen in the tube. This is called positive column.

(ii) As the pressure of gas is reduced further, the length

of the positive column reduces, a fine glow can be

seen at the cathode. The dark space or gap left

between the cathode and the positive column is

called the Faradays dark space.


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2222PAGE # 2

(iii) When the pressure of gas is reduced to about 1

mm of Hg, the cathode glow moves away from the

cathode, creating a dark space between cathode and

the cathode glow. This dark space is called Crookes

dark space.

(iv) The Crookes dark space expands with further fall

in pressure at 0.1 mm of Hg. The positive column

gets split into a number of bands called striations.

(v)At pressure 0.01 mm of Hg or less, the striations

move towards the anode and vanish finally. At this

stage the glass tubes begins to glow at the end

opposite to the cathode. This phenomenon is called

fluorescence.

Thus, some sort of invisible rays travel from the

negative electrode to the positive electrode. Since the

negative electrode is called cathode, these rays were

called cathode rays. The colour of glow depends upon

the nature of the glass used. For soda glass the

fluorescence is of yellowish green colour.

b) Properties of cathode rays :

(i) Cathode rays travel in a straight line at a high

velocity and generate normally from the surface of

the cathode. If an opaque object is placed in the path

of cathode rays its shadow falls on opposite side of

the cathode. It shows that cathode rays travel in

straight lines.

Cathode

Highvoltage Anode

To vacuumpump Shadow

Object

+

Note :

Cathode rays travel with very high velocities ranging

from 109to 1011 cm per second.

(ii) They are a beam of minute material particles having

definite mass and velocity. When a light paddle wheel

is placed in the path of the cathode rays, the blades

of the paddle wheel begin to rotate. This also proves

that cathode rays have mechanical energy.

(iii) They consist of negatively charged particles.When

the cathode rays pass through an electric field, they

bent towards the positive plate of the electric field.

This indicates that cathode rays are negatively

charged.

(iv) Cathode rays can affect the photographic plate.

(v)The nature of cathode rays is independent of the

nature of gas used in discharge tube or material of

cathode.

(vi) Cathode rays are deflected in the magnetic field

also.

N

S

+

Highvoltage

Deflection ofcathode raysin magnetic field

(vii) If cathode rays are focused on a thin metal foil,

the metal foil gets heated up to incandescence.

(viii) When cathode rays fall on materials having highatomic mass, new type of penetrating rays of very

small wavelength are emitted which are called X -

rays.

Thus, investigations on cathode rays showed that

these consisted of negatively charged particles.

Note :

The negatively charged particles of cathode rays were

called negatrons by Thomson. The name negatronwas changed to electronby Stoney.

c) Characteristics of electron :

(i) Electrons are sub - atomic particles whichconstitute cathode rays.

(ii) In 1897, J.J.Thomson determined the charge to

mass (e/m) ratio of electron by studying the deflections

of cathode rays in electric and magnetic fields. The

value of e/m has been found to be 1.7588 108

coulombs/g. The e/m for electrons from different

gases was found to be the same. This indicates that

atoms of all kinds have the same kind of negatively

charged particles. Thus electrons are the common

constituents of all atoms.

Note :

A cathode ray tube is used to measure the charge tomass ratio of the electrons.


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3333PAGE # 3

(iii) Charge on the electron :

The charge (e) on an electron was determined by

Robert Millikan in 1909. Millikan found the charge on

oil drops to be -1.6 10 -19 Cor its multiples. So, thecharge on an electron is to be -1.6 10-19coulombs / unit.

(iv) Mass of an electron :

By Thomsons experiment e/m = 1.76 1011C/kg

By Millikans experiment e = 1.6 10-19C

So mass of electron (m) = 11

19

101.76

101.6

!

! "

= 9.1096 10-31kgMass of an electron in amu = 0.000549

(v) Mass of electron in comparison to that of

hydrogen :

Mass of hydrogen = 1.008 amu

= 1.008 1.66 10-24g ( since 1 amu = 1.66 10-24g )= 1.673 10-24 g

electronofMass

atomhydrogenofMass= 28

24

109.1096

10731.6

!

! "= 1837

Note :

Thus, the mass of an electron is1837

1 times the

mass of a hydrogen atom.

PROTON

a) Anode Rays Canal rays) :

It has been established that electron is a negatively

charged particle and present in all the atoms. As an

atom is electrically neutral, there must be some

positively charged particles present in the atom to

neutralize the negative charges of the electrons. It

has been confirmed by experiments. Scientist

Goldstein in 1886 discovered the existence of a new

type of rays in the discharge tube. He carried out the

experiment in discharge tube containing perforated

cathode. It was observed that when high potential

difference was applied between the electrodes, not

only cathode rays were produced but also a new type

of rays were produced simultaneously from anode,moving from anode towards cathode and passed

through the holes of cathode.

Anode rays

Anode Perforated cathode

High voltage source

Fluorescence

Note :

Anode rays are called canal rays because they pass

through the canals or holes of the cathode. These

rays are also called anode rays since they originate

from the anode side. Anode rays are produced from a

positively charged electrode, therefore these were

named positive rays by J.J.Thomson.

b) Characteristics of Anode Rays :

(i) Anode rays travel in straight lines.

(ii)These rays rotate the light paddle wheel placed in

their path. This shows that anode rays are made up

of material particles.

(iii)Anode rays are deflected by magnetic or electric

field. In the electric field they get deflected towards

negatively charged plate. This indicates that these

rays arepositively charged.

(iv)The anode rays affect photographic plate.

(v) The nature of anode rays depend upon the type of

gas used.

c) Discovery of Proton :

J.J.Thomson in 1906, found that particles obtained

in the discharge tube containing hydrogen have e/m

value as 9.579 10 4 coulomb/g. This was the

maximum value of e/m observed for any positive

particle. It was thus assumed that the positive

particles given by hydrogen represent fundamental

particle of positive charge. This particle was named

proton.

H ##$#"e H+(Proton)

Note :

The name protonwas given by Rutherford in 1911.

d) Characteristics of Proton :

(i)A proton is a sub - atomic particle which constitute

anode rays produced when hydrogen is taken in the

discharge tube.

(ii) Charge of a proton :

Proton is a positively charged particle. The charge on

a proton is equal but opposite to that on an electron.

Thus, the charge on a proton is+1.602 10 19

coulombs/ unit.

(iii) Mass of a proton :

The mass of a proton is equal to the mass of a

hydrogen atom.

mp

= 1.0073 amu

= 1.673 10-24g

= 1.673 10-27

kg


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4444PAGE # 4

(iv) Mass of proton relative to mass of electron :

electronanofMass

protonaofMass=

g109.1

g101.67328

24

"

"

!

!= 1837

Thus, the mass of a proton is 1837 times larger than

the mass of an electron.

(v) Charge to mass ratio for a proton :The e/m of

particles constituting the anode rays is different fordifferent gases.

m

eof proton = 24

19

011.673

101.602"

"

!

! = 9.579 104C/g

THOMSON MODEL OF AN ATOM

J.J. Thomson (1898) tried to explain the structure of

atom. He proposed that an atom consists of a sphere

of positive electricity in which electrons are embedded

like plum in pudding or seeds evenly distributed in

red spongy mass in case of a watermelon. The radius

of the sphere is of the order 108

cm.

a) Merits :

(i) Thomsons model could explain the electricalneutrality of an atom.

(ii) Thomsons model could explain why onlynegatively charged particles are emitted when a metal

is heated as he considered the positive charge to beimmovable by assuming it to be spread over the total

volume of the atom.

(iii)He could explain the formation of ions and ionic

compounds.

b) Demerits :

This model could not satisfy the facts proposed by

Rutherford through his alpha particle scattering

experiment and hence was discarded.

RUTHERFORD MODEL OF AN ATOM

a) Rutherfords Alpha Particle Scattering

Experiment 1909) :

Ernest Rutherford and his coworkers performed

numerous experiments in which %- particles emittedfrom a radioactive elementsuch as polonium were

allowed to strike thin sheets of metals such as gold or

platinum.

(i)A beam of%-particles (He2+) was obtained by placingpolonium in alead boxand letting the alpha particles

come out of a pinhole in the lead box. This beam of %-rays was directed against a thingold foil (0.0004 cm).

A circular screen coated withzinc sulphide was placedon the other side of the foil.

(ii)About 99.0% of the %-particlespassed undeflectedthrough the gold foil and caused illumination of zincsulphide screen.

(iii)Very few %-particles underwent small and large

deflections after passing through the gold foil.

(iv) A very few (about 1 in 20,000) were deflected

backward on their path at an angle of 180.

Rutherford was able to explain these observations

as follows:

(i)Since a large number of %-particles pass throughthe atom undeflected, hence, there must be large

empty space within the atom.

(ii)As some of the %-particles got deflected, therefore,there must be something massive and positively

charged structure present in the atom.

(iii)The number of%-particleswhich get deflected isvery small, therefore, the whole positive charge in the

atom is concentrated in a very small space.

(iv) Some of the %-particles retracted their path i.e.came almost straight back towards the sources as a

result of their direct collisions with the heavy mass.

Note :

% - particles are made up of two protons and twoneutrons and are Helium (He) nuclei.

b) Rutherford Nuclear Model of Atom 1911) :

Rutherford proposed a new picture of the structure of

atom.

Main features of this model are as follows-

(i) The atom of an element consists of a small

positively charged Nucleuswhich is situated at thecentre of the atom and which carries almost the entire

mass of the atom.

(ii) Theelectrons are distributed in the empty spaceof the atom around the nucleus in differentconcentric

circular paths (orbits).


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5555PAGE # 5

(iii) The number of electrons in the orbits is equal to

the number of positive charges (protons) in the

nucleus.

(iv) Volume of nucleus is very small as compared to

the volume of atom.

(v) Most of the space in the atom is empty.

Note :Rutherfords model is also called Planetary model.

c) Defects in Rutherfords Model :

(i) Rutherford did not specify the number of electrons

in each orbit.

(ii)According to electromagnetic theory, if a charged

particle (like electron) is accelerated around another

charged particle (like protons in nucleus) then there

would be continuous loss of energy due to continuous

emission of radiations. This loss of energy would

slow down the speed of electronand eventually the

electron would fall into the nucleus. But such acollapse does not occur. Rutherfords model couldnot explain this theory.

(iii) If the electron loses energy continuously, the

observed spectrum should be continuous but the

actual observed spectrum consists of well defined

lines of definite frequencies. Hence the loss of energy

is not continuous in an atom.

BOHR MODEL OF AN ATOM (1913)

To overcome the objections to Rutherfords model

and to explain the hydrogen spectrum, Bohr proposeda quantum mechanical model of the atom.

The important postulates on which Bohrs model isbased are the following -

(i) The atom has a nucleus where all the protons are

present. The size of the nucleus is very small. It is

present at the centre of the atom.

(ii) Each stationary orbit is associated with a definite

amount of energy. The greater is distance of the orbit

from the nucleus, more shall be the energy associated

with it. These orbits are also called energy levels and

are numbered as 1, 2, 3, 4 ------or K, L, M, N ---- fromnucleus to outwards.

(iii)By the time, the electron remains in any one of the

allowed stationary orbits, it does not lose energy.

Such a state is called ground or normal state.

(iv)The emission or absorption of energy in the form

of radiation can only occur when an electron jumps

from one stationary orbit to another.

'E = Efinal

- Einitial

= h(

Where h is Plancks constant (h = 6.625 1034Js)Energy is absorbed when the electron jumps from

lower to higher orbit and is emitted when it moves

from higher to lower orbit.

When the electron moves from inner to outer orbit by

absorbing definite amount of energy, the new state of

the electron is said to be excited state.

(v)Negatively charged electrons revolves around the

nucleus in circular path. The force of attraction

between the nucleus and the electron is equal to

centrifugal force of the moving electron.

Force of attraction towards nucleus = Centrifugal force

(vi)Out of infinite number of possible circular orbits

around the nucleus, the electron can revolve only in

those orbits whose angular momentum is an integral

multiple of)2

h, i.e. mvr = n

)2

h

where :

m = mass of the electron

v = velocity of electron

r = radius of the orbit, and

n =1,2,3 ---- number of the orbit.

The angular momentum can have values such as

)2

h,

)2

h2,

)2

h3, but it cannot have a fractional value.

Thus, the angular momentum is quantized. The

specified circular orbits (quantized) are called

stationary orbits.

RADII OF VARIOUS ORBITS

Radii of various orbits can be given by formula.

r = 22

22

mkZe4

hn

)

Note :

Greater is the value of nlarger is the size of atom.

On the other hand, greater is the value of Zsmaller

is the size of the atom.

For hydrogen atom, Z = 1; so r = 22

22

mke4

hn

)

Now putting the values of h, ), m, e and k.

r = 2199312

2342

)106.1()109()101.9()14.3(4

)10625.6(n

!!!!!!!

!!

= 0.529 n2 10

10m = 0.529 n2= 0.529 108 n2cm

Thus, radius of 1storbit

= 0.529 108 12 = 0.529 108cm

= 0.529 1010m = 0.529

Radius of 2nd orbit

= 0.529 108 22= 2.11 108cm

= 2.11 1010m = 2.11

Radius of 3rd orbit

= 0.529 108 32= 4.76 108cm

= 4.76 1010m = 4.76


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6666PAGE # 6

Energy of an electron in Bohrs orbit can be givenby the formula :

E = 22

4222

hn

meKZ2

)

For hydrogen atom, Z = 1So,

22

422

hn

mek2E )

*

Putting the values of ), k, m, e and h.

E = 2342

41931292

)10625.6(n

)106.1()101.9()109()14.3(2

!!

!!!!!!!

= 2

19

n

1079.21 !J per atom

= 2n

6.13 eV per atom (1 J = 6.2419 1018eV)

Note :

The negative sign indicates that the electron is under

attraction towards nucleus, i.e. it is bound to the

nucleus.

The electron has minimum energy in the first orbit

and its energy increases as n increases, i.e., it

becomes less negative. The electron can have a

maximum energy value of zero when n = +. The zeroenergy means that the electron is no longer bound tothe nucleus , i.e. , it is not under the force of attraction

towards nucleus.

VELOCITY OF AN ELECTRON IN BOHR'S ORBIT

Velocity of an electron in Bohr s orbit can be given bythe formula :

v =n

Z ,

,

-

.

//

0

1 )

h

e2 2

Substituting the values of h, ), e.

v =n

Z 27

210

106.625

)104.8(3.142"

"

!

!!

v =nZ 2.188 108 cm/sec ----------- (iii)

v =n

10188.2 8!cm/sec (For hydrogen , Z = 1)

v1= 2.188 108cm/sec

v2=

2

1 2.188 108cm/sec = 1.094 108 cm/sec

v3=

3

1 2.188 108cm/sec = 0.7293 108cm/sec

Here v1, v

2and v

3are the velocities of electron in first,

second and third Bohr orbit in hydrogen.

NEUTRONS

In 1932, James Chadwick bombarded the element

beryllium with%- particles. He observed the emissionof a radiation with the following properties -

(i) The radiation was highly penetrating.

(ii)The radiation remained unaffected in the electricor magnetic field i.e. the radiation was neutral.

(iii)The particle constituting the radiation had the same

mass as that of the proton.These neutral particles

were called neutrons.

)(Beryllium

Be94 +

particle)(

He42

"

#$#

(Carbon)

C126 +

(Neutron)

n10

COMPARATIVE STUDY OF ELECTRON,

PROTON AND NEUTRON

Property Electron Proton Neutron

Symbol e p n

Nature Negatively charged Positively charged Neutral

Relative

charge-1 +1 0

Absolute

charge 1.602 10-19C +1.602 10-19C 0

Relative

mass1 1

Absolute

mass9.109 10-28g 1.6725 10-24g 1.6748 10-24g

1837

1

ATOMIC STRUCTURE

An atom consists of two parts -

(a) Nucleus

(b) Extra - nuclear region

a) Nucleus :

Nucleus is situated at the centre of an atom. All the

protons & neutrons are situated in the nucleus,

therefore, the entire mass of an atom is almost

concentrated in the nucleus. The overall charge of

nucleus is positive due to the presence of positively

charged protons (neutrons have no charge). The

protons & neutrons are collectively called nucleons.

Note :

The radius of the nucleus of an atom is of the order of

1013cm and its density is of the order of 10 14g/cm3.

b) Extra Nuclear Region :

In extra nuclear part or in the region outside the

nucleus, electronsare present which revolve around

the nucleus in orbits of fixed energies. These orbits

are called energy levels. These energy levels are

designated as K, L, M, N & so on.

(i)The maximum number of electrons that can be

accommodated in a shell is given by the formula

2n2.(n = shell number i.e. 1,2,3 -------)


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7777PAGE # 7

Shell n 2n2

max. no.of electrons

K 1 2(1)2

2

L 2 2(2)2

8

M 3 2(3)2

18

N 4 2(4)2

32

K L

2 8

M N

18 32+N

ucleu

s Electron shells

Maximum number ofelectrons which can beaccommodated in thevarious shells

First energy level

Second energy levelThird energy level

Fourth energy level

(ii)Each energy level is further divided into subshells

designated as s,p,d,f .

1st shell (K) contains 1 subshell (s)

2nd shell (L) contains 2 subshells (s,p)

3rd shell (M) contains 3 subshells (s,p,d)

4th shell (N) contains 4 subshells (s,p,d,f).

(iii) Shells are divided into sub-shells, sub shellsfurther contain orbitals.

(A)An orbital may be defined as

A region in the three - dimensional space around the

nucleus where the probability of finding the electron is

maximum.

(B)The maximum capacity of each orbital is that of two

electrons.

Note :

The maximum number of orbitals that can be present

in a shell is given by the formula n2.

(C) Types of orbitals :

(1) s-orbitals :The s-subshell contains just one orbital

which is non-directional & spherically symmetrical in

shape. The maximum number of electrons which can

be accommodated in s-orbital is 2.

Z

X

Y

s- orbital

(2) p - orbitals : The p-subshell contains threeorbitals which have dumb-bell shape and a directionalcharacter. The three p-orbitals are designated as p

x,

py& pzwhich are oriented in the perpendicular axis(x,y,z).The maximum number of electrons which canbe accommodated in the p subshell is 6 (2 electronsin each of three orbitals).

yy

px

z

x

y

py

z

x

pz

y

z

x

(3) d - orbitals :The d-subshells contains 5 orbitals whichare double dumb-bell in shape. These orbitals are

designated as dxz, dxy, dyz, 22 yxd " , 2zd .The d-subshell

can accommodate a maximum of 10 electrons.

yx

dxy

z

yx

dxz

z

yx

dyz

z

z

22

z

dz2

x yyx

dx y

(4) f-orbitals : The f-subshell contains7 orbitalswhichare complex in structure.The f-subshell canaccommodate a maximum of 14 electrons.

Note :

Letters s, p, d & f have originated from the wordssharp, principal, diffused & fundamental respectively.(iv) Differences between orbit and orbital :

S.No. Orbit Orbital

1It is well defined circular path around thenucleus in which the electron revolves.

It is a region in three dimensional spacearound the nucleus where the probability

of finding electron is maximum.

2 It is circular in shape.s,p and d-orbitals are spherical, dumb-bell

and double dumb-bell in shape respectively.

3It represents that an electron moves

around the nucleus in one plane.

It represents that an electron can move around

nucleus along three dimensional space (x,y and z

axis).

4

It represents that position as well as

momentum of an electron can be known

simultaneously with certainty. It is against

Heisenberg's uncertainty principle.

It represents that position as well as momentum

of an electron cannot be known simultaneously

with certainty. It is in accordance with Heisenberg's

uncertainty principle.

5

The maximum number of electrons in an

orbit is 2n2

where 'n' is the number of theorbit.

The maximum number of electrons in an orbital is

two.


10/59

8888PAGE # 8

Note :

Heisenbergs uncertainty principle - It is impossible

to determine exactly and simultaneously both the

position and momentum (or velocity) of an electron

or of any other moving particle.

QUANTUM NUMBERS

To describe the position and energy of electron in an

atom, four numbers are required, which are known

as quantum numbers.Four quantum numbers are :

(a) Principal quantum number

(b) Azimuthal quantum number(c) Magnetic quantum number

(d) Spin quantum number

a) Principal Quantum Number :

(i) It is denoted by n.

(ii) It represents the name, size and energy of the

orbit or shell to which the electron belongs.

(iii)Higher is the value of n, greater is the distanceof the shell from the nucleus.

r1< r

2< r

3< r

4< r

5< ----

(iv)Higher is the value of n, greater is the magnitudeof energy.

E1< E

2< E

3< E

4< E

5----

(v) Maximum number of electrons in a shell is given

by 2n2.

Shell Max. number of electrons

First (n =1) 2 12= 2Second (n = 2) 2 22= 8Third ( n = 3) 2 32= 18Fourth ( n = 4) 2 42= 32

(vi) Angular momentum can also be calculated using

principal quantum number.

2

nhmvr*

(vii)Value of n is from 1 to +

(viii)Every shell is given a specific alphabetic name.

First shell (n = 1) is known as K shell.

Second shell (n = 2) is known as L shell.

Third shell (n = 3) is known as M shell and so on.

Note :

Principal quantum number was given by Bohr.

b) Azimuthal Quantum Number :

(i)It is represented by !.

Note :

Azimuthal quantum number is also called angular

quantum number, subsidiary quantum number or

secondary quantum number.

(ii)For a given value of n values of !are from 0 to n

1

Value of n Values of !

1 (1st shell) 0

2 (2nd shell) 0,1

3 (3rd shell) 0,1,2

4 (4th shell) 0,1,2,3

(iii) It represents the sub-shell present in shell.

!= 0 represents s sub shell.

!= 1 represents p sub shell.

!= 2 represents d sub shell.

!= 3 represents f sub shell.

(iv) Number of sub-shell in a shell = Principal quantumnumber of shell.

(v)Maximum value of !is always less than the valueof n. So 1p, 1f, 2d, 2f, 3f subshells are not possible.s will start from 1sp will start from 2pd will start from 3df will start from 4f

(vi) Relative energy of various sub-shell in a shell areas follows -s < p < d < f

(vii)Subshells having equal ! values but with different n

values have similar shapes but their sizes increasesas the value of nincreases. 2s-subshell is greater insize than 1s- subshell. Similarly 2p, 3p, 4p subshells

have similar shapes but their sizes increase inorder 2p < 3p < 4p.

(viii)Maximum no. of electrons present in a subshell

= 2 (2!+1)

Subshell Max. electrons

s (!= 0) 2 (2 0 +1) = 2p (!= 1) 2 (2 1 +1) = 6d (!= 2) 2 (2 2 +1) = 10f (!= 3) 2 (2 3 +1) = 14

Note :Azimuthal quantum number was given bySommerfeld.

c) Magnetic quantum number :

(i)It is denoted by m.

(ii)It represents the orbitals present in sub-shell. Anorbital can be defined as :

Region in the three - dimensional space around thenucleus where the probability of finding an electron ismaximum.

(iii)For a given value of !, values of m are from !

through 0 to +!.

! m

0 01 1, 0, +1

2 2, 1, 0, +1, +23 3, 2, 1, 0, +1, +2, +3

(iv) Maximum number of orbitals in a sub-shell

= (2!+1)

Sub shell Orbitals

s (!= 0) (2 0 +1) = 1p (!= 1) (2 1 +1) = 3d (!= 2) (2 2 +1) = 5f (!= 3) (2 3 +1) = 7

(v) Maximum number of orbitals in a shell = n2

Shell Max. orbitalsFirst (n = 1) 12= 1Second (n = 2) 22= 4Third (n = 3) 32= 9

Fourth (n = 4) 42= 16


11/59

9999PAGE # 9

(vi) It represents the orientation of orbital in threedimensional space.Whenl = 0, m = 0, i.e. one value implies that ssubshell has only one space orientation and hence,it can be arranged in space only in one way along x,yor z axis. Thus, sorbital has a symmetrical sphericalshape.

Z

X

Y

s- orbital

When != 1,mhas three values 1, 0, +1 . It impliesthat psubshell of any energy shell has three spaceorientations, i.e. three orbitals. Each p-orbital hasdumb-bell shape. Each one is disposedsymmetrically along one of the three axis. p orbitalshave directional character.

orbital Pz

Px

Py

m 0 1 1

yy

px

z

x

y

py

z

x

pz

y

z

x

When != 2 mhas five values 2, 1, 0, +1, +2. Itimplies that d-subshell of any energy shell has fiveorientations, i.e. five orbitals. All the five orbitals arenot identical in shape. Four of the d-orbitals

dxy

, dyz

, dzx

, 22 yxd contain four lobes while fifth orbital

dz2consists of only two lobes.

yx

dxy

z

yx

dxz

z

yx

dyz

z

z

22

z

dz2

x yyx

dx y

There are seven f-orbitals designated as

2yzf , 2xzf , 3zf , ),yx(x 22

f ),yx(y 22f

),yx(z 22f and xyzf .

Their shapes are complicated ones.

(vii) Characteristics of orbitals :

(A) All orbitals of a subshell possess same energyi.e., they are degenerate.

(B)All orbitals of the same shell differ in the directionof their space orientation.

(C)Total number of orbitals in a shell is equal to n 2.

Note :

Magnetic quantum number was given by Zeeman.

d) Spin Quantum Number :

(i)It is denoted by s.

(ii)It represents the direction of spin of electron around

its own axis.

(iii)Clockwise spin is represented by +1/2 or 2andanticlockwise by 1/2 or 3.

(iv) Maximum two electrons with opposite spin canbe placed in an orbital.

(v) Electrons with same spin are called spin parallel

and those with opposite spin are called spin paired.

Note :

Spin quantum number was given by Gold Schmidt.

ELECTRONIC CONFIGURATION OF AN ATOM

(i)The arrangement of the electrons in different shells

is known as the electronic configuration of the

element.

(ii)Each of the orbits can accommodate a fixed number

of electrons.Maximum number of electrons in an orbit

is equal to 2n2,where nis the number of the orbit.

(iii)Electrons are filled in the increasing order of energy,

i.e. K < L < M < N ......

(iv)In the outermost shell of any atom, the maximum

possible number of electrons is 8, except in the first

shell which can have at the most 2 electrons.

Note :

If the outermost shell has its full quota of 8 electrons

it is said to be an octet. If the first shell has its full

quota of 2 electrons, it is said to be duplet.

The pictorial representation of Bohrs model ofhydrogen, helium, carbon, sodium and calcium atoms

having 1, 2, 6, 11 and 20 electrons respectively are

shown in the figure where the centre of the circle

represents the nucleus.


12/59

10101010PAGE # 10

a) Significance of Electronic Configuration :

The electronic configuration of an atom plays an

important role in determining thechemical behaviour

of an element.

(i) When the atoms of an element have completely

filled outermost shell, the element will be chemically

unreactive. For example thenoble gases (He, Ne, Ar,

Kr, Xe and Rn)have completely filled outermost shell

i.e. contains 8 electrons (except helium which has

two valence electrons) in outermost shell.

(ii) When the atom of an element has less than 8

electrons in its outermost shell, the element will be

reactive.

ORDER OF FILLING OF ELECTRONS IN SUBSHELLS

There are different rules governing the filling of

subshells. They are described briefly as follows -

a) Aufbau Principle :

The filling of subshells in atoms is based on their

energies. Electrons first occupy the subshell with

lowest energy and progressively fill the other

subshells in increasing order of energy.

Note :

The subshell with lowest energy is filled first.

The order of energy of different subshells of an atom is -

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p

< 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p.

The number present before the subshells like 1,2,3

------ represents the number of the shell i.e. n.

The order of fil l ing of different sub-shells is

representeddiagrammatically as follows :

1s

2s 2p

3p 3d

4d

5d 5f

4f

6d

4p

5p

6p

7p

3s

4s

5s

6s

7s

b) Paulis Exclusion Principle :

According to Paulis exclusion principle an orbital

cannot accommodate more than two electrons. If

there are two electrons in an orbital they must haveopposite spins.

c) Hunds Rule of Maximum Multiplicity :

According to this rule :

no electron pairing takes place in the orbitals withequivalent energy until each orbital in the given

subshell contains one electron & the spins of all

unpaired electrons are parallel i.e. in the same

direction.

Electronic configuration of some elements -

Atomic

number

Sym bol of

the element

Name of

the element

Electronic

configuration

1 H Hydrogen 1s1

2 He Helium 1s2

3 Li Lithium 1s2, 2s

1

4 Be Beryllium 1s2, 2s

2

5 B Boron 1s2, 2s

2, 2p

1

6 C Carbon 1s2, 2s

2, 2p

2

7 N Nitrogen 1s 2, 2s 2 , 2p 3

8 O Oxygen 1s 2, 2s 2 , 2p 4

9 F Fluorine 1s2, 2s

2, 2p

5

10 Ne Neon 1s2, 2s

2, 2p

6

11 Na Sodium 1s2, 2s

2, 2p

6,3s

1

12 Mg Magnes ium 1s2, 2s

2, 2p

6,3s

2

13 Al Alum inium 1s2, 2s 2 , 2p 6 ,3s 2 ,3p 1

14 Si Silicon 1s2, 2s

2, 2p

6,3s

2,3p

2

15 P Phosphorus 1s2, 2s

2, 2p

6,3s

2,3p

3

16 S Sulphur 1s2, 2s

2, 2p

6,3s

2,3p

4

17 Cl Chlorine 1s2, 2s

2, 2p

6,3s

2,3p

5

18 Ar Argon 1s2, 2s

2, 2p

6,3s

2,3p

6

19 K Potas s ium 1s 2, 2s 2 , 2p 6 ,3s 2 ,3p 6,, 4s 1

20 Ca Calcium 1s2, 2s

2, 2p

6,3s

2,3p

6,, 4s

2

21 Sc Scandium 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

1, 4s

2

22 Ti Titanium 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

2, 4s

2

23 V Vanadium 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

3, 4s

2

24 Cr Chrom ium 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

5, 4s

1

25 Mn Manganes e 1 s2, 2s 2 , 2p 6 ,3s 2 ,3p 6,3d 5, 4s 2

26 Fe Iron 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

6, 4s

2

27 Co Cobalt 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

7, 4s

2

28 Ni Nickel 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

8, 4s

2

29 Cu Copper 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

10, 4s

1

30 Zn Zinc 1s2, 2s

2, 2p

6,3s

2,3p

6,3d

10, 4s

2

VALENCE SHELL AND VALENCE ELECTRONS

The outermost shell of an atom is known as the

valence shell. The electrons present in the valence

shell of an atom are known as valence electrons.

The remainder of the atom i.e. the nucleus and other

electrons is called the core of the atom. Electrons

present in the core of an atom are known as core

electrons.e.g.

The electronic configuration of the sodium (Na) atom

is :-

Na (11) K L M

2 8 1

Thus, valence electron in Na atom = 1 and core

electrons in Na atom = 2 + 8 = 10

a) Significance of Valence Electrons :

(i) The valence electrons of an atom are responsiblefor, and take part in, chemical changes.

(ii) The valence electrons in an atom determine themode of chemical combination.


13/59

11111111PAGE # 11

(iii) The valence electrons determine the combining

capacity or the valency of the atom. The number of

electrons in an atom that actually take part in bond

formation is known as the valency of the element.

e.g. In the carbon atom, there are four valence

electrons.

C(6) K L

2 4

The carbon atom is capable of forming four bonds.Hence, the valency of carbon is four.

(iv) If the outermost shell of an atom iscompletely

filled, its valency is zero.

The outermost shells of helium, neon, argon, krypton

etc. are completely filled. Hence the valency of these

elements iszero.

(v) Elements having the same number of valence

electrons in their atoms possess similar chemical

properties.

e.g.All alkali metals have one valence electron in

their atoms. Hence, their chemical properties aresimilar.

(vi) Elements having different number of valence

electrons in their atoms show different chemical

properties.

e.g.Let us consider the electronic configuration of

alkali metals and halogens. Alkali metal atoms have

single valence electron whereas halogen atoms have

seven valence electrons. It is observed that the

chemical propertiesof the alkali metals are entirely

differentfrom those of halogens.

(vii) The number of the valence shell in the atom of an

element determines the period number of theelement in the periodic table.

e.g. Sodium (Na) :

Valence shell number = 3.

period number = 3

Calcium (Ca)

Valence shell number = 4

period number = 4

(viii) Elements with 1, 2 or 3 valence electrons in their

atoms are metals.

Note :

Hydrogen and helium are exceptions to this rule.

Hydrogen and helium atoms have 1 and 2 valenceelectrons respectively, but they are non-metals.

(ix) Elements with 4, 5, 6, 7 or 8 valence electrons in

their atoms are non metals.

e.g.carbon (C), nitrogen (N) and oxygen (O) are non

metals.

6C = 2,4

7N = 2,5

8O = 2,6

Note :

Whether the atom while combining with other atoms

can form ionic or covalent bonds is determined by

the number of valence electrons present in the atom.

VALENCY

Valency of an element is the combining capacity of

the atoms of the element with atoms of the same or

different elements. The combining capacity of the

atoms was explained in terms of their tendency to

attain a fully filled outermost shell (stable octet or

duplet)

Note :

The number of electrons gained, lost or contributed

for sharing by an atom of the element gives us directly

the combining capacity or valency of the element.

Valency of an element is determined by the number

of valence electrons in an atom of the element.

The valency of an element = number of valence

electrons (if the number of valence electrons is1 to 4)

The valency of an element = 8number of valence

electrons. (if the number of valence electrons is 4 to 8)

ISOTOPES

The isotopes of an element have the same atomic

number but different atomic masses.

Note :

The term isotope was given by Margaret Todd.

Thedifference in their masses is due to the presence

of different number of neutrons.

e.g. Isotopes of hydrogen :

Hydrogen

isotopes

1. Atomic number 1 1 1

2. No. of protons 1 1 1

3. No. of electrons 1 1 1

4. Mass number 1 2 3

5. No. of neutrons 0 1 2

H

otiumr

H21

Deuter ium

H31

Tritium

Isotopes of oxygen :

Oxygen isotopes

1. Atomic number 8 8 8

2. No. of protons 8 8 8

3. No. of electrons 8 8 8

4. Mass number 16 17 18

5. No. of neutrons 8 9 10

O168 O17

8 O18

8

Note :

All the isotopes of an element have identical chemical

properties.


14/59

12121212PAGE # 12

a) Characteristics of Isotopes :

(i) The physical properties of the isotopes of an

element are different. This is due to the fact that

isotopes have different numbers of neutrons in their

nuclei. Hence mass, density and other physical

properties of the isotopes of an element are different.

(ii)All the isotopes of an element contain the same

number of electrons. So, they have the sameelectronic configuration with the same number of

valence electrons. Since the chemical properties of

an element are determined by the number of valence

electrons in its atom, all the isotopes of an element

have identical chemical properties.

b) Reason for the Fractional Atomic Masses

of Elements :

The atomic masses of many elements are in fraction

and not whole number. The fractional atomic masses

of elements are due to the existence of their isotopes

having different masses.

e.g.The atomic mass of chlorine is 35.5 u. Chlorine has

two isotopes Cl3517 and Cl3717 with abundance of 75%

and 25% respectively. Thus the average mass of a

chlorine atom will be 75% of 35 and 25% of 37, which

is 35.5 u.

So, Average atomic mass of chlorine

= 35 100

75+ 37

100

25

=100

2625+

100

925

=26.25 + 9.25

= 35.5 u.

Thus, the average atomic mass of chlorine is 35.5 u.

c) Applications of Radioactive Isotopes :

(i) In agriculture : Certain elements such asboron,

cobalt, copper, manganese, zinc and molybdenum

are necessary in very minute quantities for plant

nutrition. By radioactive isotopes we can identify the

presence and requirement of these element in the

nutrition of plants.

(ii) In industry :Isotopes are used for coating on the

arm of clock to see in dark. To identify the cracks in

metal casting.

(iii) In medicine :Thyroid, bone diseases, brain

tumors and cancer are controlled or destroyed with

the help of radioactive isotope P,Na, 321513153

2411 etc.

(iv) Determination of the mechanism of chemical

reaction by replacing an atom or molecule by its

isotopes.

(v) In carbon dating :Will and Libby (1960)developed

the technique of radiocarbon todetermine the age of

plant, fossil and archeological sample.

Note :

Isotopes (Like Uranium-238) are used in Nuclearreactor to produce energy and power.

ISOBARS

The atoms of different elements with different atomic

numbers, which have same mass number are called

isobars.

e.g. C146 and N147 are isobars.

Ar

40

18 and Ca

40

20

are

isobars.

Isobars

1. Atomic number 18 20

2. Mass number 40 40

3. No. of electrons 18 20

4. No. of protons 18 20

5. No. of neutrons 22 20

6. Electronic configuration 2, 8, 8 2, 8, 8, 2

Ar4018 Ca4020

Note

Isobars contain different number of electrons,protons and neutrons.

ISOTONES

Isotones may be defined as the atoms of different

elements containing same number of neutrons.

e.g. C136 and N147 (Both contain 7 neutrons)

Si3014 , P3115 and S

3216 (All three contain 16 neutrons)

ISOELECTRONIC

Ion or atom or molecule which have the same number

of electrons are called as isoelectronic species.

e.g. "Cl17

r184

K19

2

20Ca4

No. of electrons 18 18 18 18


15/59

PAGE # 13

ACIDS, BASES AND SALTS

ACIDS

Substances with sour taste are regarded as acids.

Lemon juice, vinegar, grape fruit juice and spoilt milketc. taste sour since they are acidic. Many substances

can be identified as acids based on their taste but

some of the acids like sulphuric acid have very strong

action on the skin which means that they are corrosive

in nature. In such cases it would be according to

modern definition -

An acid may be defined as a substance which

releases one or more H+ ions in aqueous solution.

Acids are mostly obtained from natural sources.

a) Classification of Acids :

(i) Classification of acids on the basis of their

Source

On the basis of their source, acids can be classified

in two categories :

(A) Organic acids (B) Inorganic acids

(A) Organic acids

The acids which are usually obtained from

organisms are known as organic acids. Oxalic acid

[(COOH)2], acetic acid (CH3COOH) etc. are very

common examples of organic acids. Some other

organic acids with their natural sources are given in

the following Table.

Some Organic Acids with Their Natural Sources

S.No. Organic acid Natural sources S.No. Organic acid Natural sources

1 Acetic acid Micro-organism 7 Oleic acid Olive oil

2 Citric acid Citrus fruits (like

orange and lemon)

8 Stearic acid Fats

3 Butyric acid Rancid butter 9 Amino acid Proteins

4 Formic acid Sting of bees and ants 10 Uric acid Urine

5 Lactic acid Sour milk 11 Tartaric acid Tamarind

6 Malic acid Apples 12 Oxalic acid Tomatoes

It may be noted that all organic acids contain carbon

as one of their constituting elements. These are weak

acids and, therefore, do not ionise completely in their

aqueous solutions. Since these acids do not ionise

completely in their aqueous solutions, therefore, their

solutions contains both ions as well as

undissociated molecules. For example, formic acids

aqueous solution contains H3O+, HCOOas well as

undissociated HCOOH molecules.

HCOOH + H2O H3O+ + HCOO

Formic acid Hydronium ion Formate ion

(B) Inorganic Acids.

The acids which are usually obtained from minerals

are known as inorganic acids. Since the acids are

obtained from minerals, therefore, these acids are

also called mineral acids. Some common examples

of inorganic acids are : Hydrochloric acid (HCl),

Sulphuric acid (H2SO4), Nitric acid (HNO3) etc.

It may be pointed out that except carbonic acid

(H2CO3), these acids do not contain carbon. Acids

like HCl, H2SO4 and HNO3 are strong acids which

ionise completely in their aqueous solutions and,

therefore, their aqueous solutions do not contain any

undissociated molecules.

(ii) Classification of acids on the basis of their

Basicity :

The basicityof an acid is defined as the number of

hydronium ions [H3O+(aq.)] that can be produced by

the complete ionisation of one molecule of that acid

in aqueous solution.

For example, basicity of HCl, H2SO4, H3PO4 is 1, 2

and 3 respectively because one molecule of these

acids, on ionisation, produces 1, 2 and 3 hydronium

ions in aqueous solution respectively.

It may be pointed out here that the basicity of an acidis determined by number of hydronium ions produced

per molecule of an acid on ionisation and not the

number of hydrogen atoms present in one molecule

of an acid. For example, basicity of acetic acid

(CH3COOH) is 1 because one molecule of acetic acid,

on ionisation in aqueous solution, produces one

hydronium ion although one molecule of acetic acid

contains four hydrogen atoms.

CH3COOH + H2O H3O+ + CH3COO

Acetic acid Hydronium ion Acetate ion

On the basis of basicity, the acids can be classifiedas under :


16/59

PAGE # 14

(A) Monobasic Acids :

When one molecule of an acid on complete ionisation

produces one hydronium ion (H3O+) in aqueous

solution, the acid is said to be a monobasic acid.

Examples of Monobasic Acids.

Some examples of monobasic acids are :

(i)Hydrochloric acid (HCl)

(ii) Hydrobromic acid (HBr)

(iii) Nitric acid (HNO3)

(iv)Acetic acid (CH3COOH)

(v) Formic acid (HCOOH)

Characteristics of Monobasic Acids.

Two important characteristics of monobasic acids

are :

(i)A monobasic acid ionises in one step in aqueous

solution. For example,

HCl + H2O H3O+ + Cl

(Single step ionisation)

(ii)A monobasic acid forms only single salt or a normal

salt. For example,HCl + NaOH ""# NaCl + H2O

Sodium chloride

(Normal salt)

(B) Dibasic Acids :


produces two hydronium ions (H3O+) in aqueous

solution, the acid is said to be a dibasic acid.

Examples of Dibasic Acids :

Some examples of dibasic acids are :

(i)Sulphuric acid (H2SO4)

(ii) Sulphurous acid (H2SO3)

(iii)Carbonic acid (H2CO3)(iv) Oxalic acid [(COOH)2]

(v) Hydrofluoric acid (HF)

Characteristics of Dibasic Acids :

Two important characteristics of dibasic acids are :

(i)A dibasic acid ionises in two steps in aqueous

solution. For example, sulphuric acid which is a dibasic

acid ionises to produce bisulphate ion (HSO4) in the

first step which further ionises to produce sulphate ion

(SO42) in the second step.

H2SO4 + H2O H3O++ HSO4

Sulphuric acid Bisulphate ion

HSO4 + H2O H3O

++ SO42

Sulphate ion

\ (ii) Because of the presence of two replaceable

hydrogen ions, a dibasic acid forms two series of salts

i.e., an acid salt and a normal salt. For example, H2SO4reacts with NaOH to form NaHSO4(an acid salt) and

Na2SO4(a normal salt)

NaOH + H2SO4""# NaHSO4+ H2OSodium hydrogen

sulphate

(An acid salt)

2NaOH + H2SO4""# Na2SO4+ 2H2O

Sodium sulphate(Normal salt)

(C) Tribasic Acids :


produces three hydronium ions (H3O+) in aqueous

solution, the acid is said to be a tribasic acid.

An example of tribasic acids is Phosphoric acid

(H3PO4).

(D) Tetrabasic Acids :

When one molecule of an acid on complete ionisationproduces four hydronium ions (H3O

+) in aqueous

solution, the acid is said to be a tetrabasic acid.

An example of tetrabasic acids is silicic acid (H4SiO4).

(iii) Classification of acids on the basis of their

strength :

We know that acids ionise in the aqueous solution to

produce hydronium ions. So, the strength of an acid

depends upon the degree of ionisation, usually

denoted by the letter alpha ($).Degree of ionisation of an acid ($)

=Number of molecules of the acid undergoing ionisation

100Total number of acid molecules %

More the degree of ionisation ($) of an acid, more strongerit will be. Generally, if the degree of ionisation ($) for anacid is greater than 30%, it is considered to be a strong

acid. If it is less than 30%,it is considered to be a weak

acid.

On the basis of degree of ionisation, the acids can be

classified as under:

(A) Strong Acids :

The acids which undergo almost complete ionisation

in a dilute aqueous solution, thereby producing a high

concentration of hydronium ions (H3

O+) are known as

strong acids.

Examples of strong acids :

Some examples of strong acids are :

(i) Hydrochloric acid (HCl)

(ii) Sulphuric acid (H2SO

4)

(iii) Nitric acid (HNO3)

All these three mineral acids are considered to be

strong acids because they ionise almost completely

in their dilute aqueous solutions.

(B) Weak Acids :

The acids which undergo partial or incomplete

ionisation in a dilute aqueous solution, therebyproducing a low concentration of hydronium ions

(H3O+)are known as weak acids.

Examples of weak acids :

Some examples of weak acids are :

(i) Acetic acid (CH3COOH)

(ii) Formic acid (HCOOH)

(iii) Oxalic acid [(COOH)2]

(iv) Carbonic acid (H2CO

3)

(v) Sulphurous acid (H2SO

3)

(vi) Hydrogen sulphide (H2S)

(vii) Hydrocyanic acid (HCN)

The aqueous solution of weak acids contain both ionsas well as undissociated molecules.


17/59

PAGE # 15

(iv) Classification on the basis of Concentration ofthe Acid :

By the term concentration, we mean the amount ofwater present in the given sample of acid solution inwater.

(A) Concentrated Acid :The sample of an acid which contains very small or noamount of water is called a concentrated acid.

(B) Dilute Acid :The sample of an acid which contains far more amountof water than its own mass is known as a dilute acid

It must be mentioned here that concentration of anacid simply tells the amount of water in the acid. It maynot be confused with strength of an acid, which is ameasure of concentration of hydronium ion it producesin aqueous solution.

A concentrated acid may not necessarily be a strongacid while a dilute acid may not necessarily be a weakacid. A strong acid will remain strong even if it is dilutebecause it produces a large concentration of hydronium

ions in aqueous solution. On the other hand, a weakacid will remain weak even when concentratedbecause it will produce lesser concentration ofhydronium ions in aqueous solution.

CHEMICAL FORMULAE, TYPES AND USES OF SOME COMMON ACIDS

Name Type Chemical Formula Where found or used

Carbonic acid Mineral acid H2CO3 In soft drinks and lends fizz.

Nitric acid Mineral acid HNO3

Used in the manufacture of explosives (TNT,

Nitroglycerine) and fertilizers (Ammonium nitrate,

Calcium nitrate, Purification of Au, Ag)

Hydrochloric acid Mineral acid HClIn purification of common salt, in textile industry

as bleaching agent, to make aqua regia, in

stomach as gastric juice, used in tanning industry

Sulphuric acid Mineral acid H2SO4

Commonly used in car batteries, in

the manufacture of fertilizers (Ammonium

sulphate, super phosphate) detergents etc, in

paints, plastics, drugs, in manufacture of artificial

silk, in petroleum refining.

Phosphoric acid Mineral acid H3PO4 Used in antirust paints and in fertilizers.

Formic acid Organic acid HCOOHFound in the stings of ants and bees, used in

tanning leather, in medicines for treating gout.

Acetic acid Organic acid CH3COOHFound in vinegar, used as solvent in the

manufacture of dyes and perfumes.

Lactic acid Organic acid CH3CH(OH)COOH Responsible for souring of milk in curd.Benzoic acid Organic acid C6H5COOH Used as a food preservative.

Citric acid Organic acid C6H8O7 Present in lemons, oranges and citrus fruits.

Tartaric acid Organic acid C4H6O6 Present in tamarind.

b) Chemical Properties of Acids :

(i) Action with metals :Dilute acids like dilute HCl and dilute H

2SO

4react with

certain active metals to evolve hydrogen gas.

2Na(s) + 2HCl (dilute) "#2NaCl(aq) + H2(g)

Mg(s) + H2SO

4(dilute)"#MgSO

4(aq) + H

2(g)

Metals which can displace hydrogen from dilute acidsare known as active metals. e.g. Na, K, Zn, Fe, Ca, Mgetc.

Zn(s) + H2SO

4(dilute) #ZnSO

4(aq) + H

2(g)

The active metals which lie above hydrogen in theactivity series are electropositive and more reactive innature. Their atoms lose electrons to form positive ionsand these electrons are accepted by H+ ions of theacid. As a result, H

2is evolved.

e.g.

Zn(s) #" Zn2+(aq) + 2e

2H+(aq) + SO4

2(aq) + 2e "# H2(g) + SO

42(aq)

Zn(s) + 2H

+

(aq)#"

Zn

++

(aq) + H2(g)

(ii) Action with metal oxides :

Acids react with metal oxides to form salt and water.These reactions are mostly carried out upon heating.e.g.

ZnO(s) + 2HCl (aq) "#" ZnCl2(aq) + H

2O(!)

MgO(s) + H2SO

4(aq) "#" MgSO

4(aq) + H

2O(!)

CuO(s) + 2HCl(aq.) "#" CuCl2(aq) + H2O(!)(Black) (Bluish green)

(iii) Action with metal carbonates and metalbicarbonates : Both metal carbonates and bicarbonatesreact with acids to evolve CO

2gas and form salts.

e.g.

CaCO3(s)+ 2HCl(aq) "#" CaCl

2(aq) + H

2O(!) + CO

2(g)

Calcium Calcium carbonate chloride

2NaHCO3(s) + H

2SO

4(aq) "#" Na

2SO

4(aq) + 2H

2O(aq) + 2CO

2(g)

Sodium Sodiumbicarbonate sulphate

(iv) Action with bases :Acids react with bases to give salt and water.

HCl (aq) + NaOH(aq) "#NaCl + H2O


18/59

PAGE # 16

BASE

Substances with bitter taste and soapy touch are

regarded as bases. Since many bases like sodium

hydroxide and potassium hydroxide have corrosive

action on the skin and can even harm the body, so

according to the modern definition -

A base may be defined as a substance capable of

releasing one or more OH ions in aqueous solution.

a) Alkalies :

Some bases like sodium hydroxide and potassium

hydroxide are water soluble. These are known as

alkalies. Therefore water soluble bases are known as

alkalies eg. KOH, NaOH.

Bases like Cu(OH)2, Fe(OH)

3and Al(OH)

3 these are

not alkalies.

A list of a few typical bases along with their chemical

formulae and uses is given below-

Name Commercial NameChemical

FormulaUses

Sodium hydroxide Caustic soda NaOHIn manufacture of soap, paper, pulp, rayon,

refining of petroleum etc.

Potassium hydroxide Caustic potash KOHIn alkaline storage batteries, manufacture of

soap, absorbing CO2gas etc.

Calcium hydroxide Slaked lime Ca(OH)2In manufacture of bleaching powder,

softening of hard water etc.

Magnesium hydroxide Milk of magnesia Mg(OH)2 As an antacid to remove acidity from stomach.

Aluminium hydroxide Al(OH)3 As foaming agent in fire extinguishers.

Ammonium hydroxide NH4OHIn removing grease stains from clothes and in

cleaning window panes.

b) Chemical Properties :

1. Action with metals :

Metals like zinc, tin and aluminium react with strong

alkalies like NaOH (caustic soda), KOH (caustic

potash) to evolve hydrogen gas.

Zn(s) + 2NaOH(aq)"#Na2ZnO

2(aq) + H

2(g)

Sodium zincate

Sn(s) + 2NaOH(aq)"#Na2SnO

2(aq) + H

2(g)

Sodium stannite

2Al(s)+ 2NaOH + 2H2O"#2NaAlO

2(aq) + 3H

2(g)

Sodium meta

aluminate

2. Action with non-metallic oxides :

Acids react with metal oxides, but bases react with

oxides of non-metals to form salt and water.

e.g.

2NaOH(aq) + CO2(g)"#Na

2CO

3(aq) + H

2O(!)

Ca(OH)2(s) + SO

2(g)

"#CaSO

3(s) + H

2O(!)

Ca(OH)2(s) + CO

2(g)"#CaCO

3(s) + H

2O(!)

CONDUCTING NATURE OF ACID

AND BASE SOLUTIONS

Acids are the substances which contain one or more

hydrogen atoms in their molecules which they can

release in water as H+ ions. Similarly, bases are the

substances which contain one or more hydroxyl groups

in their molecules which they can release in water as

OH ions . Since the ions are the carrier of charge

therefore, the aqueous solutions of both acids and

bases are conductors of electricity.

Experiment :

In a glass beaker, take a dilute solution of hydrochloric

acid (HCl). Fix two small nails of iron in a rubber cork in

the beaker as shown in the figure. Connect the nails to

the terminals of a 6 volt battery through a bulb. Switch

on the current and bulb will start glowing. This shows

that the electric current has passed through the acid

solution. As the current is carried by the movement of

ions, this shows that in solution HCl has ionised to

give H+ and Clions. Current will also be in a position

to pass if the beaker contains in it dilute H2SO

4(H+ions

are released in aqueous solution). Similarly, aqueous

solutions containing NaOH or KOH will also be

conducting due to release of OHions.

Battery Bulb incircuit

Switch

Dilute HCl

Iron Nails

Rubber cork

Bulb will not glow if glucose (C6H

12O

6) or ethyl alcohol

(C2H

5OH) solution is kept in the beaker. This means

that both of them will not give any ions in solution.


19/59

PAGE # 17

Acids Bases

Sour in taste. Bitter in taste.

Change Colours of indicators

e.g. litmus turns from blue to

red, phenolphthalein remains

colourless.

Change colours of indicators e.g.

litmus turns from red to blue

phenolphthalein turns from

colourless to pink.

Show electrolytic conductivity

in aqueous solution.

Show electrolytic conductivity in

aqueous solution

Acidic properties disappear

when react with bases

(Neutralization)

Basic properties disappear when

react with acids (Neutralization)

Acids decompose carbonate

salts.

No decomposition of carbonate

salts by bases

ROLE OF WATER IN THE IONISATION

OF ACIDS AND BASES

Substances can act as acids and bases only in the

presence of water (in aqueous solution). In dry state

which is also called anhydrous state, these characters

cannot be shown. Actually, water helps in the ionisation

of acid or base by separating the ions. This is also

known as dissociation and is explained on the basis

of a theory called Arrhenius theory of acids and bases.

In the dry state, hydrochloric acid is known as hydrogen

chloride gas i.e. HCl(g). It is not in the position to give

any H+ ions. Therefore, the acidic character is not

shown. Now, let us pass the gas through water taken

in a beaker with the help of glass pipe. H2O molecules

are of polar nature which means that they have partial

negative charge (&) on oxygen atom and partial positive

charge (&+) on hydrogen atoms. They will try to form asort of envelope around the hydrogen atoms as well

as chlorine atoms present in the acid and thus help in

their separation as ions. These ions are said to be

hydrated ions.

HCl(g) + H2O"# H

3O++ Cl(aq)

(Hydrated ions)

The electrical current is carried through these ions.

The same applies to other acids as well as bases.

Thus we conclude that -

(i)acids can release H+ions only in aqueous solution.

(ii)base can release OH

ions only in aqueous solution.(iii)hydration helps in the release of ions from acids

and bases.

DILUTION OF ACIDS AND BASES

Acids and bases are mostly water soluble and can be

diluted by adding the required amount of water. With

the addition of water the amount of acid or base per

unit volume decrease and dilution occurs. The process

is generally exothermic in nature. When a concentrated

acid like sulphuric acid or nitric acid is to be diluted

with water, acid should be added dropwise to water

taken in the container with constant stirring.

THEORIES OF ACIDS AND BASES

a) Arrhenius Theory :

This concept was given in 1884 .

According to this theory all substances which give H+

ions when dissolved in water are called acids, while

those which ionise in water to give OH ions are called

bases.The main points of this theory are -

(i)An acid or base when dissolved in water, splits intoions. This is known as ionisation.

(ii)Upon dilution, the ions get separated from each other.This is known as dissociation of ions.

(iii) The fraction of the acid or base which dissociatesinto ions is called its degree of dissociation and isdenoted by alpha '$(which can be calculated by thefollowing formula :

$=moleculesofno.total

mequilibriuatddissociatemoleculesofNo.

(iv)The degree of dissociation depends upon the nature

of acid or base. Strong acids and bases are highlydissociated, while weak acids and bases aredissociated to lesser extent.

(v)The electric current is carried by the movement ofions. Greater the ionic mobility more will be theconductivity of the acid or base.

(vi) The H+ ions do not exist as such and exist incombination with molecules of H

2O as H

3O+ ions

(known as hydronium ion).

H++ H2O H

3O+

HCl + H2O H

3O++ Cl

e.g.

HA + H2O H3O++ AAcid

H2SO

4+ 2H

2O 2H

3O++ SO

42

Acid

BOH Water B++ OH

Base

NaOH Water Na++ OH

Base

NH4OH Water NH

4++ OH

Base

(A) Limitations of Arrhenius theory :

It is applicable only to aqueous solutions. For the

acidic or basic properties, the presence of water isabsolutely necessary.

The concept does not explain the acidic or basicproperties of acids or bases in non - aqueous solvents.

It fails to explain the basic nature of compounds like

NH3, Na

2CO

3 etc., which do not have OH in their

molecules to furnish OH ions.

It fails to explain the acidic nature of non - proticcompounds like SO

2, P

2O

5, CO

2, NO

2etc., which do not

have hydrogen in their molecules to furnish H+ions.

It fails to explain the acidic nature of certain salts likeAlCl

3etc., in aqueous solutions.


20/59

PAGE # 18

b) Acid Base Concept of Bronsted and

Lowry :

This theory was given by Bronsted, a Danish chemistand Lowry, an English chemist independently in 1923.According to it, an acid is a substance, molecule or ionwhich has a tendency to release the proton(protogenic) and similarly a base has a tendency toaccept the proton (protophilic).

e.g.

HCl + H2O H

3O++ Cl

In this reaction, HCl acts as an acid because it donatesa proton to the water molecule. Water, on the otherhand, behaves as a base by accepting a proton.

Note :Bronsted and Lowry theory is also known as protondonor and proton acceptor theory.

Other examples :

(i) CH3COOH + H

2O H

3O++ CH

3COO

(ii) NH4

++ H2O H

3O++ NH

3

(iii) NH3+ H

2O NH

4++ OH

In the reactions (i) and (ii) water is acting as a base,

while in reaction (iii) it is acting as an acid.Thus water

can donate as well as accept H+and hence can act as

both acid and base.

Note :

The species like H2O, NH

3, CH

3COOH which can act

as both acid and base are called amphiprotic.

Moreover according to theory, an acid on losing a

proton becomes a base, called conjugate base, while

the base by accepting proton changes to acid called

conjugate acid.

Here CH3COO ion is conjugate base of CH

3COOH,

while H3O+ion is conjugate acid of H

2O.

(i) Merits :

(A) Besides water any other solvent, which has the

tendency to accept or lose a proton may decide the

acidic or basic behaviour of the dissolved substance.

(B)This theory states that the terms acid and base are

comparative. A substance may act as an acid in one

solvent, while as a base in another solvent.

e.g. Acetic acid acts as an acid in water while as a

base in HF.

(ii) Demerits :

(A) Many acid - base reactions proceed without H+

transfer.

e.g.SO2

+ SO3

SO2+ + SO4

2-

c) Lewis theory :

The theory was given by G.N. Lewis in 1938. Accordingto it, an acid is a species which can accept a pair ofelectrons, while the base is one which can donate apair of electrons.

Note :It is also known as electron pair donor and electron

pair acceptor theory.

e.g.(i)FeCl

3and AlCl

3are Lewis acids, because the central

atoms have only six electrons after sharing and needtwo more electrons.

(ii)NH3 is a Lewis base as it has a pair of electrons

which can be easily donated.Lewis acids :- CH

3+, H+, BF

3, AlCl

3, FeCl

3etc.

Lewis base :-NH3, H

2O, ROR, R OH, CN, OH

etc.

(i) Characteristics of species which can act as Lewis

acids :

(A) Molecules in which the central atom has

incomplete octet :Lewis acids are electron deficientmolecules such as BF

3, AlCl

3, GaCl

3etc.

H N + AlCl3 3 [HN3 AlCl ]3

(B) Molecules in which the central atom has emptyd-orbitals : The central atom of the halides such asTiCl

4, SnCl

4, PCl

3, PF

5, SF

4, TeCl

4. etc., have vacant d-

orbitals. These can, therefore, accept an electron pairand act as Lewis acids.

(C) Simple cations :All cations are expected to act asLewis acid, since they are electron deficient in nature.

(D) Molecules having a multiple bond betweenatoms of dissimilar electronegativity : Typicalexamples of molecules belonging to this class ofLewis acids are CO

2, SO

2and SO

3.

(ii) Characteristics of species which can act as Lewisbases :

(A) Neutral species having at least one lone pair ofelectrons : For example, ammonia amines, alcoholsetc, act as Lewis bases as they contain a pair ofelectrons.

(B) Negatively charged species or simple anions :For example chloride (Cl), cyanide (CN), hydroxide(OH) ions etc. act as Lewis bases.

(C) Multiple bonded compounds :The compoundssuch as CO, NO, ethylene, acetylene etc. can act asLewis bases.

Note :It may be noted that all Bronsted bases are also Lewis

bases, but all Lewis acids are not Bronsted acids.

(iii) Limitations of Lewis theory :

(A)Lewis theory fails to explain the relative strength ofacids and bases.


21/59

PAGE # 19

INDICATORS

, An indicator indicates the nature of a particular solution

whether acidic, basic or neutral. Apart from this, indicator

also represents the change in nature of the solution

from acidic to basic and vice versa. Indicators are

basically coloured organic substances extracted from

different plants. A few common acid base indicators are-

a) Litmus :

Litmus is a purple dye which is extracted from lichen

a plant belonging to variety Thallophyta. It can also be

applied on paper in the form of strips and is available

as blue and red strips. A blue litmus strip, when dipped

in an acid solution acquires red colour. Similarly a red

strip when dipped in a base solution becomes blue.

b) Phenolphthalein :

It is also an organic dye and acidic in nature. In neutral

or acidic solution, it remains colourless while in the

basic solution, the colour of indicator changes to pink.

c) Methyl Orange :

Methyl orange is an orange or yellow coloured dye and

basic in nature. In the acidic medium the colour of

indicator becomes red and in the basic or neutral

medium, its colour remains unchanged.

d) Red Cabbage Juice :

It is purple in colour in neutral medium and turns red

or pink in the acidic medium. In the basic or alkaline

medium, its colour changes to green.

e) Turmeric Juice :

It is yellow in colour and remains as such in the neutral

and acidic medium. In the basic medium its colour

becomes reddish or deep brown.

Note :

Litmus is obtained from LICHEN plant.

NEUTRALISATION

It may be defined as a reaction between acid and

base present in aqueous solution to form salt and

water.HCl(aq) + NaOH(aq)"#NaCl(aq) + H

2O(!)

Basically neutralisation is the combination between

H+ions of the acid with OH

ions of the base to form H2O.

e.g.

H+(aq) + Cl

(aq) + Na+(aq) + OH

(aq)"#Na+(aq) + Cl(aq) + H2O(!)

H+(aq) + OH(aq)"#H

2O(!)

Neutralisation reaction involving an acid and base is

of exothermic nature. Heat is evolved in all

neutralisation reactions. If both acid and base are

strong, the value of heat energy evolved remains same

irrespective of their nature.

e.g .

HCl (aq) + NaOH (aq) "#" NaCl (aq) + H2O (!) + 57.1 KJ

Strong Strong

acid base

HNO3(aq) + KOH (aq) "#" KNO

3(aq) + H

2O (!) + 57.1 KJ

Strong Strong

acid base

Strong acids and strong bases are completely ionised

of their own in the solution. No energy is needed for

their ionisation. Since the cation of base and anion of

acid on both sides of the equation cancel out

completely, the heat evolved is given by the following

reaction -

H+(aq) + OH(aq) "#" H2O (!) + 57.1 KJ

APPLICATIONS OF NEUTRALISATION

(i) People particularly of old age suffer from acidity

problems in the stomach which is caused mainly due

to release of excessive gastric juices containing HCl.The acidity is neutralised by antacid tablets which

contain sodium hydrogen carbonate (baking soda),

magnesium hydroxide etc.

(ii) The stings of bees and ants contain formic acid. Its

corrosive and poisonous effect can be neutralised by

rubbing soap which contains NaOH (an alkali).

(iii) The stings of wasps contain an alkali and its

poisonous effect can be neutralised by an acid like

acetic acid (present in vinegar).

(iv)Farmers generally neutralize the effect of acidity in

the soil caused by acid rain by adding slaked lime

(Calcium hydroxide) to the soil.

According to Arrhenius theory, an acid releases H+ion

in aqueous solution. The concentration of these ions

is expressed by enclosing H+in square bracket i.e. as

[H+]. Thus, greater the [H+] ions, stronger will be the

acid. However, according to pH scale, lesser the pH

value, stronger will be the acid. From the above

discussion, we can conclude that pH value and H+ion

concentration are inversely proportional to each other.

The relation between them can also be expressed as-

pH = log [H+] = log )*

+,-

./H

1

So, negative logarithm of hydrogen ion concentration

is known as pH.

e.g.

Let the [H+] of an acid solution be 103M. Its pH can be

calculated as -

pH = log [H+]

= log [103]

= () (3) log 10

= 3 ("log 10 = 1)


22/59

PAGE # 20

Note :

Just as the [H+] of a solution can be expressed in terms

of pH value, the [OH] can be expressed as pOH.

Mathematically , pOH = log [OH] = log]OH[

1

Moreover, pH + pOH = 14.

Thus, if pH value of solution is known, its pOH value

can be calculated.

Note :There are some solutions which have definite pH i.e.,

their pH do not change on dilution or on standing for

long. Such solutions are called buffer solutions.

Ex.1Calculate the concentration of H3O+ions and OHions

in (a) 0.01 M solution of HCl (b) 0.01 M solution of

NaOH at 298 K, assuming that HCl and NaOH are

completely ionized under the given conditions.

Sol. (a) HCl(aq) + H2O(l) H3O

+(aq) + Cl(aq)

Since HCl is completely ionized

0[H3O+] = [HCl] = 0.01 M

or 1 102

mol L1

[OH] =]OH[

]K[

3

w

/

= 2

14

101

101

%

%1 10 12 mol L1

(b) NaOH(aq)"#Na+(aq) + OH(aq)Since NaOH is completely ionized

[OH] = [NaOH] = 0.01 M

or 1 102mol L1

[H3O+] = ]OH[

K

w

= 2

14

101

101

%

%

= 1 1012mol L1.

Ex-2Calculate the concentration of H3O+ ions and pH in

0.005 M solution of Ba(OH)2at 298 K, assuming that

Ba(OH)2

is completely ionized under the given

conditions.

Sol. Ba(OH)2(aq) "#Ba2+(aq) + 2OH(aq)

Since Ba(OH)2is completely ionized and on ionization

its one molecule gives two OHions.

0[OH] = 2[Ba(OH)2]

= 2 0.005 = 0.01 mol L1

= 1 102mol L1

[H3O+] =

]OH[

K

w= 2

14

101

101

%

%

= 1 1012mol L1

pH = 12

SALTS

A substance formed by neutralization of an acid

with a base is called a salt.

e.g.

Ca(OH)2(aq)+ H

2SO

4(aq) # CaSO

4(aq) + 2H

2O(!)

Cu(OH)2(aq) + 2HNO3(aq) #Cu(NO3)2(aq) + 2H2O(!

)NaOH(aq) + HCl(aq) #NaCl(aq) + H

2O(!)

a) Classification of Salts :

(i) It is based on their Mode of Formation :

(A) Normal Salts :

The salts which are obtained by complete replacementof the ionisable hydrogen atoms of an acid by a metallicor an ammonium ion are known as normal salts. Forexample, normal salts NaCl and Na2SO4are formed

by the complete replacement of ionisable hydrogenatoms of HCl and H2SO4respectively

HCl + NaOH ""# NaCl + H2O Sodium chloride (Normal salt)

H2SO4 + 2NaOH ""# Na2SO4 + 2H2O Sodium sulphate (Normal salt)

Some of the salts are given below in the table.

S.No. Parent Acid Normal Salts

1

Hydrochloric acid

(HCl)

NaCl, KCl, MgCl2, AlCl3, ZnCl2,

CaCl2and NH4Cl .

2Nitric acid

(HNO3)

NaNO3, KNO3, Mg(NO3)2,Al(NO3)3,

Zn(NO3)2, Ca(NO3)2.

3Sulphuric acid

(H2SO4)

Na 2SO4, K2SO4, MgSO4, Al2(SO4)3,

ZnSO4, CaSO4.

4Acetic acid

(CH 3COOH)

CH 3COONa, CH3COOK, (CH3COO)2Ca,

(CH3COO)2Pb, CH3COONH4.

5Carbonic acid

(H2CO3)

Na 2CO3, K2CO3, MgCO3, ZnCO3,

CaCO3, (NH4)2CO3.

6Sulphurous acid

(H2SO3)

Na 2SO3, K2SO3, MgSO3, ZnSO3,

CaSO3, (NH4)2SO3.

7Phosphoric acid

(H3PO4)

Na 3PO4, K3PO4, Mg3(PO4)2,

Zn3(PO4)2, Ca3(PO4)2, (NH4)3PO4.

Some Exam ples of Normal Salts with their Parent Acids :

(B) Acid Salts : The salts which are obtained by thepartial replacement of ionisable hydrogen atoms of apolybasic acid by a metal or an ammonium ion areknown as acid salts.

These are usually formed when insufficient amount ofthe base is taken for the neutralisation of the acid. Forexample, when insufficient amount of NaOH is takento neutralise H2SO4, we get an acid salt NaHSO4.H2SO4 + NaOH ""# NaHSO4 + H2O

(Insufficient amount) Sodium hydrogensulphate

(Acid salt)

In this case, only one hydrogen atom out of two has

been replaced by sodium atom. Since there is onemore hydrogen atom in NaHSO4 which can bereplaced, therefore, it further reacts with anothermolecule of NaOH to produce Na2SO4 which is anormal salt.

NaHSO4 + NaOH # Na2SO4 + H2OSodium Sodium

hydrogensulphate sulphate(Acid salt) (Normal salt)

Acid salts ionise in aqueous solution to produce

hydronium ions (H3O+), therefore, they exhibit all the

properties of acids.


23/59

PAGE # 21

Some other examples of acid salts are given in Table.

SOME ACID SALTS WITH THEIR PARENT ACIDS

S.No. Parent Acid Acid Salts

1

Sulphuric acid

(H2SO4)

NaHSO4, KHSO4,

Ca(HSO4)2

2

Carbonic acid

(H2CO3)

NaHCO3, KHCO3,

Ca(HCO3)2, Mg(HCO3)2

3

Sulphurous acid

(H2SO3)

NaHSO3, KHSO3,

Ca(HSO3)2, Mg(HSO3)2

4

Phosphoric acid

(H3PO4)

NaH2PO4, Na2HPO4, KH2PO4,

K2HPO4, Ca(H2PO4)2, CaHPO4

(C) Basic Salts : The salts which are formed by partial

replacement of hydroxyl (OH) groups of a di-or a

triacidic base by an acid radical are known as basic

salts.

These are usually formed when an insufficient amount

of acid is taken for the neutralisation of the base. For

example, when insufficient amount of HCl is added toLead hydroxide, Basic lead chloride [Pb(OH)Cl] is

formed

Pb(OH)2 + HCl ""# Pb (OH)Cl + H2OLead hydroxide Basic Lead chloride

(Diacidic base) (Basic salt)

Basic salts, for example, Pb(OH)Cl further reacts with

HCl to form normal salts

Pb (OH) Cl + HCl ""# PbCl2 + H2OBasic Lead Chloride Lead chloride

(Basic salts) (Normal salt)

Some other important examples of basic salts are :

(i) Basic copper chloride, Cu(OH)Cl.

(ii) Basic copper nitrate, Cu(OH)NO3(iii) Basic lead nitrate, Pb(OH)NO3.

(D) Double Salts : The salts which are obtained by the

crystallisation of two simple salts from a mixture of

their saturated solutions are known as double salts.

For example, a double salt potash alum [K2SO4.

Al2(SO4)3. 24H2O] is prepared by mixing saturated

solutions of two simple salts, K2SO4and Al2(SO4)3and

crystallization of the mixture.

K2SO4 + Al2(SO4)3+ 24H2OCrystallisation""""""# K2SO4. Al2(SO4)3. 24 H2O

Potassium Potash alum

sulphate (Double salt)

Some other examples of double salts are :

(i) Mohrs Salt, FeSO4.(NH4)2SO4. 6H2O,

(ii) Dolomite, CaCO3. MgCO3,

(iii) Carnallite, KCl. MgCl2.6H2O

(E) Mixed Salts : The salts which contain more than

one type of acidic or basic radicals are called mixed

salts. For example, Sodium potassium carbonate

(NaKCO3) is a mixed salt containing two basic radicals

sodium and potassium. Similarly, calcium oxy chloride,

Ca(OCI)Cl is also a mixed salt containing two acid

radicals OCIand Cl.

Some other important examples of mixed salts are :

Sodium potassium sulphate (NaKSO4) (containing two

basic radicals), Disodium potassium phosphate

(Na2KPO4) (containing two basic radicals).

(ii) Classification of salt solutions based on pH

values :

Salts are formed by the reaction between acidsand bases. Depending upon the nature of the acids

and bases or upon the pH values, the salt solutions

are of three types.

(A) Neutral salt solutions : Salt solutions of strong

acids and strong bases are neutral and have pH equal

to 7. They do not change the colour of litmus solution.

e.g. NaCl, KCl, NaNO3, Na

2SO

4etc.

(B) Acidic salt solutions : Salt solutions of strong ac-

ids and weak bases are of acidic nature and have pH

less than 7. They change the colour of blue litmus

solution to red.

e.g.(NH4)2SO4, NH4Cl etc.In both these salts, the base NH

4OH is weak while the

acids H2SO

4and HCl are strong.

(C) Basic salt solutions : Salt solutions of strong bases

and weak acids are of basic nature and have pH more

than 7. They change the colour of red litmus solution to

blue.

e.g.Na2CO

3, K

3PO

4etc.

In both the salts, bases NaOH and KOH are strong

while the acids H2CO

3and H

3PO

4are weak.

Some Important Chemical Compounds :

Common name : Table Salt

Chemical name : Sodium chloride

Chemical formula : NaCl

Sodium chloride (NaCl) also called common salt or

table salt is the most essential part of our diet. Chemi-

cally it is formed by the reaction between solutions of

sodium hydroxide and hydrochloric acid. Sea water is

the major source of sodium chloride where it is present

in dissolved form along with other soluble salts such

as chlorides and sulphates of calcium and magne-

sium. It is separated by some suitable methods. De-

posits of the salts are found in different parts of the

world and is known as rock salt. When pure, it is awhite crystalline solid, however, it is often brown due to

the presence of impurities.

Uses :

(i) Essential for life : Sodium chloride is quite essen-

tial for life. Biologically, it has a number of functions to

perform such as in muscle contraction, in conduction

ntse chemistry

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