topic: date liquid state-1 - 06/04/202020 only y use e · intermolecular force the intermolecular...

Programme: B.Sc. B.ed. (Integrated) Course: States of Matter and Nuclear ChemistryChemistry

Semester: II Code: CHE-151

Topic: Liquid state-1Date- 06/04/2020

Dr. Angad Kumar Singh Department of ChemistryDepartment of Chemistry,

Central University of South Bihar, Gaya (Bihar)

Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia.


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Liquid StateIn solid the constituent particles (atoms, ions or molecule) are closely packed.

Hence they possess rigidity and have a definite volume and shape.

In gases, the particles are completely free to move. They have neither definite

shape nor volume. They fill up the vessel of any volume and also takep y p y

up the shape of that vessel.

In a liquid the particle are not fixed as in solid, and the same time, they haveIn a liquid the particle are not fixed as in solid, and the same time, they have

some freedom of motion though they are not as free to move as in

gas Thus liquid show behavior in between that of gas and that ofgas. Thus liquid show behavior in between that of gas and that of

solid


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Like solid liquid have a definite volume where as unlike solids

but like gases the do not have a definite shape.

They take up the shape of the vessel in which they are put.

The term isotropic is used to explain the properties of the matterp p p p

in basic crystallography.

A true liquid is isotropic, meaning that its properties (optical-A true liquid is isotropic, meaning that its properties (optical

and other properties such as thermal and electrical conductivity) are

uniform in all directions— the result of its molecules being in constantuniform in all directions— the result of its molecules being in constant

random motion. Thi i d b i th t li id t t i i t i dThis is expressed by saying that liquid state is isotropic and

intermediate between gaseous state and solid state.


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Intermolecular force

The intermolecular distance

• Solid-particles are much closedp

• Liquid- particles have small distance

• Gas- intermolecular distance so largeGas intermolecular distance so large

The intermolecular distances suggest that the cohesive force

(intermolecular force of attraction)(intermolecular force of attraction)

Cohesive force in

S lid• Solid- very strong

• Gas-very weak

• Liquid- are in between i.e. they are fairly strong to keep them in the

condensed state but not strong enough to hold them in fixed positions


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In fact, all the characteristic properties of liquids such as a, p p f q

vapour pressure, surface tension, viscosity etc arise due to the nature of

the cohesive force existing in the liquids.the cohesive force existing in the liquids.

These forces (cohesive force) are three types-

(1) Dipole dipole attraction(1) Dipole- dipole attraction-

• Occur among the polar molecules

P l l l h t di l• Polar molecules have permanent dipoles

The positive pole of one molecule is thus attracted by negative

pole of other molecule

For example HCl


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(2) Dipole induced dipole attraction(2) Dipole- induced dipole attraction-

The positive end of a polar molecule may attract the electron

l d f l l l l i l i Th l l lcloud of non-polar molecule lying close to it. Thus non-polar molecule

become polar, for example iron peace is brought close to a magnate

The attraction between polar molecule (permanent dipole) and

non-polar molecule (induced dipole).


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(3) Induced dipole induced dipole attraction (London force or(3) Induced dipole- induced dipole attraction (London force or

dispersive forces)-

It i t i i i tt ti i di l tt ti dIt is easy to conceive ion-ion attractions, ion-dipole attractions and

dipole-dipole attraction.

What intermolecular forces attract non-polar molecules to each

other in liquid and solid state?

These forces are thought to arise from motion of electrons. At any

instant time, the electron cloud of molecule may be distorted so that

momentary dipole is produced in which one part of molecule is slightly

more negative than the rest. The momentary dipoles induce dipole in the

neighbouring molecules. They are attracted to each other exactly in the

same way as permanent dipoles.y p p


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The force of attraction between the induced momentary dipoles

are called London forces (weakest intermolecular force)

Van der Waal’s forces is general term which imply that all types

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Topic: Structure of liquidsDate- 08/04/2020





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Structure of liquidsStructure of liquidsHow constituent particles are arranged within the liquid ?

The following different studies help in to know about the

structure of liquid

(1) Volume changes on fusion and vaporization-

when a pure solid melts, (some disorder has been introduced) the

increases in volume is only about 1% which much smaller than

increases in volume which takes place when the liquid changes

into vapour (large disorder has been introduced) at the boiling

point ( which is about 100-1000 times). Hence we conclude thatp ( )

the constituent particle of a liquid are not as ordered as that in a

solid but at same time they are not as disorder as that in a gassolid but at same time, they are not as disorder as that in a gas.


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(2) Enthalpy of fusion and vaporization-

Amount of heat required to melt one mole of a pure solid at

melting point (�Hf) is found to be much smaller than the amount ofg p ( f)

heat required to convert one mole of liquid into vapour at boiling point

(�H )(�Hvap).

for example Ice, �Hf=6.1 kJmol-1 and water (�Hvap)= 40.7 kJmol-1

Hence we conclude that greater the amount of heat absorbed greater isHence we conclude that greater the amount of heat absorbed, greater is

the disorder introduced.

(3) X R diff i d(3) X-Ray diffraction study-

X-Ray diffraction studies of crystalline solid show that

particles are arranged perfectly and extends upto the edge of the crystal

(long range order)


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• Solid (long range order)• Solid (long range order)

• Gas (No order)

Li id ( h t d )• Liquid (short range order)

Models of liquids state

In case of solid the cohesive force are very strong which keep

vibrational energy

In case of liquid the cohesive force are sufficiently strong so that

they can exist in the condensed state but not strong enough to hold the

particles in the fixed position so that they have some translational energy.

The two common theories about liquids

(1) Vacancy or hole theory proposed by erring and Ree theory

Liquid can be considered to consist of liquid “molecules” andq q

“holes” randomly distributed between themNote: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia.

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Due to presence of holes, the neighbouring molecules can easilyp , g g y

jump into them and thus show “gas-like” behavior, those molecules which

do not have a hole in the neighbourhood cannot jump and hence showdo not have a hole in the neighbourhood cannot jump and hence show

“solid –like” behavior.

(2) Free volume theory(2) Free volume theory-

according to this theory, it is believed that a molecule in a liquid

i d d b 10 12 i hb i l l l ll diis surrounded by 10-12 neighbouring molecules, only a small distance

away from the molecule.Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia.

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Thus surrounding molecule thus form a cage or cell around the

central moleculecentral molecule

Thus the central molecule has to move only a small distance to

llid ith f th i hb i l lcollide with any of the neighbouring molecule.

Thus the centre of the caged molecule can move within the

h b h h d d h l h il blspace shown by the shaded area. The volume thus available to a

molecule can moves are called as free volume.


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Topic: COLLOIDALDate- 10/04/2020





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COLLOIDAL

A colloid (from Greek, kolla meaning glue-like), or disperse

phase, is a dispersion of small (something less than about 500 nm)phase, is a dispersion of small (something less than about 500 nm)

particles of one material in another..

A colloidal system in thus a two phase consisting of aA colloidal system in thus a two phase consisting of a

continuous phase or dispersion medium in which extremely minute

ti l l i ithi th ll id l d d di tiparticles lying within the colloidal range and second discontinuous

phase or dispersed phase are suspended.

In general, colloidal particles are aggregates of numerous

atoms or molecules, but are too small to be seen with an ordinary

optical microscope. They pass through most filter papers, but can be

detected by light scattering and sedimentation


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ClassificationClassificationThe name given to the colloid depends on the two phases

involvedinvolved.

Sol(a system with solid dispersed phase and a liquid as

dispersion medium (such as clusters of gold atoms in water) or of adispersion medium (such as clusters of gold atoms in water) or of a

solid in a solid (such as ruby glass, which is a gold-in-glass sol, and

hi it l b li ht tt i )achieves its colour by light scattering).

Aerosol, when dispersion medium is a gas and dispersed

phase is liquid (like fog and many sprays) or a solid in a gas (such as

smoke): the particles are often large enough to be seen with a

microscope.

An emulsion is a dispersion of a liquid in a liquid (such as milk).


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A further classification of colloids is as lyophilic, or solvent

attracting, and lyophobic, solvent repelling.attracting, and lyophobic, solvent repelling.

If the solvent is water, the terms hydrophilic and

hydrophobic respectively are used instead Lyophobic colloidshydrophobic, respectively, are used instead. Lyophobic colloids

include the metal sols.

L hili ll id ll h h i l i il it tLyophilic colloids generally have some chemical similarity to

the solvent, such as -OH groups able to form hydrogen bonds.

A gel is a semi-rigid mass of a lyophilic sol in which all the

dispersion medium has penetrated into the sol particles.


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PROPERTIES OF COLLOIDS

The properties of colloids are discussed under three types

i. Kinetic property

ii. Optical property

iii. Electrical property

Kinetic propertyKinetic propertyWhen sol is examined with an ultramicrosope, the suspended

particles are seen as shining specks (a tiny spot) of light By followingparticles are seen as shining specks (a tiny spot) of light. By following

an individual particle, it is observed that the particle is undergoing a

id i I i i h i h li h iconstant rapid motion. It moves in a series short straight line paths in

the medium, changing direction abruptly(unexpectedly).


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The continuous rapid zig zag chaotic random and ceaselessThe continuous rapid zig-zag chaotic random and ceaseless

movement executed by a colloidal particle in the dispersion medium is

ll d b i Thi i d h b l d b b dcalled brownian movement. This is due to the unbalanced bombardment

of the particles by the molecules of the dispersion medium.

Optical property

When a strong beam of light is passed through a sol and viewed

at right angles, the path of light shows up as a hazy beam.g g , p g p y


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This is due to the fact that sol particles absorb light energy and

then emit it in all directions. This scattering of light illuminates the path

of the beam. The phenomenon of the scattering of light by the sol

particles is called Tyndall effect.

Under the Tyndall effect, the longer wavelengths areUnder the Tyndall effect, the longer wavelengths are

more transmitted while the shorter wavelengths are more diffusely

reflected via scattering.reflected via scattering.


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It is partic larl applicable to colloidal mi t res and fineIt is particularly applicable to colloidal mixtures and fine

suspensions; for example, the Tyndall effect is used in nephelometers to

d h d d f l l d h ll d ldetermine the size and density of particles in aerosols and other colloidal

matter (ultramicroscope and turbidimeter).

Electrical Properties

(i) Charge on Colloidal particles

The important property of colloidal dispersions is that all the

suspended particles possess either a positive or negative charge.

The mutual forces of repulsion between similarly charged

particles prevent them from aggregating and settling under the action of

gravity. This gives stability to the sol.g av ty. his gives stability to the sol.


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Topic: Electrical double layer(EDL) TheoryDate- 12/04/2020





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The surface of colloidal particle acquires a positive charges byThe surface of colloidal particle acquires a positive charges by

selective adsorption of a layer of positive ions around it. This layer attracts

counter ions from the medium which form a second layer of negativecounter-ions from the medium which form a second layer of negative

charges. The combination of the two layers of charges around the sol

particle is called Helmholtz double layerparticle is called Helmholtz double layer.Electrical double layer(EDL) Theory1. When electrode immersed in an electrolytic solution, charge. W e e ect ode e sed a e ect o yt c so ut o , c a ge

accumulation will occur.

2. Particle size should be greater than 1 nm.g

3. Charge separation always occurs at the interface of the electrodes in

the solution.

4. The excess charge on the electrode surface is accumulated by an

accumulation of the excess ions of the opposite charge in solution.pp g


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EDL is a transition region between two phasesEDL is a transition region between two phases

consist of ,

1. An inner molecular layer1. An inner molecular layer

2. A outer diffuse region

3. A layer intermediate between inner molecular3. A layer intermediate between inner molecular

layer and the outer diffuse region

An electrical double layer consists of two parts;

(1) One part of the double layer, known as fixed part (STERN LAYER)

remains almost fixed to the solid surface. It has positive or negative ions.

There is a sharp fall of potential.

(2) The second part of the double layer, known as diffuse part (DIFFUSE

LAYER) extends to some distance into the liquid phase.


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Diffuse layer contains ions of both signs. Its net charge is equal and opposite to that on the fixed part.

STERN LAYER•Also known as the Stationary Layer •Occurs in next to the surface of the

DIFFUSE LAYER• Occurs next to the Stern layer. • This layer is called as bulk liquid

particle.• Ions are bound to the surface very

y qlayer.• Occurs in between the stern layer

firmly. •Occurs due to the absorbing and

coulomb interaction

and the bulk.• Both positive and negative

charges can be seencoulomb interaction. charges can be seen


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ZETA POTENTIALC t b d EDLConcepts based on EDL

� It is a parameter of equilibrium on interface.

� It is depend on: (a) Properties of liquid and surface. (b) Electrostatic

repulsion between particle.

� High zeta potential value – stronger repulsion, the more stable

colloidal system.

� Example- fat droplet in milk has high zeta potential. Because prevent

against coalescence. In chees formation adds acid to prevent from

coalescence.

� The value of zeta potential cannot be measured directly fromp y

experimentally.


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�Zeta potential measure the�Zeta potential measure the

effectiveness of surface charge of

the electrical double layerthe electrical double layer.

�Zeta potential uses to estimate of

St t ti l d th iStern potential and the main

characteristics of the electrostatic

repulsion preventing particles

aggregation.

�Uses of zeta potential is to study

colloid-electrolyte interactions.� Intravenous fat emulsion.

�Drug Targeting and Delivery Systems


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(ii) Electrophoresis(ii) Electrophoresis

If electric potential is applied across two platinum electrodes

immersed in a hydrophilic sol the dispersed particles move toward oneimmersed in a hydrophilic sol, the dispersed particles move toward one

or the other electrode. The movement of sol particles under an applied

l i i l i ll d l h i h ielectric potential is called electrophoresis or cataphoresis.

If the sol particles here negatively charged, they migrate

toward the positive electrode. On the other hand, if they have positively

charged they move toward the negative electrode. From the direction of

movement of the sol particles, we can determine the charge of the sol

particles.


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The phenomenon of electrophoresis can be demonstrated byThe phenomenon of electrophoresis can be demonstrated by

placing a layer of As2S3 sol under two limbs of a U-tube. When a potential

diff f b 100 l i li d h l i l ddifference of about 100 volts is applied across the two platinum electrodes

dipping in deionised water, it is observed that the level of the sol drops on

the negative electrode side and rises on the positive electrode side (Fig.)

This shows that As2S3 sol has migrated to the positive electrode, indicating

that the particles are negatively charged.


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Electrophoresis is an electrokinetic process which separatesElectrophoresis is an electrokinetic process which separates

charged particles in a fluid using a field of electrical charge. It is most

f d i lif i i l l DNA doften used in life sciences to separate protein molecules or DNA and can

be achieved through several different procedures depending on the type

and size of the molecules


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(iii) Electro-osmosis(iii) Electro osmosis

In a sol, the dispersion medium carries an equal but opposite

charge to that of the dispersed particles Thus the medium will move incharge to that of the dispersed particles. Thus, the medium will move in

opposite direction to the dispersed phase under the influence of applied

l t i t ti l Th t f th di i di d thelectric potential. The movement of the dispersion medium under the

influence of applied potential is known as electro-osmosis.

The phenomenon of electro-osmosis can be demonstrated by

using a U-tube in which a plug of wet clay (a negative colloid) is fixed.

The two limbs of the tube are filled with water to the same level. The

platinum electrodes are immersed in water and potential applied acrossp p pp

them. It will be observed that water level rises on the cathode side and

falls on anode sidefalls on anode side.


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This movement of the medium towards the negative

electrode, shows that the charge on the medium is positive. Similarly,electrode, shows that the charge on the medium is positive. Similarly,

for a positively charged colloid electro-osmosis will take place in the

reverse direction.reverse direction.

Electro-osmotic flow is commonly used

in microfluidic devices, soil analysis and processing and chemicalc o u d c dev ces, so a a ys s a d p ocess g a d c e ca

analysis, all of which routinely involve systems with highly charged

surfaces, often of oxides.,


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h d lid i l d lIn electrophoresis, charged solid particles move under external

electric field. In electro-osmosis, liquid with free charge move under

external electric field where charged solid is stationary.


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topic: date liquid state-1 - 06/04/202020 only y use e · intermolecular force the intermolecular...

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