Download 1. What are micelles? Give two examples of micellar systems. Sol. A

1. What are micelles? Give two examples of micellar systems.
Sol. A micelleis an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in
aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding
solvent, sequestering the hydrophobic single-tail regions in the micelle centre. This phase is caused
by the packing behavior of single-tailed lipids in a bilayer. The difficulty filling all the volume of the
interior of a bilayer, while accommodating the area per head group forced on the molecule by the
hydration of the lipid head group, leads to the formation of the micelle. This type of micelle is known
as a normal phase micelle (oil-in-water micelle). Inverse micelles have the head groups at the centre
with the tails extending out (water-in-oil micelle).
b. Explain racemic modefication.
Sol. In chemistry, a racemic mixture, or racemate /re sime t/, is one that has equal amounts of leftand right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic
acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.
A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix dl- may be used), indicating
an equal (1:1) mixture of dextro and levo isomers. Also the prefix rac- (or racem-) or the symbols RS
and SR (all in italic letters) are used.
c. Give all stereoisomers of 2,3-dichloro butane. identify the mesoform.
Sol.
.
d. Twoisomeric compounds A and B having the molecular formula C5H8 absorb at lambda max 223
nm and 178 nm. Write the structures of the isomers.
Sol.
e. Describe inductive effect and electromeric effect with suitable examples.
Sol. the 'Inductive Effect' is an experimentally observable effect of the transmission of charge through
a chain of atoms in a molecule. The net polar effect exerted by a substituent is a combination of this
inductive effect and the mesomericeffect.the 'Inductive Effect' is an experimentally observable effect
of the transmission of charge through a chain of atoms in a molecule. The net polar effect exerted by
a substituent is a combination of this inductive effect and the mesomeric effect.
Electromeric effect refers to a molecular polarizability effect occurring by an intramolecular electron
displacement (sometimes called the ‘conjugative mechanism’ and, previously, the ‘tautomeric
mechanism’) characterized by the substitution of one electron pair for another within the same atomic
octet of electrons.The addition of acids to alkenes is an example of the +E effect. After the transfer
takes place, the reagent gets attached to the atom where the electrons have been transferred to.
f. What is calgon conditioning? Explain.
Sol. Calgon is a brand registered trademark of different corporations. The original product consisted
of powdered sodium hexametaphosphate (amorphous sodium polyphospate), which in water would
complex with ambient calcium ion and certain other cations, preventing formation of unwanted salts
and interference by those cations with the actions of soap or other detergents. calgon conditioning is
better than phosphate conditioning because it forms a water soluble complex Na2[Ca2(PO3)6] and
does not form even scales.
g. (i) Water recovery
Water recovery projects can provide additional water for productive and environmental purposes.
The volumes of water saved are in addition to water provided for water users and the environment
through the rules in the water sharing plans.
Water recovery can be achieved through investing in infrastructure to achieve greater efficiency and
through the purchase of water licences.
(ii) Solute rejection
Rejection Coefficient
• Solutes retained by the membrane
– Lower solubility in water or
– Diffuse more slowly through the membrane
• Rejection coefficient
Cpi= conc. of solute i in permeate
Cri= conc. of solute i in retentate
Rejection Coefficient
• Ranges:
– 1–0
• When ri=0
– the membrane is completely permeable
• When ri= 0
– the membrane is completely impermeable
h. Discuss the structure of methyl free radical.
Sol. Methyl radical is a trivalent radical derived from methane, produced by the ultraviolet
disassociation of halomethanes.
It can also be produced by the reaction of methane with the hydroxyl radical:
OH• + CH4 → CH3• + H2O
The molecular geometry of the methyl radical is quasi-trigonal planar, although the energy cost of
distortion to a pyramidal geometry is small. Substitution of hydrogen atoms by more electronegative
substituents leads to radicals with a pyramidal geometry, such as the trifluoromethyl radical, CF3.
i. What is Langelire Index (LI)? Mention its significance.
Sol. This calculator helps you determine the scaling potential of the water by using the Langelier
Saturation Index.
LSI
Indication
LSI<0 Water is undersaturated with respect to calcium carbonate. Undersaturated water has a
tendency to remove existing calcium carbonate protective coatings in pipelines and equipment.
LSI=0 Water is considered to be neutral. Neither scale-forming nor scale removing.
LSI>0 Water is supersaturated with respect to calcium carbonate (CaCO3) and scale forming may
occur.
3.(a) Basic principle of NMR:The nuclei of all elements carry a charge. When the spins of the
protons and neutrons comprising these nuclei are not paired, the overall spin of the charged nucleus
generates a magnetic dipole along the spin axis, and the intrinsic magnitude of this dipole is a
fundamental nuclear property called the nuclear magnetic moment, µ. The symmetry of the charge
distribution in the nucleus is a function of its internal structure and if this is spherical (ie analogous to
the symmetry of a 1s hydrogen orbital), it is said to have a corresponding spin angular momentum
number of I=1/2, of which examples are 1H, 13C, 15N, 19F, 31P etc. Nuclei which have a non-spherical
charge distribution (analogous to e.g. a hydrogen 3d orbital) have higher spin numbers (eg10B, 14N
etc)
In quantum mechanical terms, the nuclear magnetic moment of a nucleus can align with an externally
applied magnetic field of strength Bo in only 2I+1 ways, either re-inforcing or opposing Bo. The
energetically preferred orientation has the magnetic moment aligned parallel with the applied field
(spin +1/2) and is often given the notation , whereas the higher energy anti-parallel orientation (spin
-1/2) is referred to as . The rotational axis of the spinning nucleus cannot be orientated exactly
parallel (or anti-parallel) with the direction of the applied field Bo (defined in our coordinate system as
about the z axis) but must precess about this field at an angle (for protons about with an angular
velocity given by the expression;
For a single nucleus with I=1/2 and positive
, only one transition is possible ( I=1, a single quantum
transition) between the two
energy levels;
NMR is all about how to
interpret such transitions in
terms of chemical structure.
We will first consider the
energy of a typical NMR
transition. If angular velocity
is related to frequency by o
= 2¼ , then
Chemical Shifts in NMR SpectraThe signal frequency that is detected in nuclear magnetic
resonance (NMR) spectroscopy is proportional to the magnetic field applied to the nucleus.
This would be a precisely determined frequency if the only magnetic field acting on the
nucleus was the externally applied field. But the response of the atomic electrons to that
externally applied magnetic field is such that their motions produce a small magnetic field at
the nucleus which usually acts in opposition to the externally applied field. This change in the
effective field on the nuclear spin causes the NMR signal frequency to shift. The magnitude of
the shift depends upon the type of nucleus and the details of the electron motion in the nearby
atoms and molecules. It is called a "chemical shift". The precision of NMR spectroscopy
allows this chemical shift to be measured, and the study of chemical shifts has produced a
large store of information about the chemical bonds and the structure of molecules.
the chemical shift is usually indicated by a symbol
reference.
which is defined in terms of a standard
N neighboring protons with the same coupling constant J will split the absorbance of a proton or set
of equivalent protons into N+1 lines. Note that the splitting pattern observed for a particular proton or
set of equivalent protons is not due to anything inherent to that nucleus but due to the influence of the
neighboring protons. The relative intensity ratios are given by Pascal's triangle as shown in .
3(b)C3H6O :For aldehyde CH3CH2CHO
Signals :a,b,cSpilitting pattern: a=Triplet
B= Quartet
C= Triplet
For Ketone:CH3COCH3
Signals : a,
Spilitting pattern: a = singlet
(c) (i)Group frequency region: Appears in between 4000-1400cm-1 The pattern of bands in the region
are typical of functional groups present in an organic compound.
(ii)Fingerprint region:
4.(a) Beer-Lambert law:
,
whereA iss the measure
ed absorbancce, in Absorba
ance Units (A
AU),
at a given
n wavelength,
is the intensity of th
he incident light
is the trans
smitted intenssity, L the patthlength throu
ugh the sample, and c the
concentra
ation of the ab
bsorbing speccies. For each
h species and
d wavelength, ε is a consta
ant known as
the molar absorptivity or
o extinction coefficient.
c
Th
his constant is
s a fundamen
ntal molecularr property in a
given solvvent, at a partticular temperrature and pre
essure, and has
h units of
o often
or
.
The absorrbance and extinction
e
ε are
e sometimes defined in terrms of the nattural logarithm
m instead of
the base-10 logarithm.The Beer-Lam
mbert Law is useful for cha
aracterizing m
many compou
unds but doess
a a universal relationship for the conce
entration and absorption
a
of all substance
es
not hold as
(b)λmax: When
W
a sample
e is exposed to light energ
gy that matche
es the energyy difference be
etween a
possible electronic
e
tran
nsition within the molecule, a fraction off the light energy would be absorbed byy
the moleccule and the electrons
e
would be promote
ed to the high
her energy sta
ate orbital. A spectrometerr
records th
he degree of absorption
a
byy a sample at different wavvelengths and
d the resulting
g plot of
absorbanc
ce (A) versuss wavelength (λ) is known a
as a spectrum
m. The wavele
ength at whicch the sample
absorbs th
he maximum amount of lig
ght is known a
as λmax. For ex
xample, show
wn below is th
he spectrum of
o
isoprene. Isoprene is colorless
c
as it does not abssorb light in th
he visible spectrum, and ha
as a λmax of
222nm.
e spectrum off isoprene sho
owing maximu
um absorption at 222 nm.
UV-visible
ε= ( σ × 6.023 × 1020)/2
2.303. Thus
A= ε × c × b
OR
A = εbc
Since we have used moles/liter
m
as the units of co
oncentration, ε stands for m
molar absorpttivity (or molar
extinction coefficient). If the units of concentration were g/liter then the ε wo
ould be replacced by “a”
(absorptivvity).
By definitiion, the molarr absorptivity (ε) at a speciified waveleng
gth of a substtance in soluttion is the
absorbanc
ce at that wavvelength of a 1 mole/liter ssolution of the
e substance in
n a cell having
g a path lengtth
of 1 cm. The
T units of molar
m
absorptivity are liter m
mole-1 cm-1
(c)intensiity of initial lig
ght =I0
Intensity after first tran
nsmission =I1 =60/100x I0
Intensity after second transmission =I2 =30/100xx I1
= 30/100
0x60/100 x I0
Required
d ratio (change
e in intesnsityy) =I2/I0
= 30/100 x 60/100 xI0 /I0
= 18/100 = 18%
5.(i)Mech
hanism :Fried
del-Crafts alkkylation only ccatalytic amou
unts of a Lewiis acid must be
b applied,
since the
e Lewis acid iss recovered during
d
the reaction by its re
elease from th
he reactants. The following
g,
in order of
o decreasing activity, are examples
e
of Lewis
L
acids th
hat are appro
opiate for application as a
catalyst in Friedel-Cra
afts alkylation::
,
,
,
,
,
and
.
Fig.1
1Formation of
o the polarizzed alkyl halide-Lewis ac
cid
com
mplex.
t electrophile that is atta
acked by the a
aromatic π ele
ectron system
m is the alkyl halide-Lewis
Usually, the
acid complex.
(ii)Cationic Polymerization
Initiation and Propagation:The mechanism of cationic polymerization is a kind of repetitive
alkylation reaction.
Electron donating groups are needed as the R groups because these can stabilize the propagating
species by resonance. Examples:
Propagation is usually very fast. Therefore, cationic vinyl polymerizations must often be run at low
temperatures. Unfortunately, cooling large reactors is difficult and expensive. Also, the reaction can
be inhibited by water if present in more than trace amounts, so careful drying of ingredients is
necessary (another expense).
Cationic Initiators:Proton acids with unreactive counterions
Lewis acid + other reactive compound:
(iii) Walden inversion: Walden inversion: The inversion of stereochemical configuration at a
stereocenter during a chemical reaction.
In the SN2 reaction between iodide ion and (S)-2-chlorobutane, backside attack by the nucleophile
causes Walden inversion. The product is (R)-2-iodobutane.
If the substrate under nucleophilic attack is chiral, this can lead, although not necessarily, to an
inversion of stereochemistry called a Walden inversion (the nucleophile attacks the electrophilic
carbon center, inverting the tetrahedron, much like an umbrella turning inside out in the wind).In an
example of the SN2 reaction, the attack of OH− (the nucleophile) on a bromoethane (the electrophile)
results in ethanol, with bromide ejected as the leaving group:
SN2 reaction of bromoethane with hydroxide ion.:SN2 attack occurs if the backside route of attack is
not sterically hindered by substituents on the substrate. Therefore this mechanism usually occurs at
an unhind
dered primary
y carbon centrre. If there is steric
s
crowdin
ng on the sub
bstrate near th
he leaving
group, suc
ch as at a terrtiary carbon centre,
c
the su
ubstitution will involve an SN1 rather than an SN2
mechanism, (an SN1 would
w
also be more likely in
n this case be
ecause a sufficiently stable
e carbocation
intermedia
ary could be formed).
f
6(a)(ii)
o change of a biological or
o chemical
(i) The Q10 temperaturre coefficient is a measurre of the rate of
system ass a consequence of increasing the temp
perature by 10
0 °C. There a
are many exam
mples where
the Q10 is used, one be
eing the calcu
ulation of the n
nerve conducction velocity and another being
b
g the contraction velocity of
o muscle fibrres. It can also
o be applied tto chemical re
eactions and
calculating
many othe
er systems.
The Q10 iss calculated as:
a
whereR iss the rate,T is
s the temperatture in Celsius degrees or kelvins.
Q10 is a unitless quantity, as it is the
e factor by wh
hich a rate cha
anges, and iss a useful wayy to express
erature depen
ndence of a process.For most
m
biologicall systems, the
e Q10 value is ~ 2 to 3.
the tempe
(b) T1 = 30+273=303K
3
K,
36 hrs
2 hrs=168hrss
7 days x 24
T2 = 5+
+273=
278K
K
K=1/t,k1=1/t1
K2=1/t2
=43.16KJ/mol
(c) Methyl acetate undergoes hydrolysis, in the presence of an acid (HCl, for example), to give acetic
acidand methyl alcohol.
H+CH3COOCH3 + H2O → CH3COOH + CH3OH
In the presence of an acid, this reaction should be of second order, since two molecules are
reacting.But, it is found to be first order. This may be explained in the following way :
The rate of the reaction is given bydx / dt = k’[CH3COOCH3] [ H2O ] ,
where k’ is the rate constant (or specific rate constant).
Since water is present in large excess, its active mass (molar concentration) virtually remains
constantduring the course of the reaction. Therefore, its active mass gets included in the constant,
and the aboveequation reduces to :
dx / dt = k1 [CH3COOCH3]
Hydrolysis using dilute alkali
This is the usual way of hydrolysing esters. The ester is heated under reflux with a dilute alkali like
sodium hydroxide solution.There are two big advantages of doing this rather than using a dilute acid.
The reactions are one-way rather than reversible, and the products are easier to separate.Taking the
same esters as above, but using sodium hydroxide solution rather than a dilute acid:First, hydrolysing
ethyl ethanoate using sodium hydroxide solution:
Hydrolysis of ester using alkali is second order reaction because mechanism involves NaOH in first
step forms transition state.
7.(a )
t1/2/2 t1/2
n-1
n-1
= 1/(ao )/1/(2ao )
½ =2n-1 ,n-1=-1,n=0
Thus the reaction is zero order.
(b) NUMBER AVERAGE MOLECULAR WEIGHT Number average molecular weightThe number
average molecular weight is a way of determining the molecular weight of a polymer. Polymer
molecules, even ones of the same type, come in different sizes (chain lengths, for linear
polymers
s), so the ave
erage molecu
ular weight w
will depend on
o the metho
od of averagiing. The
number average
a
mole
ecular weigh
ht is the ordin
nary arithme
etic mean or average of th
he molecular
weights of
o the individ
dual macrom
molecules. It iis determine
ed by measurring the mole
ecular weigh
ht
of n polym
mer moleculles, summing
g the weights, and dividing by n.
Weight av
verage mole
ecular weightt
The weight average molecular
m
we
eight is a wayy of describing
g the molecular weight of a polymer.
Polymer molecules,
m
evven if of the sa
ame type, com
me in differen
nt sizes (chain
n lengths, for linear
polymers)), so we have
e to take an av
verage of som
me kind. For the
t weight ave
erage molecu
ular weight,
this is calcculated by
where
er of molecule
es of molecula
ar weight
is the numbe
The ratio of the weigh
ht average to
o the numberr average is called the
polydispe
ersityindex.T
Theweight-avverage molecu
ular weight, Mw, is also rela
ated to the fra
actional
monomerr conversion, p,
p in step-gro
owth polymerizzation as per Carothers' eq
quation:
c.
= 18.18 x 103
=
55000
sion is the grradual destrucction of materrials, (usually metals), by cchemical reacction with its
8.aCorros
environme
ent.In the most common use of the worrd, this meanss electrochem
mical oxidation
n of metals in
reaction with
w an oxidan
nt such as oxyygen. Rusting
g, the formatio
on of ironoxid
des, is a well-kknown
example of
o electrochem
mical corrosio
on. This type of damage tyypically producces oxide(s) or
o salt(s) of
the origina
al metal. Corrrosion can alsso occur in materials otherr than metals, such as cera
amics or
polymers,, although in this
t
context, the term degra
adation is mo
ore common. Corrosion degrades the
useful pro
operties of ma
aterials and sttructures inclu
uding strength
h, appearancce and permea
ability to
liquids and gases.Many structural alloys corrode merely from exposure to moisture
m
in aiir, but the
process can
c be stronglly affected byy exposure to certain substtances.
b.Electrochemical Corrosion Theory:
Electrochemical corrosion involves two half-cell reactions; an oxidation reaction at the anode and a
reduction reaction at the cathode. For iron corroding in water with a near neutral pH, these half cell
reactions can be represented as:
Anode reaction: 2Fe => 2Fe2+ + 4eCathode reaction: O2 + 2H2O + 4e- => 4OHThere are obviously different anodic and cathodic reactions for different alloys exposed to various
environments. These half cell reactions are thought to occur (at least initially) at microscopic anodes
and cathodes covering a corroding surface. Macroscopic anodes and cathodes can develop as
corrosion damage progresses with time.
From the above theory it should be apparent that there are four
fundamental components in an electrochemical corrosion cell:
•
•
•
•
An anode.
A cathode.
A conducting environment for ionic movement (electrolyte).
An electrical connection between the anode and cathode for
the flow of electron current.
If any of the above components is missing or disabled, the electrochemical corrosion process will be
stopped. Clearly, these elements are thus fundamentally important for corrosion control.
c.Corrosion Inhibitors: A corrosion inhibitor is a chemical compound that, when added to a liquid or
[1]
gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a
corrosion inhibitor depends on fluid composition, quantity of water, and flow regime. A common
mechanism for inhibiting corrosion involves formation of a coating, often a passivation layer, which
prevents access of the corrosive substance to the metal. Permanent treatments such as chrome
plating are not generally considered inhibitors, however. Instead corrosion inhibitors are additives to
the fluids that surround the metal or related object.
The nature of the corrosive inhibitor depends on (i) the material being protected, which are most
commonly metal objects, and (ii) on the corrosive agent(s) to be neutralized. The corrosive agents are
generally oxygen, hydrogen sulfide, and carbon dioxide. Oxygen is generally removed by reductive
inhibitors such as amines and hydrazines:
O2 + N2H4 → 2 H2O + N2
In this example, hydrazine converts oxygen, a common corrosive agent, to water, which is generally
benign. Related inhibitors of oxygen corrosion are hexamine, phenylenediamine, and
dimethylethanolamine, and their derivatives. Antioxidants such as sulfite and ascorbic acid are
sometimes used
9a.
b.Efficiency of fuel cell = nFE/-H
= 3.47
c.
10a.The catalytic reaction that depends upon the structure of pores of the catalyst and the size of the
reactant and product molecules is called shape/selective catalysis. Zeolites are good shape/selective
catalysts because of their honeycomb-like structures. Zeolites are aluminosilicates i.e., three
dimensional network silicates in which some silicon atoms are replaced by aluminium atoms. They
are found in nature as well as synthesized for catalytic selectivity. Zeolites, before using as catalysts,
are heated in vacuum so that the water of hydration is lost. As a result, zeolite becomes porous i.e.,
the cavities in the cage-like structure which were occupied by the water molecules become vacant.
The size of the pores generally varies between 260 pm and 740 pm. Thus only those molecules can
be adsorbed in these pores whose size is small enough to enter these cavities and also leave easily.
The reactions taking place in zeolites depend upon the size and shape of reactant and product
molecules as well as upon the pores and cavities of the zeolites. That is why these types of reactions
are called ‘shape-selective catalysis’ reactions.
Zeolites are being very widely used as catalysts in petrochemical industries for cracking of
hydrocarbons and isomerisation.
(i)
(ii)
(iii)
ZSM-5: An important zeolite catalyst used in the petroleum industry is ZSM-5. It converts
alcohols directly into gasoline (petrol) by dehydrating them so that a mixture of
hydrocarbons in formed.
BiMoO4: Prop-2-enal used to be prepared by reaction of oxygen with propene over a
BiMoO4 catalyst:
CH3CH=CH2 + O2 --> CH2=CHCHO + H2O
Ziegler-Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes (αolefins). Three types of Ziegler-Natta catalysts are currently employed:
Solid and supported catalysts based on titanium compounds. They are used in
polymerization reactions in combination with cocatalysts, organoaluminum compounds
such as triethylaluminium, Al(C2H5)3.Metallocene catalysts, combination of various mono-
and bis-metallocene complexes of Ti. Zr or Hf. They are usually used in polymerization
reactions in combination with a different organoaluminumcocatalyst, methylaluminoxane
(or methylalumoxane. MAO).
b. The valence bond theory was proposed by Heitler and London to explain the formation of
covalent bond quantitatively using quantum mechanics. Later on, Linus Pauling improved this theory
by introducing the concept of hybridization.
The main postulates of this theory are as follows:
* A covalent bond is formed by the overlapping of two half filled valence atomic orbitals of two
different atoms.
* The electrons in the overlapping orbitals get paired and confined between the nuclei of two atoms.
* The electron density between two bonded atoms increases due to overlapping. This confers stability
to the molecule.
* Greater the extent of overlapping, stronger is the bond formed.
* The direction of the covalent bond is along the region of overlapping of the atomic orbitals i.e.,
covalent bond is directional
c.
Electrons are not always shared equally between two bonding atoms; one atom might exert more of a
force on the electron cloud than the other. This "pull" is termed electronegativity and measures the
attraction for electrons a particular atom has. The unequal sharing of electrons within a bond leads to
the formation of an electric dipole: a separation of positive and negative electric charge. Partial
charges are denoted as δ+ (delta plus) and δ− (delta minus). Atoms with high electronegativities —
such as fluorine, oxygen, and nitrogen — exert a greater pull on electrons than atoms with lower
electronegativities. In a bond, this can lead to unequal sharing of electrons between atoms, as
electrons will be drawn closer to the atom with the higher electronegativity.
The hydrogen fluoride, HF, molecule is polar by virtue of polar covalent bonds — in the covalent bond
electrons are displaced towards the more electronegative fluorine atom