Electrochemistry - DPG PolytechnicElectrolysis of aqueous copper sulphate solution (using pt...
Transcript of Electrochemistry - DPG PolytechnicElectrolysis of aqueous copper sulphate solution (using pt...
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