Electrochemistry (Types of Electrodes, Applications of EMF, Determination of pH)

(Faradays law of Electrolysis, Electrolysis of NaCl, Ionic Strength)

Types of Electrodes

Different Types of Electrodes

•

• • • • •

An electrochemical cell consists of two electrodes, positive

and negative. Each electrode along with the electrolyte

constitutes a half cell. The commonly used electrodes in

different electrochemical cells are

Metal-Metal ion electrodes

Metal-Amalgam electrodes

Metal insoluble metal salt electrodes

Gas electrodes

Oxidation-reduction electrodes

Metal-Metal ion electrodes

An electrode of this type consists of a metal rod (M)

dipping into a solution of its metal ions(Mn+). This is

represented as

M/Mn+

Example:

Cu rod dipping in Copper sulphate solution (Cu/Cu2+)

Metal-Metal ion electrodes

The electrode reaction may be represented as

Mn+ + ne‒ ⇌ M

If the metal rod behaves as negative electrode (i.e

the reaction involves oxidation) the equilibrium

will shift to the left and hence the concentration of

the Metal ions in the solution will increase.

On the other hand, if the metal rod behaves as

positive electrode (i.e the reaction involves

reduction), and the equilibrium will shift to the

right and hence the concentration of the metal

ions will decrease.

Metal-Amalgam Electrodes

The activities and the electrode potentials of highly

reactive metals such as sodium, potassium, etc. are

difficult to measure in aqueous solution. Hence, the

activity of the metal is lowered by dilution with

mercury.

M(Hg)/Mn+

Example

Na, Hg (C1)/Na+(C2)

Metal-Insoluble metal salt electrodes

• This type of electrode consists of a metal (M)

covered by a layer of sparingly soluble salt (MX)

dipping into a solution containing a common anion

(X‒). These electrodes are represented as

M/MX / / X‒ (a)

Example:

• (a)Calom

el

Electode: It consists o

f

Mercury-

Mercurous chloride in contact with a solution o

f

potassium chloride (Hg/Hg2Cl2, KCl)

Gas Electrodes

• In a gas electrode hydrogen gas is continuously

bubbled through a 1M solution of the acid. A inert

metal like platinum is used, since it is not attacked

by acid. The inert metal in electrode does not

participate in the electrode reaction but helps in

making electrical contact. Let the gas bubbled be X2,

then the electrode is denoted as

Pt, X2(1atm) /X+(a)

Example:

Standard hydrogen electrode: Pt, H2 (1atm)/H+(1M)

Oxidation-Reduction electrodes

(or) Red-Ox electrodes

• In this type of electrode the potential is developed

•

due to the presence of ions of the same substance

in two different valence(i.e. oxidation) states.

This electrode is set up by inserting an inert metal

like platinum in an appropriate solution containing

a mixture of ferrous (Fe2+) and Ferric (Fe3+) ions.

• In this electrode the potential is due to the

tendency of the ions to change from one oxidation

state to the other more stable oxidation state.

These electrodes are represented as

Pt/Mn +(a ), Mn + (a ) 1 1 2 2

Applications of EMF measurements

Applications of

EMF

measurements (i) Determination of valency of ion in doubtful cases

• The valency of mercurous ion can be determined by

determining the EMF of a concentration cell of the type given

below.

Hg/ Hg2(NO3)2(C1) // Hg2(NO3)2(C2) / Mercury

• The EMF of the cell, E, is given by the expression

• C1

= 0.1M) the EMF was 0.0295V. Therefore, the valency of

mercurous ion is 2, and it should be represented as .

0.059 C E = log 2

n C1

It was found that when C2/C1 was 10, (i.e. C2 = 1M and

2 2

Hg

Applications of EMF

measurements

(ii) Determination of solubility product of sparingly soluble

salt:

The solubility product constant of a sparingly soluble salt is a

kind of equilibrium constant. Consider the salt MX in

equilibrium with its ions in a saturated solution.

(s) + MX ⇌

The solubility product of the salt is given by

Ksp = [M+] [X‒]

(aq) (aq) M X

The cell is represented as M, M+

MX(s)

X‒ (sat.sol.) / / MX(s), M

X‒ R.H.E + e‒ ⇌ M

+ L.H.E M ⇌ ‒

Overall reaction MX(s) ⇌

E° =

log Ksp =

E° =

=

(aq) + e M

(aq)+ M (aq)

X

L R - E ο E ο

2.303 RT

We know that ‒ ∆G° = nFE° And ‒∆G° = 2.303 RT log Ksp

nFE

sp nF

2.303 RT log K

sp n

0.059 log K

(iii)Free energy, enthalpy and entropy changes in

electrochemical reactions:

•

The standard free energy can be calculated as follows

∆G° = ‒nFE° n= number of electrons, F = 96500 C, E° = EMF of the cell.

By knowing the standard EMF of a cell we can calculate

the entropy change using the equation

• can be calculated using the Then the

equation

enthalpy change

∆G° = ∆H° ‒ T∆S°

p

∆S° = n F T

E

Determination of pH

Determination of pH

By using a glass electrode:

It consists of thin walled glass bulb (made of

special type of glass having low melting point

and high electrical conductivity) containing a

Pt wire in 0.1M HCl. The thin walled glass bulb

functions as an ion-exchange resin, and an

equilibrium is set up between the sodium ions

of glass and hydrogen ions in solution. The

potential difference varies with the hydrogen

ion concentration, and it given by

G [E0 0.0592 pH]

Determination of pH by using a glass electrode

The cell may be represented as

Pt, 0.1M HCl/ Glass// KCl(Satd. Soln.)/ Hg2Cl2(s). Hg

The EMF of the cell is measured by

Cell E° =

Cell E° =

= 0.2422 V ‒

= 0.2422 V ‒

pH =

R L - E ο Eο

ECalomel - EGlass

G

E0

G

[E0 0.0592 pH]

0.0592 pH

0.2422 V - E0 - E G Cell

0.0592 V

Faraday’s Law of Electrolysis

Faraday’s Law of Electrolysis

First Law: According to it “during electrolysis, the

amount of any substance deposited or evolved at

any electrode is proportional to the quantity of

electricity passed” The quantity of electricity (Q) is equal to the

product of the current strength and the time for

which it is passed.

Q = current strength × time

Faraday’s Law of Electrolysis

If W is the weight of a substance

liberated/deposited at an electrode during

electrolysis, then from first law, we get:

W α Q

But Q = it

W α it W = Zit

Faraday’s Law of Electrolysis

different substance evolved/depositedby the passage of same quantity of

electricity are

Second Law: According to it “the weights of

proportional to their chemical equivalent weights

W α E

Where

W = Weight of the substance liberated or

deposited.

E = Chemical equivalent weight of the substance

liberated/deposited.

Electrolysis of aqueous sodium

chloride

When sodium chloride is dissolved in water, it

ionises as

NaCl ⇌ Na+ + Cl‒

Water also dissociates as

H+ H2O ⇌ + OH‒

When electric current is passed through

aqueous sodium chloride solution using

platinum electrodes

Electrolysis of aqueous sodium

chloride

H+ ions move towards the cathode. The H+ ions gain

electrons and change into neutral atoms. Hydrogen

atom is unstable and combines with another atom

to form stable hydrogen molecule.

Hydrogen atom is unstable and combines with

another atom to form stable hydrogen molecule

+ e‒ H (atom unstable) H+

H + H H2 (stable)

Electrolysis of aqueous sodium

chloride

Cl‒ ions move towards anode. These Cl‒ ions lose electrons

and change into neutral atoms, chlorine atom is unstable

and combines with another atom to form stable chlorine

molecule.

At Anode:

e‒ Cl‒ ‒

Cl + Cl

Cl atom (unstable)

Cl2 (stable)

Hence in the electrolysis of aqueous solution of sodium

chloride, hydrogen is liberated at cathode while chlorine is

liberated at anode.

Electrolysis of aqueous

copper sulphate

solution (using pt

electrode) When copper sulphate is dissolved in water, it ionizes as

Cu2+ CuSO4 ⇌ + SO4 2‒

H+ H2O ⇌ + OH‒ (slightly ionized)

When electric current is passed through copper sulphate

solution using platinum (Pt) electrodes:

(a) Cu2+ ions move towards cathode. These Cu2+ ions gain

electrons and change into neutral atoms and get deposited at cathode.

Cu2+ + 2e‒ Cu (deposited)

At Cathode

lose OH‒ ions move towards anode. These OH‒ ions electrons and change into neutral hydroxyl

groups.

At Anode: 2OH‒ 2OH (neutral)

The neutral hydroxyl groups being unstable react with other neutral OH‒ groups to form water and oxygen.

2OH H2O + O

O + O2

Hence during electrolysis of copper sulphate solution using

platinum electrodes, copper and oxygen are liberated.

‒ e

O

Ionic Strength

Ionic strength of solutions

Ionic strength is a measure of the

2 C Z

2

concentration of ions in that solution. Ionic

strength may be expressed as 1 i i μ

Ionic strength

Calculate the ionic strength of 0.1M solution of NaCl

2

For Na+

For Cl‒

C Z 1

2 i i μ

C = 0.1 and Z = 1

C = 0.1 and Z = 1

μ

1 (0.112 0.112 ) 0.1

2

Ionic strength

Calculate the ionic strength of 0.1M solution of

Na2SO4, MgCl2 and MgSO4 respectively.

Na2SO4

MgCl 2

MgSO4

μ 1

(0.2 12 0.1 22 ) 0.3 2

μ 1

(0.1 22 0.2 12 ) 0.3 2

μ

1 (0.1 22 0.1 22 ) 0.4

2

Ionic strength

• The ionic strength of a solution containing

more than one electrolyte is the sum of the

ionic strength of the individual salts

• comprising the solution.

Hence, the ionic strength of a solution

each at containing Na2SO 4, MgCl2 and MgSO 4

a concentration of 0.1M is 1.0.

PP.1

POLYMERS AND PLASTICS

TECHNIQUES REQUIRED : Reflux apparatus

OTHER DOCUMENTS Experimental procedure, Report template

INTRODUCTION

Chemically, plastics are chainlike molecules of high molecular weight, called polymers and are built

up from simpler chemicals, the individual links, called monomers. A different monomer or combination of

monomers is used to manufacture each different type or family of polymers. There are many polymers

around us that are so familiar we take them for granted. Examples of man-made polymers are Teflon,

nylon, Dacron, polyethylene, polyester, Orlon, epoxy, vinyl, polyurethane, silicones, Lucite, and boat resin.

Examples of natural polymers are starch and cellulose (from glucose), rubber (from isoprene) and

proteins (from amino acids). Certainly, polymers have had and continue to have a great influence on our

society. As these materials have been created, problems have arisen concerning their use. Many are not

biodegradable, they contribute a significant volume to the garbage we create and the raw materials for

their manufacture are a finite resource. Plastic recycling is an important process for reducing waste and

recovering potentially valuable raw materials, for example, it has been possible to buy fleece clothing

made from recycled materials for several years.

CHEMICAL STRUCTURES OF POLYMERS

Basically a polymer is made up of many repeating molecular units formed by sequential addition of

monomer molecules to one another. Many monomer molecules of A, say 1,000 to 1,000,000, can be

linked to form a gigantic polymeric molecule:

Many A etc etc. or

Monomer

molecules

Polymermolecule

( )A A A A A A

Monomers that are different can also be linked, to form a polymer with an alternating structure. This

type of polymer is called a copolymer.

Many A + many B etc etc. or ( )

Monomer

molecules

Polymer

molecule

A B A B A B A B

PP.2

TYPES OF POLYMERS

For convenience, chemists classify polymers in several main groups, depending on method of

synthesis.

1. Addition polymers are formed by a reaction in which monomer units simply add to one another to

form a long-chain (generally linear or branched) polymer. The monomers usually contain

carbon-carbon double bonds (whose characteristic reactions are addition reactions). Common

examples of addition polymers are polyethylene and Teflon. The process can be represented as

follows:

+ + +Branched

+ + + Linear

2. Condensation polymers are formed by reaction of bi- or polyfunctional molecules, with the

elimination of some small molecule (such as water, ammonia, or hydrogen chloride) as a

by-product. Common examples of condensation polymers are nylon, Dacron, and polyurethane.

The process can be represented as follows:

+H X H X H X + HX

3. Cross-linked polymers are formed when long chains are linked in one gigantic, 3-dimensional

structure with tremendous rigidity. Addition and condensation polymers can exist with a cross-linked

network, depending on the monomers used in the synthesis. Familiar examples of cross-linked

polymers are Bakelite, rubber, and casting (boat) resin. The process can be represented as follows:

Linear Cross-linked

Industrialists, engineers and technologists often classify polymers in other categories based on their

properties.

1. Thermoplastics are materials that can be softened (melted) by heat and re-formed (molded) into

another shape. Weaker, noncovalent bonds are broken during the heating. Technically,

thermoplastics are the materials we call plastics. Both addition and condensation polymers can be

PP.3

so classified. Familiar examples include polyethylene (addition polymer) and nylon (condensation

polymer).

2. Thermoset plastics are materials that melt initially but on further heating become permanently

hardened. They cannot be softened and remolded without destruction of the polymer because

covalent bonds are broken. Chemically, thermoset plastics are cross-linked polymers. Bakelite is

an example of a thermoset plastic.

Polymers can also be classified in other ways; for example, based on their uses, many varieties of

rubber are often referred to as elastomers, Dacron is a fiber, and polyvinyl acetate is an adhesive. The

chemical based classification will be used in this essay.

ADDITION POLYMERS

Most of the polymers made are of the addition type. The monomers generally contain a

carbon-carbon double bond. The most important example of an addition polymer is the well-known

polyethylene, for which the monomer is ethylene. Countless numbers of ethylene molecules are linked in

long-chain polymeric molecules by breaking the pi bond and creating two new single bonds between the

monomer units. The number of recurring units may be large or small, depending on the polymerisation

conditions.

Many etc. etc. or C C

H H

H H n

Ethylene

monomer

Polyethylene

polymer

C C C C

H H H H

H H H H

C C

H

H

H

H

This reaction can be promoted by heat, pressure, and a chemical catalyst. The molecules produced

in a typical reaction vary in the number of carbon atoms in their chains. In other words, a mixture of

polymers of varying length is produced, rather than a pure compound.

Polyethylenes, with linear structures, can pack together easily and are referred to as high-density

polyethylenes. They are fairly rigid materials. Low-density polyethylenes consist of branched-chain

molecules, with some cross-linking in the chains. They are more flexible than the high-density

polyethylenes. The reaction conditions and the catalysts that produce polyethylenes of low and high

density are quite different. The monomer, however, is the same in each case. Another example of an

addition polymer is polypropylene. In this case, the monomer is propylene. The polymer that results has

a branched methyl on alternate carbon atoms of the chain.

PP.4

Many etc. etc. or

n

Propylene

monomer

Polypropylene

polymer

C C C C

H H H H

H CH3

H CH3

C C

H

CH3

H

H

C C

H H

H CH3

TABLE 1. ADDITION POLYMERS

EXAMPLE MONOMER(S) POLYMER USE

Polyethylene CH2

CH2 CH

2CH

2 Most common and important polymer. Bags, insulation for wires, squeeze bottles

Polypropylene CH2

CH

CH3

CH2

CH

CH3

Fibers, indoor-outdoor carpets, bottles

Polystyrene CH2

CH

CH2

CH

Styrofoam, inexpensive household goods, inexpensive molded objects

Polyvinyl chloride (PVC)

CH2

CH

Cl

CH2

CH

Cl

Synthetic leather, clear bottles, floor covering, phonograph records, water pipe

Polytetrafluoroethylene (Teflon)

CF2

CF2 CF

2CF

2 Nonstick surfaces, chemically resistant films

Polymethyl methacrylate (Lucite, Plexiglas)

CF2

C

CO2CH

3

CH3

CH2

C

CO2CH

3

CH3

Unbreakable “glass”, latex paints

Polyacrylonitrile (Orlon, Acrilan, Creslan)

CH2

CH

CN

CH2

CH

CN

Fiber used in sweaters, blankets, carpets

Polyvinyl acetate (PVA)

CH2

CH

OCCH3

O

CH2

CH

O CCH3

O

Adhesives, latex paints, chewing gum, textile coatings

Natural rubber CH

2CCH CH

2

CH3

CH2

C CH

CH3

CH2

The polymer is cross-linked with sulfur (vulcanization)

Polychloroprene (Neoprene rubber) CH

2CCH CH

2

Cl

CH2

C CH

Cl

CH2

Cross-linked with ZnO, resistant to oil, gasoline

Styrene butadiene rubber (SBR)

CHCH2

CH2

CHCH CH2

CH2CH CH

2CH CHCH

2

_

Cross-linked with peroxides. Most common rubber. Used for tires. 25% styrene. 75% butadiene

PP.5

Several common addition polymers are shown in Table 1. Some of their principal uses are also

listed. The last three entries in the table all have a carbon-carbon double bond remaining after the

polymer is formed. These bonds activate or participate in a further reaction to form cross-linked polymers

called elastomers; this term is almost synonymous with rubber, since they designate materials with

common characteristics.

CONDENSATION POLYMERS

Condensation polymers, for which the monomers contain more than one type of functional group,

are more complex than addition polymers. In addition, most condensation polymers are copolymers made

from more than one type of monomer. You will recall that addition polymers, in contrast, are all prepared

from substituted ethylene molecules. The single functional group in each case is one or more double

bonds, and a single type of monomer is generally used.

Dacron, or polyethyleneterephthalate (PET) is a polyester, can be prepared by causing a dicarboxylic acid

to react with a bifunctional alcohol (a diol):

COOHHOOC H OCH2CH

2OH

O O

OCH2CH

2 n

O +

Terephthalic acid Ethylene glycol Dacron

H2O

PETor

Nylon 6-6, a polyamide, can be prepared industrially by causing a dicarboxylic acid to react with a

bifunctional amine:

H N(CH2)

6

H

NH

H

C(CH2)

4HO

O

C OH

O

C(CH2)

4

O

C N(CH2)

6

O

H

N

H

OH2

+

Adipic acid Hexamethylene-

diamineNylon

Notice, in each case, that a small molecule, water, is eliminated as a product of the reaction.

Several other condensation polymers are listed in Table 2. Linear (or branched) chain polymers as well as

cross-linked polymers are produced in condensation reactions.

The nylon structure contains the amide linkage at regular intervals,

N

O H

This type of linkage is extremely important in nature because of its presence in proteins and polypeptides.

Proteins are gigantic polymeric substances made up of monomer units of amino acids. They are linked by

the peptide (amide) bond.

Other important natural condensation polymers are starch and cellulose. They are polymeric

materials made up of the sugar monomer glucose. Another important natural condensation polymer is the

DNA molecule. A DNA molecule is made up of the sugar deoxyribose linked with phosphates to form the

backbone of the molecule.

PP.6

TABLE 2. CONDENSATION POLYMERS

EXAMPLE MONOMERS POLYMER USE

Polyamides

(Nylon) HOC(CH

2)n

O

COH

O

H2N(CH

2)nNH

2

C(CH2)nC NH(CH

2)nNH

O O

Fibers, molded objects

Polyesters (Dacron, Mylar, Fortrel)

HO(CH2)nOH

HOC COH

OO

C C

OO

O(CH2)nO

Linear polyesters

Fibers, recording tape

Polyesters (Glyptal resin)

C

OC

O

O

HOCH2CHCH

2OH

OH

CO

COCH2CHCH

2O

O O

Cross-linked polyester

Paints

Polyesters (Casting resin) HOCCH

O

CHCOH

O

HO(CH2)nOH

CCH

O

CHC

O

O(CH2)nO

Cross-linked with styrene and peroxide. Fiberglass boat resin

Phenol-formaldehyde resin (Bakelite)

OH

CH2

O

CH2

OH

CH2

CH2

OH

CH2

CH2

Mixed with fillers. Molded electrical goods, adhesives, laminates, varnishes

Cellulose acetate*

O

O

CH2OH

O

OH

OH

CH3COOH

O

O

CH2OAc

O

OAc

OAc

Photographic film

Silicones

Cl Si Cl

CH3

CH3

H2O

O Si O

CH3

CH3

Water-repellent coatings, temperature-resistant fluids and rubbers (CH3SiCl3 cross-links in

water)

Polyurethanes CH3

N

N C O

C O

HO(CH2)nOH

CH3

NH

NH

C

O

O(CH2)nO

C

O

O(CH2)nO

Rigid and flexible foams, fibers

* Cellulose, a polymer of glucose, is used as the monomer.

PP.7

PROBLEMS WITH PLASTICS

Plastics have certainly become very common in our society. However, they are not without

problems. There are disposal problems, health hazards, littering problems, fire hazards, and energy

shortages associated with their manufacture and use.

Plasticizers and Health Hazards

Certain types of plastics such as polyvinyl chloride (PVC) are mixed with plasticizers that soften the

plastic so that it is more pliable. If plasticizers were not added, the plastic would be hard and brittle.

Some of the plasticizers used in vinyl plastics are phthalate esters. The structure of a phthalate ester is

shown over. These esters are volatile compounds of low molecular weight. Part of the new car "smell"

comes from the odor of these esters as they evaporate from the vinyl upholstery. The vapor often

condenses on the windshield as an oily, insoluble film. After some time, the vinyl material may lose

enough plasticizer to cause it to crack. Phthalate esters may constitute a health hazard. Sometimes vinyl

containers incorporating phthalate plasticizers are used to store blood. The esters are leached from blood

bags made of PVC and may be partly responsible for shock lung, a condition that sometimes leads to

death during a blood transfusion. The long-term effects of these plasticizers are, however, not known.

Recently, a rare and fatal form of liver cancer (angiosarcoma) was discovered among small

numbers of workers in chemical companies making polyvinyl chloride. The monomer used in making

PVC is vinyl chloride, a gas. The structure is shown in Table 1. Currently, industry is required to eliminate

this health hazard by reducing or eliminating vinyl chloride from the atmosphere.

Other types of plasticizers once used were the polychlorinated biphenyls (PCB). These compounds

and DDT have similar physiological effects, and they are even more persistent in the environment! The

PCBs are actually a mixture of compounds that have had the hydrogens on the basic hydrocarbon

structure, biphenyl, replaced with chlorines (from one to ten hydrogens can be replaced). One typical PCB

that may be present in a plasticizer mixture is shown. PCBs are no longer being sold except for use in

closed systems, where they cannot leak into the environment.

COCH2CH

2CH

2CH

3

COCH2CH

2CH

2CH

3

O

OCl

Cl

Cl Cl

CH2

CHCl

Dibutyl phthalate Vinyl chloride A polychlorinated biphenyl (PCB)

Disposal Problems

What do we do with all our waste? One of the most popular methods is to bury our garbage in

landfills. However, as we run out of good places to bury our garbage, incineration appears to be an

attractive method for solving the solid waste problem. It is currently estimated that about 64,000,000,000

kg of plastics are discarded per year in the United States : that's over 270 kg per person. About 80% of

this plastic currently ends up in landfill sites, and so plastics account for about 25% of the volume of

landfill refuse.

PP.8

One possible option to reduce landfill waste is to combust the plastics that burn readily. The new

high-temperature incinerators are extremely efficient and can be operated with very little air pollution. It

should also be possible to burn our garbage and generate electrical power from it, albeit with the

production of carbon dioxide, a critical greenhouse gas.

Ideally, we should either recycle all our wastes or not produce the waste in the first place. Plastic waste

consists of about 55% polyethylene and polypropylene, 20% polystyrene, and 11% PVC. All these

polymers are thermoplastics and can be recycled. They can be resoftened and remolded into new goods.

Unfortunately, thermosetting plastics (cross-linked polymers) cannot be remelted. They decompose on

high-temperature heating. Thus, thermosetting plastics should not be used for "disposable" purposes.

Alternative techniques to simple reforming are depolymerisation. This allows us to recover the monomers

for purification and potential repolymerisation. The depolymerisation of PET (a polyester found in soft

drink bottles) will be carried out as part of this experiment. Polyester clothing can be recycled and reused

in new polyester product and polyester clothing can be made from recycled PET. In order to recycle

plastics effectively, we must sort the materials according to the various types. This requires will power as

well as knowledge about the plastics that we are discarding. Neither requirement is easily effected.

Littering Problems

Plastics, if they are well made, will not corrode or rust, and they last almost indefinitely.

Unfortunately, these desirable properties also lead to a problem when plastics are buried in a landfill or

thrown on the landscape - they do not decompose. Currently, research is being undertaken to discover

plastics that are biodegradable or photodegradable, so that either microorganisms or light from the sun

can decompose our litter and garbage. Some success has been achieved.

Fire Hazards

Numerous injuries are caused by clothing made of polymers, especially children's clothing. Many of

these organic fibers burn readily. To combat this problem, chemists have developed flame-retardant

fabrics, especially for children's sleepwear.

Toxic gases are sometimes liberated when plastics burn. For example, hydrogen chloride is

generated when PVC is burned, and hydrogen cyanide when polyacrylonitriles are burned. This presents

a problem that compounds the fire danger.

Energy Shortage

The demand for energy has increased at an alarming rate, leading to the energy crisis. The

production of polymers requires petroleum as a raw material and as a source of energy to conduct

manufacturing. Unfortunately, fossil fuels are a nonrenewable resource, and as their availability

decreases, we shall have an even greater problem. On the other hand, natural substances, such as

cotton are renewable resources; perhaps for some uses they would actually be better and less costly than

the synthesized polymers. There are many plastics, however, that are superior to natural materials. The

answer lies in using and reusing plastics wisely.

PP.9

EXPERIMENT

There are two parts to this experiment. In the first part, a polyester will be "recycled" from a soft

drink bottle by depolymerisation via base promoted saponification and one of the raw materials recovered.

The second part is a demonstration of the synthesis of the polyamide nylon. These polymers represent

some of the most important commercial plastics.

A. POLYESTERS

Polyesters are examples of condensation polymers. Polyethyleneterephthalate (PET), a linear

polyester, will be depolymerised and the terephthalic acid recovered by the hydrolysis of the ester linkages

in the polyester using potassium hydroxide in refluxing pentanol:

COOHHOOC H OCH2CH

2OH

Terephthalic acid Ethylene glycol

O O

OCH2CH

2 n

-OCH

2CH

2O O

O

Portion of a linear polyester

(a diol)

KOH / heat

1-pentanol

then add HCl

In principle it is possible to use the product to make other polymers or other chemicals. A linear polyester

will be prepared as follows:

+

Phthalic

anhydride

Ethylene glycol

(A diol)

+

+

CCCH2CH

2O OCH

2CH

2

O O

O O

H2O

CCHO OCH2CH

2OH

O O

CCHO OCH2CH

2OH

O O

HO CH2CH

2OH

Linear polyester

HOCH2CH

2OH

C

O

CO O

This linear polyester is isomeric with Dacron (which is prepared from terephthalic acid and ethylene

glycol). Dacron and the linear polyester made in this experiment are both thermoplastics.

If more than two functional groups are present in one of the monomers, then the polymer chains

can be linked to one another (cross-linked) to form a three-dimensional network. Such structures are

usually more rigid than linear structures and are useful in making paints and coatings and are

classified as thermosetting plastics. The polyester Glyptal is prepared as follows:

10

O

O

O

+

HO OCH2CHCH

2OH

O O OH

Phthalic

anhydride

Glycerol

(A triol)

O O

OCH2CHCH

2O

O

OCH2CHCH

2O

O

+

HOCH2CHCH

2OH

OH

HOCH2CHCH

2OH

OH

Cross-linked polyester

(Glyptal resin)

H2O

The reaction of phthalic anhydride with a diol (ethylene glycol) is described in the procedure.

This linear polyester is compared with the cross-linked polyester (Glyptal) prepared from phthalic

anhydride and a triol (glycerol).

B. POLYAMIDE (NYLON)

Reaction of a dicarboxylic acid, or one of its derivatives, with a diamine leads to a linear

polyamide through a condensation reaction. Nylon and Kevlar, familiar for its strength and application

in bullet-proof vests etc. are polyamides. Commercially, nylon 6-6 (so called because each of the

monomer units has 6 carbons) is made from adipic acid (1,6-hexadioic acid) and

hexamethylenediamine (1,6-diaminohexane) In this experiment, you use the more reactive acid

chloride instead of adipic acid:

+

Adipoyl chloride

Cl CCH2CH

2CH

2CH

2C Cl

O O

CCH2CH

2CH

2CH

2C NCH

2CH

2CH

2CH

2CH

2CH

2N

O HO H

Nylon 6-6

Hexamethylenediamine

H NCH2CH

2CH

2CH

2CH

2CH

2N H

H H

The acid chloride is dissolved in cyclohexane and this is added carefully to hexamethylenediamine

dissolved in water. These liquids do not mix, and two layers will form. At the point of contact between

the layers (interface), the nylon forms. It can then be drawn out continuously to form a long strand of

nylon. Imagine how many molecules have been linked in this long strand! It is a fantastic number.

GENERAL PRINCIPLE OF EXTRACTION OF METALS

Metals and non metals:

Elements vary in abundance. Metals are opaque, lustrous elements that are good conductors of

heat and electricity. Most metals are malleable and ductile and are, in general, denser than the

other elemental substances. Non-metal is a chemical element that does not have the properties of

a metal. Seventeen elements are generally classified as nonmetals; most are gases (hydrogen,

helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one is a

liquid (bromine), and a few are solids (carbon, phosphorus, sulfur, selenium, and iodine).

Among metals, aluminium is the most abundant. It is the third most abundant element in earth’s

crust (8.3% approx. by weight). It is a major component of many igneous minerals including

mica and clays. Many gemstones are impure forms of Al2O3 and the impurities range from Cr

(in ‘ruby’) to Co (in ‘sapphire’). Iron is the second most abundant metal in the earth’s crust. It

forms a variety of compounds and their various uses make it a very important element. It is one

of the essential elements in biological systems as well.

Comparison of physical and chemical properties of metals and non metals:-

S.No Property Metals Non-Metals

1 Physical State Metals are solid at

room temperature.

Except mercury and

gallium.

Non-metals

generally

exist as solids and

gases, except

Bromine.

2 Melting and boiling points Metals generally

have high m.pt and

b.pt except gallium

and cesium.

Non-metals have

low m.pt and b.pt

except diamond

and graphite.

3 Density Generally high. Generally low.

4 Malleability and Ductility Malleable and

ductile.

Neither malleable

nor

ductile.

5 Electrical and thermal

conductivity

Good conductors of

heat and electricity.

Generally poor

conductors of heat

and electricity

except graphite.

6 Luster Poses shining luster. Do not have luster

except iodine.

7 Sonorous sound Give sonorous

sound

when struck.

Does not give

sonorous sound.

8 Hardness Generally hard

except

Na, K

Solid non-metals

are

generally soft

except diamond.

Comparison of Chemical Properties of Metals and Non-metals:-

1 Reaction

with

Oxygen

Metals form basic oxides

Zn and Al form

amphoteric oxides (they

show the properties of

both acidic and basic

oxides)

Most of the metal oxides

are insoluble in water

Some of them dissolve to

form Alkali.

Non-metals form acidic

oxides

CO and HO2O are neutral

oxides(they are neither

acidic nor basic in nature)

Non- metal oxides are

soluble in water

They dissolve in water to

form acids.

2 Reaction

with

water

Metals react with water to

form metal oxides or

metal hydroxide and H2

gas is released.

Non-metals do not react

with water, steam to evolve

hydrogen gas. Because non-

metals cannot give electrons

to hydrogen in water so that

it can be released as H2 gas.

3 Reaction

with salt

solutions

When metals react with

salt solution, more

reactive metal will

displace a less reactive

metal from its salt

solution.

When non-metals react

with salt solution, more

reactive non-metal will

displace a less reactive non-

metal from its salt solution.

4 Reaction

with

Chlorine

Metal Chloride forms and

ionic bond is formed.

Therefore Ionic

compound is obtained.

Non-metal Chloride forms

and covalent bond is

formed. Therefore covalent

compound is obtained.

5 Reaction

with

Hydrogen

Metals react with

hydrogen

to form metal hydride

This reaction takes place

only for most reactive

metals.

Non-metals react with

hydrogen to form hydrides

Minerals:

A mineral is a naturally occurring substance having a definite chemical composition, constant

physical properties, and a characteristic crystalline form. Ores are a mixture of minerals: they are

processed to yield an industrial mineral or treated chemically to yield a single or several metals.

Ores that are generally processed for only a single metal are those of iron, aluminium, chromium,

tin, mercury, manganese, tungsten, and some ores of copper. Gold ores may yield only gold, but

silver is a common associate. Nickel ores are always associated with cobalt, while lead and zinc

always occur together in ores. All other ores are complex yielding a number of metals. Ores

undergo a beneficiation process by physical methods before being treated by chemical methods

to recover the metals. Beneficiation processes involve liberation of minerals by crushing and

grinding then separation of the individual mineral by physical methods (gravity, magnetic, etc.)

or physicochemical methods (flotation). Chemical methods involve hydrometallurgical,

pyrometallurgical, and electrochemical methods.

Types of ores:

Oxide ores: Examples: Fe2O3, Fe3O4 Apart from Fe, other heavy metals which are

produced from oxide ores are: Manganese, Chromium, Titanium, Tungston, uranium and

Tin.

Sulphide ores: Copper ore (CuFeS2, Chalcopyrite), sphalerite (Zn,Fe)S, Galena PbS,

Pyrite FeS2. Others: Nickel, Zinc,Mercury and Molybdenum.

Halide ores: Rock salts of Sodium, Magnesium chloride in sea water.

List of Important metals and their ores list

S.No Metal Ores

1. Aluminium(Al) Bauxite, Corundum, Feldspar, Cryolite, Alunite, Kaolin.

2. Magnesium(Mg) Magnesite, Dolomite, Epsom salt, Kieserite, Carnalite

3. Calcium(Ca) Dolomite, Calcite, Gypsum, Fluorspar, Asbestos.

4. Copper(Cu) Cuprite, Copper glance, Copper pyrites.

5. Iron(Fe) Haemethite, Limonite, Magnetite, Siderite, Iron pyrite, Copper pyrites.

METALLURGY:

Metallurgy is the science and technology of extracting metals from their ores, refining them and

preparing them for end use. Metallurgy examines the microstructure of a metal, the structural

features that are subject to observation under a microscope. Microstructure determines the

mechanical properties of a metal, including its elastic and plastic behavior when force is applied.

Chemical composition is the relative content of a particular element within an alloy, and is

usually expressed in weight percent. Composition, as well as mechanical and thermal processing

determine microstructure.

Classification based upon methods of metal extraction

Physical seperation/Mineral processing: The objective is to concentrate the metallic content in

the ore, achieved by a series of comminition (crushing and grinding), screening and seperation

process

Pyrometallurgy: It involves the smelting, converting and refining of metal concentrate.

Hydrometallurgy: It involoves the precipitation of metal in an aqueous solution.

Electrometallurgy: Electrolysis process to extract metal. Electrowinning: Extraction of the

metal from electrolyte; Electrorefining: Refining of impure metals in the form of an anode.

Classification on the basis of types of work performed:-

These divisions are extractive metallurgy, sometimes called chemical metallurgy, and physical

metallurgy.

Physical metallurgy deals with the refined metals. This branch has a wide scope that ranges

from a study of what the metals are and why they behave as they do, to production of a new or

improved product through alloying or heat treating, and is concerned with the working and

shaping of metals, by processes that change shape and size. Included in the broadest sense are

machining, rolling, bending, and wire drawing, as well as casting and powder metallurgy.

Extractive metallurgy deals with the liberation of metals by various chemical processes from

the ores in which they are found. The extractive metallurgist is also charged with refining the

metals to a purity that can be used in industry.

GENERAL STEPS OF METALLURGY:

(1) Crushing and Pulverization of Ores

The ore is generally obtained as big rock pieces. These big lumps of the ore are crushed to

smaller pieces by using jaw-crushers and grinders.

The big lumps of the ore are brought in between the plates of a crusher forming a jaw. One of the

plates of the crusher is stationary while the other moves to and fro and the crushed pieces are

collected below.

The crushed pieces of the ore are then pulverized (powdered) in a stamp mill. The heavy stamp

rises and falls on a hard die to powder the ore. The powdered ore is then taken out through a

screen by a stream of water.

Pulverization can also be carried out in a ball mill. The crushed ore is taken in a steel cylinder

containing iron balls. The cylinder is set into revolving motion. The striking balls pulverize the

crushed ore into fine powder.

(2) Concentration of Ores:

Removal of the unwanted materials (e.g., sand, clays, etc.) from the ore is known as

concentration, dressing or benefaction. It involves several steps and selection of these steps

depends upon the differences in physical properties of the compound of the metal present and

that of the gangue. The type of the metal, the available facilities and the environmental factors

are also taken into consideration. Some of the important procedures are described below.

Hydraulic Washing: This is based on the differences in gravities of the ore and the

gangue particles. It is therefore a type of gravity separation. In one such process, an

upward stream of running water is used to wash the powdered ore. The lighter gangue

particles are washed away and the heavier ores are left behind.

Magnetic Separation: This is based on differences in magnetic properties of the ore

components. If either the ore or the gangue (one of these two) is capable of being

attracted by a magnetic field, then such separations are carried out (e.g., in case of iron

ores). The ground ore is carried on a conveyer belt which passes over a magnetic roller.

Froth Floatation Method: This method has been in use for removing gangue from

sulphide ores. In this process, a suspension of the powdered ore is made with water. To it,

collectors and froth stabilisers are added. Collectors (e. g., pine oils, fatty acids,

xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilisers (e.

g., cresols, aniline) stabilise the froth. The mineral particles become wet by oils while the

gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a

result, froth is formed which carries the mineral particles. The froth is light and is

skimmed off. It is then dried for recovery of the ore particles. Sometimes, it is possible to

separate two sulphide ores by adjusting proportion of oil to water or by using

‘depressants’. For example, in case of an ore containing ZnS and PbS, the depressant

used is NaCN. It selectively prevents ZnS from coming to the froth but allows PbS to

come with the froth.

(3) Extraction extraction of crude of crude metal from concentrated

concentrated ore:

The concentrated ore must be converted into a form which is suitable for reduction.

Usually the sulphide ore is converted to oxide before reduction. Oxides are easier to

reduce (for the reason see box). Thus isolation of metals from concentrated ore involves

two major steps viz., (a) conversion to oxide, and (b) reduction of the oxide to metal.

(a) Oxidation of ore:

(b) Reduction of oxide to the metal:

Reduction of the metal oxide usually involves heating it with some other substance

acting as a reducing agent (C or CO or even another metal). The reducing agent (e.g.,

carbon) combines with the oxygen of the metal oxide.

MxOy + yC → xM + yCO

Metals which are low in the activity series (like Cu, Hg, Au) are obtained by heating

their compounds lD air: metals which are in the middle of the activity “cries (like Fe.

Zn, Ni, Sn) are obtained by heating their oxides with carbon while metals which are

very high in the activity series (e.g., Na, K, Ca, Mg, Al) are obtained by electrolvtic

reduction method.

(i) Smelting (reduction with carbon): The process of extracting the metal by

fusion of its oxide ore with carbon (C) or CO is called smelting. It is carried

out in a reverberatory furnace. During smelting a substance. called flux is

added which removes the non-fusible impurities as fusible slag. This slag is

insoluble in the molten metal and is lighter than the molten metal. So, it floats

over the molten metal and is skimmed off. Acidic flux For basic impurities,

acidic flux is added. e.g., CaO + SiO2 → CaSiO3

In the extraction of Cu and Fe, the slag obtained are respectively FeSiO3 and

CaSiO3. The obtained slag is used in road making as well as in the

manufacturing of cement and fertilizers.

(ii) Electrolytic reduction or electrometallurgy: It is the process of extracting

highly electropositive (active) metals such as Na, K, Ca, Mg, Al, etc by

electrolysis of their oxides, hydroxides or chlorides in fused state, e.g., Mg is

prepared by the electrolysis of fused salt of MgCl2 (Dow’s process).

(4) Refining or Purification of Crude Metals

Physical Methods

(i) Liquation: This method is used for refining the metals having low melting points

(such as Sn. Pb, Hg, Bi) than the impurities, The impure metal is placed on the

sloping hearth and is gently heated. The metal melts and flows down leaving

behind the non-fusible impurrties.

(ii) Distillation: This is useful for low boiling metals such as Zn, Hg. The impure

liquid metal is evaporated to obtain the pure metal as distillate.

(iii) Cupellation: This method is used when impure metal contains impurities of other

metals which form volatile oxides. e.g., traces of lead ore removed from silver (as

volatile PbO) by this process.

Chemical Methods

(i) Poling: This method is used when the impure metal contains impurities of Its own

oxide, e.g., CU2O in blister copper and SnO2 in impure Sn. The molten impure

metal is stirred with green wood poles. At this high temperature, wood liberates

gases such as CH4 which reduces any oxides present in the metal.

(ii) Electro-refining: In this method, impure metal forms the anode while the cathode

is a rod or sheet of pure metal. The electrolytic solution consists of a soluble salt

of the metal.

ALLOY:

An alloy is a mixture of 2 or more metals which display metallic bonding. The physical

properties in alloys (and in some cases, chemical properties) change in comparison to the

original metals. They are useful because they do not oxidize easily, and do not interfere with a

reaction since they cannot act as a catalyst. They are also usually more stable and harder than the

original metals due to the difference in atomic radius of the bonded metals.

Properties of an Alloy

An alloy is a metallic intimately mixed solid mixture of two or more different elements, at least

one of which is metal. In molten state alloys are homogeneous and in solid state they may be

homogeneous or heterogeneous. Metal Alloys have both physical and chemical properties

together with mechanical. Some properties are reactivity, electrical conductivity, thermal

conductivity, good tensile strength, resistance to deformation, malleability etc.

List of Important Alloys and their Uses

Alloys Compositions Uses

Brass Cu + Zn In making utensils.

Bronze Cu + Sn In making coins, bell and utensils.

German Silver Cu + Zn + Ni In making utensils.

Rolled Gold Cu + Al In making cheap ornaments.

Gun Metal Cu + Sn + Zn + Pb In making guns, barrels, gears and

bearings.

Dutch metal Cu + Zn In making artificial ornaments.

Delta metal Cu + Zn + Fe In making blades of aeroplane.

Munz metal Cu + Zn In making coins.

Monel metal Cu + Ni For base containing container.

Rose metal Bi + Pb + Sn For making automatic fuse.

Duralumin Al + Cu + Mg + Mn For making utensils.

Magnalium Al + Mg For frame of aeroplane.

Solder Pb + Sn For soldering.

Type metal Sn + Pb + Sb In printing industry.

Bell metal Cu + Sn For casting bells and statues.

Stainless steel Fe + Cr + Ni + C For making utensils and surgical

cutlery.

Nickel steel Fe + Ni For making electrical wire, automobile

parts.

Aluminum Alloys: Aluminum is not a very strong metal, but its conductive qualities

make it useful for a variety of applications. For this reason, manufacturers mix aluminum

with other metals to strengthen it, forming several different aluminum alloys. Alloys

using aluminum include alnico, which contains nickel, iron and cobalt; magnalium,

which contains magnesium and duraluminium, also known as duralumin and duralium,

which contains copper and, in some instances, magnesium and manganese. While

manufacturers use alnico in the production of magnets, they use magnalium primarily in

instruments. Duraluminium is often a component in car and aircraft engines.

Iron Alloys: The most well-known alloy of iron is steel, which can contain from 0.5

percent to 1.5 percent of carbon as its supplemental element. The carbon helps prevent

the iron from rusting, and makes it stronger. People use the material widely in

construction, such as for making screws, nails and beams for buildings and bridges. A

variation on the alloy is stainless steel, which also contains nickel and chromium in

addition to carbon. These elements help keep the metal shiny and intensify its resistance

to corrosion. Manufacturers use stainless steel in a variety of different applications, such

as for building tools, eating utensils, furniture and appliances such as refrigerators and

ranges.

Copper Alloys: The element copper is prone to oxidation, which makes it surface turn a

dull, pale-greenish color. To prevent oxidation, and to increase its strength,

manufacturers fuse copper with several different elements. One of the most common

copper alloys is brass, which contains approximately 20 percent zinc. Manufactures often

use the alloy for decorative items such as jewelry, as well as for nuts and bolts. Another

common copper alloy is bronze, which contains about 10 percent tin. Nowadays, people

commonly use bronze for making coins, statues and, as with copper, decorative items.

Gold Alloys: As a soft metal, pure gold is easy to work. For this reason, jewelry makers

often mix it with other elements to increase its strength. The most common gold alloys

include yellow gold, which contains copper, silver -- and in some instances cobalt -- and

white gold, which contains copper, zinc, nickel and, in some instances, palladium. All

types of jewelry, such as rings, bracelets, necklaces and earrings consist of both these

alloys.

Purpose of Making Alloys

Pure metals possess few important physical and metallic properties, such as melting point,

boiling point, density, specific gravity, high malleability, ductility, and heat and electrical

conductivity. These properties can be modified and enhanced by alloying it with some other

metal or nonmetal, according to the need.

Alloys are made to:

Enhance the hardness of a metal: An alloy is harder than its components. Pure metals are

generally soft. The hardness of a metal can be enhanced by alloying it with another metal or

nonmetal.

Lower the melting point: Pure metals have a high melting point. The melting point lowers

when pure metals are alloyed with other metals or nonmetals. This makes the metals easily

fusible. This property is utilized to make useful alloys called solders.

Enhance tensile strength: Alloy formation increases the tensile strength of the parent metal.

Enhance corrosion resistance: Alloys are more resistant to corrosion than pure metals. Metals

in pure form are chemically reactive and can be easily corroded by the surrounding

atmospheric gases and moisture. Alloying a metal increases the inertness of the metal, which,

in turn, increases corrosion resistance.

Modify color: The color of pure metal can be modified by alloying it with other metals or

nonmetals containing suitable color pigments.

Provide better castability: One of the most essential requirements of getting good castings is

the expansion of the metal on solidification. Pure molten metals undergo contraction on

solidification. Metals need to be alloyed to obtain good castings because alloys expand.

•

1.

2.

3.

4.

Fluid which is introduced in between moving parts in order to reduce the friction, generated heat & wear and tear of machine parts are called Lubricants.

This process of introducing lubricant is called Lubrication.

Functions of lubricants :

a) Reduces the frictional resistance. b) Reduces wear & tear, surface

deformation

c) Acts as a coolant

d) Provides protection against corrosion

e) Acts as a seal in some cases

f) ) Improves the efficiency of the machine

A good lubricating oil should

have:

• High boiling point • Adequate Viscosity • Low freezing point • High oxidation resist • Non Corrosive properties • Good thermal stability

Types Of Lubrications

Thick Film

or

Fluid Film

or

hydrodynamic Lubrication

Thin Film

or

Boundary

Lubrication

Extreme Pressure

Lubrication

• This is also called Hydrodynamic or fluid film lubrication.

• Two sliding metal surfaces are separated from each other by a thick

o

•

• •

film of fluid ( 1000 A thick).

The coefficient of friction in such cases is as low as 0.001 to 0.03

Lubricants used : Hydrocarbon Oils.

Provided in delicate instruments such as watches, clocks, light machines like sewing machines, scientific instruments etc.

•

• •

• •

•

This lubrication is also called Boundary Lubrication.

Its used for high load conditions.

Very thin film of the lubricant is adsorbed on the surface by physical or chemical forces or both.

The coefficient of friction is 0.05 to 0.15

Lubricants used for boundary lubrication should have high viscosity index, resistance to heat and oxidation, good oiliness.

Examples are Organic oils, Vegetable oils, Graphite and MoS2, Mineral Oils etc.

•

•

•

•

•

•

This lubrication is for very high press/temp/speed sliding surfaces.

Extreme pressure additives are used along with the lubricants.

Chemicals used are compounds of Cl, S & P.

These additives form solid surface films of Cl, S & P.

High melting point metal compounds are good lubricants.

E.g. graphite is used for drawing wires made up of mild steel.

Classification of Lubricants

Liquid Lubricants

Eg.Mineral Oil, Petroleum Oil, Vegetable Oil etc

Semi Solid Lubricants

Eg. Petroleum jellies

Solid Lubricants

Eg. Graphite, Molybdenum Disulphide etc.

• •

• • •

•

• • •

It’s a measure of a fluid’s resistance to flow.

Viscosity of the lubricating oil determines its performance under operating conditions.

A low viscosity oil is thin and flows easily .

A high viscosity oil is thick and flows slowly.

As oil heats up it becomes more viscous (Becomes thin)

Too low viscosity of the liquid > Lubricant film cannot be maintained between the moving surfaces > Excessive wear.

Too high viscosity of the liquid > Excessive friction.

Selected Lubricant must be proper viscous.

Viscosity is usually expressed in centipoise or centistoke.

Viscosity Index :

•

• •

•

It is “Avg. decrease in viscosity of oil per degree rise in temp between 1000F & 2100F.” Viscosity of liquids decreases with increasing temperature.

The rate at which viscosity of a lubricant changes with temperature is measured by a scale called Viscosity Index.

Silicones, polyglycol ethers, Diesters or triesters have high Viscosity Index.

Determination of Viscosity Index :

• First the viscosity of the oil under test is determined at 100°F & 210°F. Let it be U and V respectively.

Then viscosity of Pennsylvanian oil is determined. Let it be VH. • • Then viscosity of Gulf oil is determined. Let it be VL

viscosity Index = VL- U x 100

VL- VH

V.I. = 100 (Pennsylvanian oils.)

V.I. = Zero (Naphthanic-base gulf oils)

Higher the V.I, lesser is the variation of viscosity with change in temperature.Thus, a good lubricating oil should possess high V.I.

Viscosity

Temp 200

L

U

H

100OF

•

• • •

Iodine number is the number of Gms equivalent of iodine to amount of ICl absorbed by 100gm of oil. Each oil has its specific Iodine Number. So Iodine Number determines the extent of contamination of oil. Low Iodine Number is desirable in oils.

Some oils and their Iodine Numbers are given below :

Iodine Number Oil Example

>150 Drying oil Linseed oil, tung oil

100-150 Semidrying oil Castor oil , Soyabean oil

<100 Non-Drying oil Coconut oil, Olive oil

•

• •

• •

Aniline point is the Min temp at which oil is miscible with equal amt of aniline Aniline Point is a measure of aromatic content of the lubricating oil. Low Aniline Point oil have high aromatic content which attacks rubber seals. Higher Aniline point means low %age of hydrocarbons (desirable). Thus Aniline Point is used as an indication of possible deterioration of rubber sealing etc.

Determination of Aniline Point :

Aniline + sample oil

(equal)

Heated in Test tube

Homogeneous solution

Co

ole

d

Cloudiness

The temperature at which separation of the two phases (Aniline + oil) takes place is the Aniline Point.

• • •

•

• •

•

Emulsification is the property of water to get mixed with water easily. Emulsions can be oil in water emulsion or water in oil emulsion. A good lubricating oil should form such an emulsion with water which breaks easily. This property is called demulsification. The time in seconds in which a given volume of oil and water separates out in distinct layers is called steam demulsification number. A good lubricating oil should have lower demulsification number. Quicker the oil separates out from the emulsion formed, better is the lubricating oil. In cutting oils the higher the emulsification number, better the oil is. This is because the emulsion acts as a coolant as well as a lubricant.

•

•

• • •

Flash Point is the min temp at which the lubricant vaporizes that ignite for a momwhen tiny flame is brought near.

Fire Point is the Min temp at which the lubricant’s vapours burn constantly for 5 seconds when tiny flame is brought near.

Fire point = flashpoint+5 to 400C.

Both should be higher than the max temp of country (for transportation)

If flash point < 140°F = Flammable liquids

And if flash point > 140°F =Combustible liquids.

The flash and fire points are generally determined by using Pensky-Marten’s apparatus.

•Oil under examination is filled in the oil cup up to the mark and heated by the air bath by a burner. •Stirrer is worked b/n tests at a rate of about 1 – 2 rev/sec. •Heat is applied so as to raise the oil temp by about 5c/min. •The temp at which distinct flash appeared in side the oil cup is recorded as flashpoint. •The heating is continued to record the fire point.

• Drop Point is the Temperature at which grease passes from the semi- solid to the liquid state. So, it determines the upper temp limit for the applicability of grease.

Determination : • • •

•

Beaker is heated. Temperature is raised. Grease sample passes from a semi- solid to a fluid state. Temp at which its first drop falls from the opening is recorded as drop-point.

•

• • •

•

•

•

Cloud Point is the temp at which the lubricant becomes cloudy or hazy when cooled.

Pour Point is the temp at which the lubricant just ceases to flow when cooled.

Both indicates suitability of lubricant in cold conditions and thus must be low.

Pour point of wax can be lowered by dewaxing or adding suitable pour point depressant.

Pour point of an oil can be lowered by lowering the viscosity of the oil which is achieved by removing the viscous constituent of the oil.

Lubricating oils used in capillary feed systems should have low cloud points, otherwise impurities will clog the capillary.

A high pour point leads to the solidification of the lubricant that may cause jamming of the machine.

• •

•

•

Neutralization Point determines Acidity or Alkalinity of oil. Acidity/Acid value/Acid number is mgs of KOH required to neutralize acid in 1 gm of oil. Alkalinity/Base value/Base number is mgs of acid required to neutralize all bases in 1 gm oil. As Neutralization Point of oil increases, age of oil decreases.

• •

• •

It’s the mgs of KOH required to saponify 1 gm of oil. Saponification is hydrolysis of an Easter with KOH to give alcohol and Na/K salt of acid. Mineral oils do not react with KOH and are not saponifiable. Vegetable and animal oils have very high saponification values.

Significance

•

•

Saponification value helps us to ascertain whether the oil under reference is mineral or vegetable oil or a compounded oil. Each oil has its specific Soaponification Number. Deviation from it indicates the extent of adulteration of oil.

•http://www.youtube.com/watch?v=IOepo1Vlshc&feature=related •http://www.youtube.com/watch?v=uBZqWLnP0mI&feature=relmfu •http://www.youtube.com/watch?v=u5RA3zHLIdM •http://www.youtube.com/watch?v=41D0qmMfkGE&feature=relmfu •http://www.youtube.com/watch?v=1ZLrHrWwQEI

WATER

Water is nature's most wonderful, abundant and useful compound. Of the many essential

elements for the existence of human beings, animals and plants (wiz. air, water, food,

shelter, etc.), water is rated to be of the greatest importance. Without food, human call

survives for a number of days, but water is such an essential thing that without it one

cannot survive.

Water is not only essential for the lives of animals and plants, but also occupies a unique

position in industries. Probably, its most important use as an engineering material is in

the 'steam generation '. Water is also used a coolant in power and chemical plants. In

addition to it, water is widely used in other fields such as production of steel, rayon,

paper, atomic energy, textiles, chemicals, ice, and for air-conditioning, drinking, bathing,

sanitary, washing, irrigation, fire-fighting, etc.

Occurrence: Water is widely distributed in nature. It has been estimated that about 75%

matter on earth’s surface consists of water. The body of human being consists of about

60% of water. Plants, fruits and vegetables contain 90-95% of water.

Sources of Water:

Different sources of water are:

1. Surface Waters: Rain water (purest form of natural water), River water, Lake Water,

Sea water (most impure form of natural water).

2. Underground Waters: Spring and Well water. Underground waters have high organic

impurity.

TYPES OF WATER BASED ON HARDNESS

• Hard Water

• Soft Water

SOFT WATER:

Soft water is surface water that contains low concentrations of ions and in particular is

low in ions of calcium and magnesium. Soft water naturally occurs where rainfall and the

drainage basin of rivers are formed of hard, impervious and calcium-poor rocks.

Advantages of soft water:

– keeps water using/heating appliances clean and deposit free

– Since soft water lathers easily with soap, it helps in saving a lot of soap when used

in washing. It is therefore economical to use soft water in washing.

– Unlike the hard water, soft water does not form scales in kettles or pipes when it

stays long in these containers.

Disadvantages of soft water:

– It often adds salt to environment

– Can have slimy/soapy feeling even when completely rinsed

– Not as good for you to drink (less minerals)

– Calcium and magnesium ions are required for normal metabolism in many

organisms including mammals. The lack of these ions in soft water has given rise

to concerns about the possible health impacts of drinking soft water,

including sudden cardiac death.

HARDNESS OF WATER:

Hardness in water is that characteristic, which prevents the lathering of soap. This is due

to presence in water of certain salts of calcium, magnesium and other heavy metals

dissolved in it. A sample of hard water, when treated with soap (sodium or potassium salt

of higher fatty acid like oleic, palmitic or stearic) does not produce lather, but on the

other hand forms a white scum or precipiate. This precipitate is formed, due to the

formation of insoluble soaps of calcium and magnesium. Typical reactions of soap

(sodium stearate) with calcium chloride and magnesium sulphate are depicted as follows:

Thus, water which does not produce lather with soap solution readily, but forms a white

curd, is called hard water. On the other hand, water which lathers easily on shaking with

soap solution, is called soft water. Such water, consequently, does not contain dissolved

calcium and magnesium salts in it.

(1) Temporary or carbonate hardness is caused by the presence of dissolved

bicarbonates of calcium, magnesium and other heavy metals and the carbonate of iron.

Temporary hardness is mostly destroyed by mere boiling of water, when bicarbonates are

decomposed, yielding insoluble carbonates or hydroxides, which are deposited as a crust

at the bottom of vessel. Thus;

(2) Permanent or non-carbonate hardness is due to the presence of chlorides and

sulphates of calcium, magnesium, iron and other heavy metals. Unlike temporary

hardness, permanent hardness is not destroyed on boiling.

EQUIVALENTS OF CALCIUM CARBONATE:

The concentration of hardness as well as non-hardness constituting ions are, usually

expressed in terms of equivalent amount of CaCO3, since this mode pemlits the

multiplication and division of concentration, when required. The choice of CaCO3 in

particular is due to its molecular weight is 100 (equivalent weight = 50) and moreover, it

is the most insoluble salt that can be precipitated during water treatment.

UNITS OF HARDNESS:

(1) Parts per million (ppm) is the parts of calcium carbonate equivalent per 106 parts of

water, i.e., 1 ppm = 1 part of CaCO3 eq. hardness in 106 parts of water.

(2) Milligrams per liter (mg/L) are the number of milligrams of CaCO3 equivalent

hardness present per liter of water. Thus;

1 mg/L = 1 mg of CaCO3 eq. hardness of 1 L of water

But 1 L of water weighs

= 1 kg = 1,000 g = 1,000 x 1,000 mg = 106 mg.

. . . 1mg/L = 1 mg of CaCO3 eq. per 106 mg of water.

= 1 part of CaCO3 eq. per 106 parts of water = 1 ppm

(3) Clarke's degree (oCI) is number of grains (l/7000 1b) of CaCO3 equivalent hardness

per gallon (10lb) of water. Or it is parts of CaCO3 equivalent hardness per 70,000 parts of

water. Thus:

lo Clarke = 1 grain of CaC03 eq. hardness per gallon of water.

1o CI= 1 part of CaC03 eq. hardness per 70,000 parts of water.

(4) Degree French (oFr) is the parts of CaCO3 equivalent hardness per 105 parts of water.

Thus:

1o Fr = 1 part of CaCO3 hardness eq. per 105 parts of water.

(5) Mille equivalent per liter (meq/L) is the number of mill equivalents of hardness

present per liter. Thus;

1 meq/L = 1 meq of CaCO3 per L of water

= 10-3 x 50 g of CaCO3 eq. per liter

= 50 mg of CaCO3 eq. per liter

= 50 mg/L of CaCO3 eq. = 50 ppm.

Relationship between various units of hardness:

1 ppm = 1 mg/L = 0.1o Fr = 0.07'oCl = 0.02 meq/L

1 mg/L =1 ppm = 0.1o Fr = 0.1o Fr = 0.02 meq/L

1o Cl = 1.433o Fr = 14.3 ppm = 14.3 mg/L = 0.286 meq/L

1o Fr = 10 ppm =10 mg/L =0.07o Cl = 0.2 meq/L

1meq/L = 50 mg/L =50ppm = 5o Fr = 0.35o Cl

DISADVANTAGES OF USING HARD WATER IN BOILERS:

(a) Scale and sludge formation in boilers

In boilers, water evaporates continuously and the concentration of the dissolved salts

increases progressively. When their concentrations reach saturation point, they are

thrown out of water in the form of precipitates on the inner walls of the boiler. If the

precipitation takes place in the form of loose and slimy precipitate, it is called sludge. On

the other hand, if the precipitated matter forms a hard, adhering crust/coating on the inner

walls of the boiler, it is called scale.

Sludge is a soft, loose and slimy precipitate formed within the comparatively colder

portions of the boiler and collects in areas of the system, where the flow rate is slow or at

bends. Sludge’s are formed by substances which have greater solubility in hot water than

in cold water, e.g., MgCO3, MgCl2, CaCl2, MgSO4, etc.

Disadvantages of sludge formation :

1. Sludges are poor conductor of heat, so they tend to waste a portion of heat

generated.

2. If sludges are formed along with scales, then former gets entrapped in the

latter and both get deposited as scales.

3. Excessive sludge formation disturbs the working of the boiler. It settles in the

regions of poor water circulation such as pipe connection, plug opening,

gauge-glass connection, thereby causing even choking of the pipes.

Prevention of sludge formation :

(1) By using well softened water, (2) By frequently ‘blow-down operation’, i.e., drawing

off a portion of the concentrated water. Scales are hard deposits, which stick very firmly

to the inner surfaces of the boiler. Scales are difficult to remove, even with the help of

hammer and chisel. Scales are the main source of troubles. Formation of scales may be

due to;

(1) Decomposition of calcium bicarbonate

Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2 ↑

Scale

However, scale composed chiefly of calcium carbonate is soft and is the main cause of

scale formation in low-pressure boilers. But in high-pressure boilers, CaCO3 is soluble.

CaCO3 + H2O → Ca(OH2)2 (soluble) + CO2 ↑

Deposition of calcium sulphate :

The solubility of calcium sulphate in water decreases with rise of temperature. Thus,

solubility of CaSO4 is 3,200 ppm at 15oC and it reduces to 55 ppm at 230oC and 27 ppm

at 320oC. In other words, CaSO4 is soluble in cold water, but almost completely insoluble

in super-heated water. Consequently, CaSO4 gets precipitated as hard scale on the heated

portions of the boiler. This is the main cause of scales in high-pressure boilers. Calcium

sulphate scale is quite adherent and difficult to remove even with the help of hammer and

chisel.

(1) Hydrolysis of magnesium salts: Dissolved magnesium salts undergo hydrolysis (at

prevailing high temperature inside the boilers) footing magnesium hydroxide precipitate,

which forms a soft type of scale e.g.,

MgCl2 + 2 H2O → Mg(OH)2 ↓ + 2HCl ↑

(2) Presence of silica (SiO2), even present in small quantities, deposits as calcium

silicate (CaSiO3) and/ or magnesium silicate (MgSiO3). These deposits stick very firmly

on the inner side of the boiler surface and are very difficult to remove. One important

source of silica in water is the sand filter.

Disadvantages of scale formation :

(1) Wastage of fuel : Scales have a low thermal conductivity, so the rate of

heat transfer from boiler to inside water is greatly decreased. In order to

provide a steady supply of heat to water, excessive or over heating is

carried out and this causes increase in fuel consumption. The wastage

depends upon the thickness and the nature of scale:

Thickness of scale (mm) 0.325 0.625 1.25 2.5 12

Wastage of fuel 10% 15% 50% 80% 150%

(2) Lowering of boiler safety: Due to scale formation, over-heating of boiler is

to be done in order to maintain a constant supply of steam. The over-heating of the

boiler tube makes the boiler material softer and weaker and this causes distortion

of boiler tube and makes the boiler unsafe to bear the pressure of the steam,

especially in high-pressure boilers.

(3) Decrease in efficiency: Scales may sometimes deposit in the valves and

condensers of the boiler and choke them partially. Tills results in decrease in

efficiency of boiler.

(4) Danger of explosion: When thick scales crack, due to uneven expansion, the

water comes suddenly in contact with over-heated iron plates. This causes

formation of a large amount of steam suddenly. So sudden high-pressure is

developed, which may even cause explosion of the boiler.

Removal of scales:

(i) With the help of scraper or piece of wood or wire brush, if they are loosely

adhering.

(ii) (ii) By giving thermal shocks (i.e., heating the boiler and then suddenly cooling

with cold water), if they are brittle.

(iii) By dissolving them by adding them chemicals, if they are adherent and hard.

Thus, calcium carbonate scales can be dissolved by using 5-10% HCl. Calcium

sulphate scales can be dissolved by adding EDTA (ethylene diamine tetra

acetic acid), with which they form soluble complexes.

(iv) By frequent blow-down operation, if the scales are loosely adhering.

Prevention of scales formation:

(1) External treatment includes efficient 'softening of water’ (i.e. removing hardness

producing constituents of water).

(2) Internal treatment: In this process (also called sequestration), an ion is prohibited

to exhibit its original character by 'complexing’ or converting it into other more

soluble salt by adding appropriate reagent. An internal treatment is accomplished by

adding a proper chemical to boiler water either : (a) to precipitate the scale forming

impurities in the form of sludges, which can be removed by blow-down operation, or

(b) to convert them into compounds, which will stay in dissolved form in water and

thus do not cause any harm.

Internal treatments methods are, generally, followed by 'blow-down operation', so that an

accumulated sludge is removed. Important internal conditioning/treatment methods are;

(i) Colloidal conditioning: In low-pressure boilers, scale formation can be avoided by

adding organic substances like kerosene, tannin, agar-agar (a gel), etc., which get coated

over the forming precipitates, thereby yielding non-sticky and loose deposits, which can

easily be removed by pre-determined blow-down operations.

(ii) Phosphate conditioning: In high-pressure boilers, scale formation can be avoided by

adding sodium phosphate, which reacts with hardness of water forming non-adherent and

easily removable, soft sludge of calcium and magnesium phosphates, which can be

removed by blow - down operation, e.g.,

3CaCl2 + 2Na3PO4 → Ca3(PO4)2 + 6 NaCl

The main phosphates employed are : (a) NaH2PO4, sodium dihydrogen phosphate

(acidic); (b) Na2HPO4, disodium hydrogen phosphate (weakly alkaline); (c) Na3PO4,

trisodium phosphate (alkaline).

(iii) Carbonate conditioning: In low-pressure boilers, scale-formation can be avoided

by adding sodium carbonate to boiler water, when CaSO4 is converted into calcium

carbonate in equilibrium.

CaSO4 +Na2CO3 → CaCO3 + Na2SO4

Consequently, deposition of CaSO4 as scale does not take place and calcium is

precipitated as loose sludge of CaCO3, which can be removed by blow-down operation.

(iv) Calgon conditioning: It involves adding calgon [sodium hexameta phosphate

(NaPO3)6 to boiler water. It prevents the scale and sludge formation by forming soluble

complex compound with CaSO4.

Na2[Na4(PO3)6] → 2 Na+ + [Na4P6O18]2-

Calgon

2 CaSO4 + [Na4P6O18]2 − → [Ca2P6O18]2 − + 2 Na2SO4

Soluble complex ion

(v) Treatment with sodium aluminates (NaAlO2): Sodium aluminates gets

hydrolyzed yielding NaOH and a gelatinous precipitate of aluminium hydroxide.

NaAlO2 + 2H2O → NaOH + Al(OH)3

Sodium meta-aluminate Gelatinous precipitation

The sodium hydroxide, so-formed, precipitates some of the magnesium as Mg(OH)2 ,

MgCl2 + 2NaOH → Mg(OH)2 + 2 NaCI

The flocculent precipitate of Mg(OH)2 plus Al(OH)3, produced inside the boiler, entraps

finely suspended and colloidal impurities, including oil drops and silica. The loose

precipitate can be removed by pre-determined blow-down operation.

(vi) Electrical conditioning: Sealed glass bulbs, containing mercury connected to a

battery, are set rotating in the boiler. When water boils, mercury bulbs emit electrical

discharges, which prevents scale forming particles to adhere /stick together to form scale.

(vii) Radioactive conditioning: Tablets containing radioactive salts are placed inside the

boiler water at a few points. The energy radiations emitted by these salts prevent scale

formation.

(viii) Complex metric method: It involves addition of 1.5 % alkaline (pH = 8.5) solution

of EDTA to feed-water. The EDTA binds to the scale-forming cations to form stable and

soluble complex. As a result, the sludge and scale formation in boiler is prevented.

Moreover, this treatment : (1) prevents the deposition of iron oxides in the boiler, (2)

reduces the carryover of oxides with steam, and (3) protects the boiler units from

corrosion by wet steam (steam containing liquid water).

(b) CAUSTIC EMBRITTLEMENT:

Caustic embrittlement is a type of boiler corrosion, caused by using highly alkaline water

in the boiler. During softening process by lime-soda process, free Na2CO3 is usually

present in small proportion in the softened water. In high pressure boilers,

Na2CO3 decomposes to give sodium hydroxide and carbon dioxide,

Na2CO3 + H2O → 2NaOH + CO2

and this makes the boiler water basic ["caustic"]. The NaOH containing water flows into

the minute hair-cracks, always present in the inner side of boiler, by capillary action.

Here, water evaporates and the dissolved caustic soda concentration increases

progressively. This caustic soda attacks the surrounding area, thereby dissolving iron of

boiler as sodium ferroate this causes embrittlement of boiler parts, particularly stressed

parts (like bends, joints, rivets, etc.), causing even failure of the boiler.

Caustic embrittlement can be avoided :

1. by using sodium phosphate as softening agent, instead of sodium carbonate ;

2. by adding tannin or lignin to boiler water, since these blocks the hair-cracks,

thereby preventing infiltration of caustic soda solution in these;

3. by adding sodium sulphate to boiler water. Na2SO4 also blocks hair-cracks,

thereby preventing infiltration of caustic soda solutions. It has been observed that

caustic cracking can be prevented, if Na2SO4 is added to boiler water so that the

ratio :

is kept as 1:1:2:1 and 3:1 in boilers working respectively at pressures up to 10, 20 and

above 20 atmospheres.

(c) BOILER CORROSION:

Boiler corrosion is decay of boiler material by a chemical or electro-chemical attack by

its environment. Main reasons for boiler corrosion are:

(1) Dissolved oxygen: Water usually contains about 8 ml of dissolved oxygen per litre at

room temperature. Dissolved oxygen in water, in presence of prevailing high

temperature, attacks boiler material:

2 Fe + 2H2O + O2 → 2 Fe(OH)2

4 Fe(OH)2 + O2 → 2 (Fe2O3.2H2O)

Ferrous hydroxide Rust

Removal of dissolved oxygen:

(1) By adding calculated quantity of sodium sulphite or hydrazine or sodium sulphide.

Thus;

2 Na2SO3 + O2 → 2 Na2SO4

N2H4 + O2 → N2 + 2 H2O

Hydrazine

Na2S + 2 O2 → Na2SO4

(2) By mechanical de-aeration, i.e., water spraying in a perforated plate-fitted tower,

heated from sides and connected to vacuum pump (see Fig. 2). High temperature, low

pressure and large exposed surface (provided by perforated plates) reduces the dissolved

oxygen in water

(2) Dissolved carbon dioxide : CO2 is carbonic acid, CO2 + H2O → H2CO3

which has a slow corrosive effect on the boiler material. Carbon dioxide is also released

inside the boiler, if water used for steam generation it contains bicarbonate, e.g.,

Mg(HCO3)2 → MgCO3 + H2O + CO2

Removal of CO2: (1) By adding calculated quantity of ammonia. Thus,

2NH4OH + CO2 → (NH4)2CO3 + H2O

(2) By mechanical-aeration process along with oxygen.

(3) Acids from dissolved salts: Water containing dissolved magnesium salts liberate

acids on hydrolysis, e.g.,

MgCl2 + 2H2O → Mg(OH)2 + 2HCl

The liberated acid reacts with iron (of the boiler) in chain like reactions producing HCI

again and again. Thus

Fe + 2HCI → FeCl2 + H2

FeCl2 + 2H2O → Fe(OH)2 + 2HCl

Consequently, presence of even a small amount of MgCl2 will cause corrosion of iron to

a large extent.

QUALITIES OF DRINKING (POTABLE) WAATER:

Drinking water is water intended for human consumption for drinking and cooking

purposes from any source. It includes water (treated or untreated) supplied by any means

for human consumption.

Drinking water quality standards describes the quality parameters set for drinking water.

Despite the truth that every human on this planet needs drinking water to survive and that

water may contain many harmful constituents, there are no universally recognized and

accepted international standards for drinking water. Even where standards do exist, and

are applied, the permitted concentration of individual constituents may vary by as much

as ten times from one set of standards to another.

Many developed countries specify standards to be applied in their own country. In

Europe, this includes the European Drinking Water Directive and in the United States

the United States Environmental Protection Agency (EPA) establishes standards as

required by the Safe Drinking Water Act. For countries without a legislative or

administrative framework for such standards, the World Health Organization publishes

guidelines on the standards that should be achieved. China adopted its own drinking

water standard GB3838-2002 (Type II) enacted by Ministry of Environmental

Protection in 2002.

Where drinking water quality standards do exist, most are expressed as guidelines or

targets rather than requirements, and very few water standards have any legal basis or, are

subject to enforcement.[5] Two exceptions are the European Drinking Water Directive and

the Safe Drinking Water Act in the USA, which require legal compliance with specific

standards.

INDIAN STANDARDS FOR DRINKING WATER: Drinking water shall comply

with the requirements given in Tables 1 to 6. Drinking water shall also comply with

bacteriological requirements, virological requirements and biological requirements.

Table 1: Organoleptic and Physical Parameters

Table 2 General Parameters Concerning Substances Undesirable in Excessive

Amounts

Table 3 Parameters Concerning Toxic Substances

Table 4 Parameters Concerning Radioactive Substances

Table 5 Pesticide Residues Limits

Table 6 Bacteriological Quality of Drinking Water