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Q1. Haloalkanes undergo
nucleophilic substitution whereas
haloarenes undergo electrophilic
substitution.WHY?
Ans 1. Haloalkanes are more polar than
haloarenes.Consequently the carbon atom carrying the
halogen in haloalkane is more electron deficient than that
in haloarenes.As the result halalkane undergo
nucleophilic substitution more readily than haloarenes.
In contrast haloarenes contain a benzene ring.since the
typical reaction of benzene are electrophilic
substitution,therefore haloarenes undergo electrophilic
substitution.
Q2. Explain why alkyl
halides,though polar,are immiscible
with water?
Ans2. Alkyl halide are polar molecules, therefore,their
molecules are held together by dipole-dipole
attraction.The molecules of water are held together by H
bonds.Since the new force of attraction between water
and alkyl halide molecules are weaker than the force of
attraction already existing between alkyl halide-alkyl
halide molecule and water-water molecules.Thus alkyl
halide are immiscible with water.
Q3. What happens when chlorine is
passed through boiling toluene in
the presence of sunlight?
Ans 3. Free radical substitution
occurs at the METHYL group giving
first benzyl chloride, then benzal
dichloride and finally
benzotrichloride.
Q4. Which is stronger acid phenol or
cresol?
Ans 4. Due to the I+ effect of CH3 grp
electron –density in the O-H bond
increases.Thus it becomes difficult to
break the O-H bond as compared to
that of the phenol & hence cresol is
more acidic than phenol.
Q5. Why gridnard reagent soluble in
ether but not in benzene?
Ans 5. Gridnard reagent form
coordination complexes with ether
but not with benzene since the
ether has lone pairs of electron but
the benzene does not.
Q6. What makes ethanoic acid more
stronger than ethanol.
Ans 6. Ethanoate ion obtained by
loss of proton from ethanoic acid is
stabilized by resonance but ethoxide
ion obtained by loss of proton from
ethanol is not.This makes ethanoic
acid more stronger than ethanol.
Q7. Aniline gets coloured on standing in
air for a long time WHY?
Ans 7. Due to the strong electron
donating effect (+R-effect) of NH2
grp, the electron density on benzene
ring increases. As a result, aniline is
easily oxidised on standing in air for
long time to form coloured
products.
Q8. Why do nitro compounds have high
boiling point in comparison with other
compounds of same molecular mass?
Ans 8. Nitro compounds have high
dipole moments and thus have
strong dipole-dipole
interaction.Therefore ,their boiling
points are much higher as compared
to hydrocarbons or other
compounds of same molecular mass.
Q9. Why is carbon nitro bond length in
aromatic amines shorter than the
aliphatic amines?
Ans 9. Due to the electron donating resonance
effect of NH2 grp the carbon nitrogen bond in the
aromatic amines has some double bond
character.
In contrast in the aliphatic amines the
carbon –nitrogen bond has only single bond
character therefore carbon-nitrogen bond length
in aromatic amines is shorter than in aliphatic
amines.
Q10. Why do amines act as
nucleophiles?
Ans 10. Due to the presence of lone
pair of electron on the Natom,amines can easily donate this
lone pair to the carbon species and
hence act as nucleophiles.
Q.11) p-Dichlorobenzene has high
melting point & lower solubility
than ortho and meta isomers.
Discuss.
symmetrical fits closely in the crystal
lattice & thus ha stronger intermolecular
forces of attraction than o- & m- isomers.
As during melting or dissolution, the
crystal lattice breaks. therefore, large
amount of energy is needed to melt or
dissolve the p-isomer than the
corresponding o-and m-isomers. In other
words, the melting point of the p-isomer is
higher and its solubility lower than the
corresponding o-and m-isomers.
Q.12)The treatment of alkyl
chlorides with aqueous KOH leads to
the formation of alcohols but in
presence of alcoholic KOH, alkenes
are the major products. Explain
why?
ANS: In aqueous solution, KOH is almost completely
ionized to give OH- ions which being a strong nucleophile
brings about a substitution reaction on alkyl halides to
form alcohols. In the aqueous solution, OH- ions are
highly solvated (hydrated). This reduces the basic
character of OH- ions which fail to abstract hydrogen from
the β-carbon of the alkyl chloride to form an alkenes.
On the other hand, and alcoholic solution of KOH
contains alkoxide (RO-) ions which being a much stronger
base than OH- ions preferentially eliminates a molecule of
HCI from an alkyl chloride to form alkenes.
Q13.
Explain the following in one or
two sentences :
(i)Allyl chloride is hydrolysed more
readily than n-propyl chloride.
(ii)Vinyl chloride is hydrolysed more
slowly than ethyl chloride.
ANS : (i)Allyl chloride readily undergoes ionization to produce resonance stabilized allyl
carbocation. Since carbocations are reactive species, therefore, allyl cation readily combines
with OH- ions to form allyl alcohol.
CH2=CH-CH2-Cl
CH2=CH-CH2-OH
CH2=CH-CH2+ + ClCH2+-CH= CH2
On the other hand, n-propyl chloride does not undergo ioization to produce n-propyl
carbocation and hence allyl chloride is hydrolysed more readily that n-propyl chloride.
(ii)Vinyl chloride may be represented as a resonance hybrid of the following two structures:
CH2=CH-Cl
CH2- -CH=Cl+
As a result of resonance, the carbon-chlorine bond acquires some double bond character. On
the other hand, in ethyl chloride, the carbon-chlorine bond is a pure single bond. Thus, vinyl
chloride undergoes hydrolysis more slowly that ethyl chloride.
Q14. Haloalkanes react with KCN
to form alkyl cyanides as main
product while AgCN form isocyanides
as the chief product. Explain.
ANS :KCN is predominantly ionic and provides
cyanide ions in solution. However both carbon
and nitrogen atoms are in a position to donate
electron pairs, the attack takes place mainly
through carbon atom and not through nitrogen
atom since C-C bond is more stable the C-N bond.
However, AgCN is mainly covalent in nature and
nitrogen is free to donate electron pair forming
isocyanide as the main product.
Q15.
Account for the following:
Haloalkanes undergo nucleophilic
substitution whereas haloarenes
undergo electrophilic substitutions.
ANS :
Haloalkanes are more polar than
haloarenes. As a result the carbon atom carrying the
halogen in halolkanes is more electron-deficient than
that in haloarenes. Consequently, haloalkanes
undergo nucleophilic substitutions more readily than
haloarenes.
On the other hand, haloarenes contain a
benzene ring. Since the typical reaction of benzene
are electrophilic substitutions, therefore, haloarenes
undergo electrophilic substitutions while haloalkanes
which do not contain a benzene ring to not undergo
electrophilic substitutions.
Q16. Explain
why propanol has higher boiling
point
than that of the hydrocarbon,
butane ?
ANS : The molecules of butane are
held together by weak van der Waal’s
forces of attraction while those of
propanol are held together by stronger
intermolecular hydrogen bonding.
Hence, the boiling point of propanol is
much higher that that of butane.
Q17. Alcohols are comparatively
more soluble in water than
hydrocarbons of comparable
molecular masses. Explain this fact.
ANS : Alcohols can form H-bonds
with water and break the H-Bonds
already existing between water
molecules. Hence, they are soluble in
water.
In contrast, hydrocarbons cannot form
H-bonds with water and hence are
insoluble in water.
Q18.Lower alcohols are soluble in
water, higher alcohols are not, why?
ANS :Lower alcohols can form Hbonds with water whereas higher
alcohols cannot due to large
hydrocarbons part.
Q19. Ortho-nirophenol is more
acidic than ortho-methoxyphenol.
Why?
ANS : It is because Nitro group is
electron withdrawing which
increases the acidic character
whereas –OCH3 group is electron
releasing which decreases acidic
character.
Q20. Phenol has smaller dipole
moment than methanol.
OR
Why are dipole moments of phenols
smaller that dipole moments of
alcohols.
ANS : Due to electron withdrawing
effect of the benzene ring the C-O
bond in phenol is less polar but in
case of methanol due to electrondonating effect of CH3 group, C-O
bond is more polar.
Q21]
Why does H2 is liberated at cathode
during kolbes electrolytic reaction?
Ans]
During Kolbes electrolytic reaction
hydrogen gas is liberated at cathode
+
because discharge potential of H
+
ions is lower than that of Na ions,
therefore H+ ions are discharged to
produce H2 while Na+ ions remains in
the solution .
Q22]
why does alkynes are less reactive
than alkanes towards electrophilic
addition reaction?
Ans]Inspite of having two π- bonds ,alkynes are less
reactive than alkenes having one π- bond towards
electrophilic addition reaction because
(1)Carbon atom in alkynes is sp hybridised which is more
electronegative than the sp2 hybridised carbon atom
incase of alkene as a a result , π- electrons are more
tightly held by the C- atoms of alkynes as compared to the
π-electrons of alkene . Thus it is clear that electrons are
easily available for the reaction with electrophilies in case
of alkene.
Q23]
Optically active 2-iodobutane on
treatment with NaI in acetone give a
product which does not show optical
activity. why?
Ans]Optically active 2-iodobutane on
treatment with NaI in acetone
undergoes racemization and hence
the product does not show optical
activity .when 2-iodobutane (I)is
treated with I- ion , it undergoes
Walden inversion SN2 reaction to give
2-iodobutane(II)which is the
enantiomer of (I).
Q4]
Why CHF3 is less reactive than CHCl3
though fluorine is more
electronegative than the chlorine?
Ans] CCl3 by the removal of proton
from CHCl3 is stabilized by resonance
due to presence of d-orbitals in
chlorine while CF3 is not stabilized by
resonance due to absence of dorbitals in fluorine.
Q5]
Haloarenes are insoluble in water
but soluble in benzene. Why?
Ans]Haloarenes are insoluble in
water as it cannot break the Hbonding already In water or it
cannot form H –bonding with water
. It is known that like dissolves like
,haloarenes due to presence of a
large hydrocarbon part are soluble
In hydrocarbon solvents such as
benzene , ether etc.
Q6]
Why does alcohol react with halogen
acids to form haloalkanes while
phenol does not form halobenzene?
Ans] Alcohols react with halogen
acids to form haloalkanes while
phenol does not form halobenzene
because C-O bond in phenols has
some double bond character due to
resonance.
Because of this double bond
character C-O bond cannot be
cleaved by halide ions in the
presence of halogen acids to form
Q7]
Why does dehydration of alcohols is
carried out with conc. Sulphuric acid
and not with conc. HCl or HNO3 ?
Ans]Dehydration of alcohols is carried out with
conc. Sulphuric acid and not with conc. HCl or
HNO3 because this reaction proceeds via the
cabocations . On using HCl, the nucleophile Cl- ion
yield a substituted product to give alkyl chloride
.In case of conc. H2SO4 there is bisulphate ion
which is non nucleophilic hence we cannot get
substituted product. Conc. HNO3 is strong oxidising
agent.
Q8]
Why ether s are purified before
distillation ?
Ans] Ethers are purified before
distillation because of presence of
peroxide in ether . Concentration of
peroxide increases on distillation
which may then explode . It is for
this reason only ethers are purified
by mixing with ferrous sulphate
solution which reduces the hydrogen
peroxide to non explosive alcohols .
Q9]
why does aromatic aldehydes and
ketones are less reactive than
aliphatic aldehydes and ketones?
Ans]Aromatic aldehydes and
ketones are less reactive than
aliphatic aldehydes and ketones
because electron donating effect (+R
effect) of benzene ring increases
electron density on the carbonyl
carbon thereby repelling the
nucleophile.
Q10]
Why urea is basic?
Ans]It is because of oxygen atom in
resonating structure can accept
proton to form a new –OH bond as
it (O- atom)carries negative charge.
The product containing positive
charge is also resonance stabilized .
Q.1 Optically active 2-iodobutane on
treatment with NaI in acetone gives a
product which does not show optical
activity.Explain.
Ans:In the reaction with NaI,C-I bond first cleaves and then
reforms.This leads to the formation of a racemic mixture
which is optically inactive.
CH3
CH3
|
-I
|
+I
H–C–I  H–C 
|
| (NaI)
C2H5
C 2 H5
CH3
CH3
|
|
H–C–I+I–C–H
|
|
C2H5
C2H5
Q.2 Ketones are less reactive towards
nucleophiles than aldehydes.Give
reason.
Ans:Ketones are less reactive than
aldehydes towards nucleophilic
addition reactions because:(i)they have
two electron-donating alkyl groups
which reduce the residual positive
charge on carbonyl carbon,and (i)the
tetrahedral intermediate is more
crowded in case of ketones.
Q.3 Benzoic acid a stronger acid than
ethanoic acid.Explain.
Ans:- Because(i) Benzene ring is
electron withdrawing and facilitates
the release of H+ ion and e-.
(i) the resulting carboxylate anion is
stabilized by resonance.
In ethanoic acid,CH3-group increases
the e- density on coo group and
makes the release of H+ difficult.Also
the resulting carboxylate anion can’t
stabilize by resonance.
Q.4 The presence of benzoquinone
inhibits the free radical
polymerization of a vinyl
derivative.Explain.
Ans:Benzoquinone traps the radical
intermediate to form a non reactive
radical which is highly stabilized by
resonance: because of the lack of
reactivity of this
intermediate,further progress of
the chain reaction is interrupted
and the reaction stops.
Q.5 The basic strength of aliphatic
amines in solution is of the order of
sec>tert>primary.Give reason.
Ans:Basic character of of amines is due
to e- density on N atom.Alkyl group
is an e- releasing group which
increases the e- density on the N
atom.Hence e- density will be the
greatest on N atom in the tertiary
amines.But due to the steric
hidrance, the capture of proton H+ is
obstructed and hence the given
order.
Q.6 Nitro compound have higher
boiling points than hydrocarbons
having proportionally same
molecular mass.Give reason.
Ans:Due to polar nature,the boiling
points of nitro compounds are
usually high in comparison with
hydrocarbons having proportionally
same molecular mass.
Q.7 Phenol on reacting with
bromine in non polar solvent like
CS2,CCl4,CHCl3 at 273 K produce a
mixture of o-bromo phenol p-bromo
phenol.Explain why o-bromo phenol
is formed as minor product.
Ans:o-bromo phenol is formed as minor
product because the transition state
formed in the formation of o-bromo
phenol is destablished due to (i)there
is no attraction between H of OH
group and electrophile Br+(ii) there is
strong repulsion in between OH
group and electrophile Br+ as they
are adjacent to each other.
Q.8 Preparation of ethers by
willumsons’synthesis is not applicable
for tertiary alkyl halides.Give reason.
Ans:This method is not applicable to
tertiary alkyl halides because the
alkoxide ion is powerful nucleophile
or base which cause
dehydrohalogenation of tertiary
halide and form alkene
preferentially.It’s very successful
with alkyl halides and the
mechanism is SN2 type.
Q.9 Aqueous solution of amines is
weakly basic.Explain.
Ans:- R3N + HOH  R3 – N+H + -OH
In the above
reaction -OH ion is stronger base than alkyl amine
hence,it has greater attraction for proton than
amine.Therefore equilibrium shifts to the left side i.e.
rate of backward reaction is more.Therefore aqueous
sol.of amines mainly contains undissociated molecules of
amines. Therefore aqueous sol.of amines is weakly basic.
Q.10 Aromatic amines i.e.aniline is
less basic than ammonia and
aliphatic amines.Give reason.
Ans:- Aromatic amines
i.e.aniline(C6H5NH2) is less basic than
ammonia and aliphatic amines. It is
because phenyl group exerts –I
effect i.e. it withdraws electrons and
electron pair is delocalised due to
resonance.This results in the lower
availability of electrons on nitrogen
for protonation.
(1)NH has a higher proton affinity
than PH . Why?
3
3
Ans. When NH or PH accepts a
proton, an additional N—H or P—H
bond is formed. However, due to
smaller size of N over P, N—H bond
thus formed is much stronger than the
P—H bond. Therefore, NH has high
proton affinity than PH
3
3
3
3
(2)NO(Nitric oxide)is paramagnetic in
the gaseous state but diamagnetic in
the liquid and solid states. Why ?
Ans. NO has an odd no. of
electrons(7+8 =15 electrons)and
hence is paramagnetic in the gaseous
state. But in liquid and solid states, it
exists as a symmetrical or
asymmetrical dimer and hence is
diamagnetic in these states.
(3)Bismuth is a strong oxidising agent
in the pentavalent state. Why ?
Ans . Since the inert pair effect is
very prominent in Bi, therefore, its
+5 oxidation state is much less
stable than its +3 oxidation state. In
other words, Bi in the pentavalent
state can easily accept two
electrons and thus gets reduced to
more stable trivalent Bi.
(4)SF is known but SH is not known
.Why?
6
6
Ans . Fluorine being the strongest
oxidising agent oxidises sulphur to
its maximum oxidation state of +6
and thus forms SF6 . In contrast H2
being weak oxidising agent cannot
oxidise Sto its maximum oxidation
state of +6 and hence does not
form SH6
(5)Sulphur hexafluoride is used as a
gaseous electrical insulator . Why?
Ans . SF6 is a colourless, odourless
and non toxic gas at the room
temperature. It is thermally stable
and chemically inert. Because of its
inertness and high tendency to
suppress internal discharges, it is
used as a gaseous insulator in high
voltage generators and switch
gears.
(6)Chromium is a typical hard metal
while mercury is a liquid. Why?
Ans . Cr has five unpaired d
electrons in the d- subshell. Hence ,
metallic bonds are very strong. In
Hg, all the d- orbitals are fully filled.
Hence, the metallic bonding is very
weak.
(7) Why is separation of lanthanide
elements difficult?
Ans . Due to lanthanide contraction,
the change in the atomic or ionic radii
of these elements is very small.
Hence, their chemical properties are
similar. This makes their separation
difficult.
(8) Transition metal fluorides are
ionic in nature whereas bromides
and chlorides are usually covalent in
nature.why?
Ans . As electronegativity of
halogens decreases in the order F >
Cl > Br, the ionic character of
transition metal halides decrease in
the order
M—F > M—Cl> M—
Br. Hence, fluorides are ionic in ionic
whereas chlorides and bromides are
covalent.
(9) Chemistry of all the lanthanoids is
quite similar. Why?
Ans . The change in the size of the
lanthanoid contraction is very small
as we proceed from La(z = 57) to
Lu(Z=71). Hence, their chemical
properties are similar. Moreover,
their valence shell configuration
remains same because the electrons
are added into the inner 4f-subshell.
Hence, they show similar chemical
properties.
(10)Actinoids exhibit a larger no. of
oxidation states than the
corresponding lanthanoids?
Ans . Actinoids show a large no. of oxidation states because
the energy gap between 5f,6d and 7s subshells is very small
and hence all the electrons present in these subshells can
participate in bonding whereas lanthanoids show a limited
number of oxidation states because the energy gap
between 4f and 5d subshells is large and all the electrons in
these subshells cannot participate in bonding.
Q- Why are Alkanes hydrophobic?
Ans -Alkanes are non polar.
They are insoluble in water because
they lack polar groups that can form
hydrogen bond or participate in
dipole- dipole interactions with water
molecules
Hence alkanes are insoluble in water.
Why do Alkyl halides have higher
boiling points than alkanes?
Ans- Alkyl halides have dipoledipole interactions along with their
van der Waals forces.
So, the attractive force in alkyl
halides are greater than that in
alkanes. Hence they have a higher
boiling point than alkane
Does Nitrous acid react with Methyl
amine?
If yes, what does it form?
Why is the reaction different with
other alkyl amines?
If the alkyl group in alkyl amine is
Methyl, then on reacting with nitrous
acid, it forms a functional group of
alcohols (ether) because as it is very
small, it prefers to split and form
dimethyl ether, unlike other (larger)
alkyl groups which forms alcohols.
Aluminum chloride and Acetic
acid both form dimers, but nature
of both of the dimers are
different. Explain.
In Aluminium chloride,there is back bonding
of chlorine due to an empty orbital of
aluminnum.
In Acetic acid,It bonds with another molecule
by hydrogen bonding.
Write the order of basicity of
primary, secondary and tertiary
alkyl amines.
The order of basicity in alkyl amines is
3º>2º>1º>Ammonia
However, in Aqueous medium it is
different
2º>1º>3º>Ammonia
This is due to steric hindrance.
Why is hydration of alkenes by
oximercuration demercuration
preferred than addition of water in
presence of an acid?
How are both the methods
different?
In oxymercuration demercuration,
there are no side products since there
are no carbocations formed, hence it is
more preferred as it gives a single
product.
Both methods follow markownikoff’s
rule but in
oxymercuration demercuration ,theres
is no rearrangement as no
carbocations are formed.
In Williamson’s Synthesis, the
reaction of sodium alkoxide with a
tertiary alkyl halide does not form
an ether. Why?
Then how can a tertiary group
be reacted so as to form an ether?
Alkoxides are nucleophiles as well as
bases, hence
When there is 3º carbon, elimination
takes over. Hence an alkene is formed.
We can make the 3º carbon as the alkyl
group in the sodium alkoxide ion to
form an ether with an alkyl halide.
Which is more acidic,
Hydroxy group attached to a alkyl
group or an aromatic ring?
Why?
Hydroxy group attached to the
aromatic ring is more acidic because
acidity depends on the extent with
which the oxygen atom remains
stable after it loses hydrogen.
Since R- group are electron releasing
groups, the hydroxy group attached
alkyl groups are less acidic.
1. Nitrogen exists as diatomic
molecule and phosphorus exists as
tetraatomic molecule P4. Explain.
The size of nitrogen atom is quite
small. As a result, two nitrogen atoms
can be linked to each other by three
covalent bonds in order to complete
the octets of both the nitrogen atoms.
However, phosphorus being large in
size has less tendency to form three
bonds. Therefore, P atom completes its
octet by sharing its valence electrons
with three other P atoms. As a result it
2. Though nitrogen exhibits +5
oxidation state, it does not form
pentahalides. Give reason.
Nitrogen belongs to second period and
has only s and p-orbitals. It does not
have d-orbitals in its valence shell and
therefore, it cannot extend its octet.
That is why nitrogen does not form
pentahalides.
3. Why is dinitrogen(N2) less
reactive at room temperature?
In molecular nitrogen, there is a triple
bond between two nitrogen atoms and
it is non-polar in character. Due to the
prescence of a triple bond, it has very
high bond dissociation energy and
therefore it does not react with other
elements under normal conditions and
its very unreactive. However, it may
react at higher temperature.
4. Phosphine has lower boiling
point than ammonia. Give reason.
Ammonia exists as associated molecule
due to its tendency to form hydrogen
bonding. Therefore, it has high boiling
point unlike ammonia, phosphine
molecules are nit associated through
hydrogen bonding in liquid state. This
is because of low electronegativity of P
than N. As a result, the boiling point of
phosphine is lower than that of
ammonia.
5. Unlike phosphorus, nitrogen
shows little tendency for
catenation.
Nitrogen has little tendency for catenation because
N-N single bond is weak. This is because nitrogen has
small size and the lone pairs on two nitrogen atoms
repel each other. On the other hand, phosphorus is
comparatively large in size so that lone pairs on P
atoms do not repel to the same extent. As a result PP bond is stronger than N-N bond. Therefore, P has
a tendency for catenation because of high bond
enthalpy of P-P bond.
6. Why does nitrogen dioxide
dimerise? Explain.
Nitrogen dioxide contains odd number
of valence electrons. It behaves as a
typical molecule. In the liquid and solid
state, it dimerises to form stable N2O4
molecule, with even number of
electrons. Therefore, nitrogen dioxide
is paramagnetic, while N2O4 is
diamagnetic in which two unpaired
electrons get paired.
7. Why does ammonia act as lewis
base?
Nitrogen atom in ammonia has one
lone pair of electrons which is
availaible for donation. Therefore, it
acts as a lewis base.
8. Why does PCl3 fume in nature?
PCl3 gets hydrolysed in the
prescence of moisture and gives
fumes of HCl.
9. All the five bonds in PCl5 are not
equivalent. Justify.
PCl5 has trigonal bypyradimal structure
in which there are three P-Cl equitorial
bonds and two P-Cl axial bonds. The
two axial bonds are being repelled by
two bond pairs at right angle while the
three equitorial bonds are being
repelled by two bond pairs at right
angle. Therefore, axial bonds are
repelled by two bond pairs than
equitorial bonds and hence are larger
10. PCl5 is known but PI5 is not
known? Why?
Due to small size of Cl atom , five Cl
atoms can be accomodated around P
atom. But I is of large size and
therefore fine I atoms cannot be
accomodated around P atom. As a
result P-I bonds are weak and prefer to
form PI3 rather than PI5.
Why Para-dichorobenzene
has a higher melting point
than ortho
dichlorobenzene?
Para-dicholorobenzene is more
symmetrical and fits better in the
crystal lattice of the solid form than
the ortho dicholro benzene
p-methoxybenzyl bromide
reacts faster than p-nitrobenzyl
bromide with ethanol to form
an ether product.?
CH3O-group has a strong electron
donating effect (+R effect) and
increases the e- density around Br
making it easier for the nucleophile to
attack. Why NO2 group has a strong –R
effect,therefor delocalization of +ve
charge is more difficult.
The dipole moment of
chlorobenzene is lower than
that of cyclohexyl chloride?
In chlorobenzene, C of C-Cl bond is sp2
hybridized while in cyclohexyl chloride
has more s-character and is more
electronegative than sp3C,so C-Cl bond in
cyclohexyl choride.Hence,dipole moment
of chlorobenzene is lower than that of
cyclohexyl chloride .
Chloroform is stored in dark
colored bottles.
Chloroform in the presence of air gives a
poisonous phosgene gas. The reaction is
catalysed by light. To slow down this
reaction, we store the CHCl3 in dark
coloured bottles.
Why ethane-1, 2-diol has a
higher boiling point than
ethanol?
Ethane-1, 2-diol contains two OH groups,
therefore the extent of intermolecular
hydrogen bonding is more. Ethane-1,2diol is more associated than ethanol,
hence ethane-1,2-diol has a higher B.P
than ethanol.
What is denatured alcohol and
why is it dangerous to drink?
Denatured alcohol is alcohol made unfit
for drinking by addition of small
quantities of benzene, toxic methanol,
copper sulphate and pyridine.
Which is more acidic and why?
p-chlorophenol or p-nitrophenol
P-nitrophenol is more acidic than pchlorophenol.NO2 group is strongly
electron withdrawing group than Cl due
to the presence of the +ve charge on N
attached directly to the benzene ring.
Do ethers have dipole
moments?
Yes, they are weakly polar. Ether have a
bent structure with a C-O-C bond angle of
-112 degree and the two C-O bond dipole
moments do not cancel.
Why is carboxylic acid a stronger
acid than alcohol?
This is because the conjugate base of
carboxylic acid is more stable than
the conjugate base of alcohol via
resonance
Q.1- Haloarenes are insoluble in water but
are soluble in benzene. Explain.
Ans – Haloarenes are insoluble in water
because these cannot form hydrogen
bonds with water molecules. However,
these are soluble in benzene in
accordance with the general principle
of solubility, i.e., like dissolves like.
Haloarenes are organic compounds
having a large hydrocarbon part
(benzene ring) and are soluble in
hydrocarbon solvents like benzene.
Q.2- The p-isomer of dichloro
benzene has higher melting
point then o- and m-isomer.
Why?
Ans –The melting point of para isomer is
quite higher than that of ortho or meta
isomers. This is due to the fact that it
has symmetrical structure and
therefore, its molecules can easily pack
closely in crystal lattice. As a result
intermolecular forces of attraction are
stronger and therefore, greater energy is
required to break its lattice and it melts
at higher temperature.
Q.3- Iodoform gives a precipitate
with silver nitrate on heating
while choroform does not.
Ans – Carbon-iodine bond is quite weak as
compared to carbon-chorine bond.
Therefore, when Iodoform is heated
with AgNO3 solution, C-I bond gets
cleaved easily and iodide ions react with
AgNO3 solution to give precipitate of
AgI. On the other hand, C-Cl bond does
not get cleaved.
Q.4- A small amount of ethyl
alcohol is usually added to
chloroform bottles. Why?
Ans –Alcohol retards the oxidation of
chloroform to phosgene (any
formed) to harmless ethyl
carbonate.
2C2H5OH + COCl2
(C2H5)2 CO3 +2HCL
Q.5- Organic halogen compounds
used in industry as solvents are
chlorides rather than bromides
and iodides. Explain
Ans- Organic alkyl chlorides are
used in industry as solvent
because chlorides are more
volatile than bromides and
iodides.
Q. 6- Ethyl chlorides is a gas,
whereas ethyl iodide is liquid at
room temperature. Explain
Ans – Ethyl iodide has large
molecular mass and therefore has
large van der Waal’s forces. Thus it
is liquid at room temperature.
Q.7- The use of chloroform as an
aesthetic is decreasing. Why?
Ans – Because in cases, CHCl3 causes
cardiac and respiratory problems.
Therefore, its use as an aesthetic is
decreasing.
• Q.8-Allyl chloride is more than npropyl chloride towards
nucleophilic substitution
reaction. explain why?
Ans- Allyl chloride is more than npropyl chloride towards
nucleophilic substitution reaction.
This is because of greater
stabilization of allylic carbocation
intermediate formed by resonance.
CH2=CH-CH2
CH2 -CH=CH2
Q.9- 1-chloroethane has less
boiling point than 2-methyl-2chlorobutane. Why ?
Ans – 2-methyl-2-chlorobutane has
higher boiling point than 1chlorobutane because with increase
in size of alkyl group, boiling point
increases.
Q.10- Sodium metal can be used
for drying diethyl ether but not
ethanol. Why ?
Ans –sodium metal reacts with
ethanol to form sodium ethoxide
but does not reacts with ether.
Q. 1 – Nitric oxide becomes brown
when released in air.
Ans –When nitric oxide,
NO is release in air, it
becomes brown due to
the formation of NO2
(nitrogen dioxide),
which is brown gas.
2NO(g)+O2(g)
2NO2(g)
Q.2- Concentrated
nitric acid turns
yellow on exposure to
sunlight. Why?
Ans – On exposure to sunlight,
nitric acid decompose into
NO2,O2, and H2O. The presence
of NO2 in the partially
decomposed nitric acid gives it
yellow colour.
4HNO3(l)
4NO2(g)+O2(g)+2H2O(l)
Q.3-PCl5 is known but PI5
is not known. Why ?
Q.- Due to small size of Cl atoms
can be accommodated around P
atoms. But I is of larger size and
therefore, 5 I atoms cannot be
accommodated around P atom.
As a result, P-I bonds are weak
and prefer to form PI3 rather
than PI5.
Q.4 –NCl3 gets readily hydrolysed while
NF3 does not. Why?
Ans.- In NCl3, Cl has vacant d –
orbitals to accept lone pair of
electrons present on oxygen atom
of water molecule.
Q.5- Noble gas have low boiling points.
Explain ?
Ans.- Noble gases are monatomic gases
and held together by weak van der
Waal’s forces (dispersion forces).
Therefore, they are liquefied at very
low temperatures. Hence they have
low boiling points.
Q.6- Out of noble gases,
only xenon is known to
form chemical
compounds.
Ans. – Except randon, which is
radioactive, xenon has lowest
ionisation enthalpy among
noble gases and hence it
readily forms chemical
compounds particularly, with
O2 and F2
Q.7- Why is KMnO4
solution used to clean
surgical instruments in
hospital.
Ans .KMnO4 solution used to clean surgical
instruments in hospital because of the
germicidal action of KMnO4.
Q.8- In moist air, copper corrodes to
produce a green layer on its surface.
Explain.
Ans.-In the presence of moist air, a thin film of green basic
copper carbonate is formed on its surface and therefore, it
corrodes.
2Cu+O2 +H2O +CO2
CuCO3.Cu(OH)2
Basic copper carbonate
(Green)
Q.9- CrO3 is an acid
hydride. Explain.
Ans.- CrO3 readily dissolves in water to
give rise chromic acid, which acts as
strong acid. Therefore, CrO3 is an acid
anhydride
CrO3+ H2O
H2CrO4
Chromic acid
Q.10- Why do Zr and Hf exhibit similar
properties?
Ans –Due to lanthanoid contraction,
Hf and Zr have almost similar size
and therefore, their properties are
similar.
Q- Haloarenes are insoluble in water but
are soluble in benzene. Explain.
ANS-Haloarenes are insoluble in water
because these cannot form hydrogen
bonds with water molecules. However,
these are soluble in benzene in
accordance with the general principal
of solubility i.e. like dissolves like.
Haloarenes are organic compounds
having a large hydrocarbon part and
are soluble in hydrocarbon solvents like
benzene.
Q- The p-isomer of dichlorobenzene has
higher melting point than o- and misomer. Why?
• ANS- The melting point of para isomer is quite
higher than that of ortho or meta
isomers. This is due to the fact that it has
symmetrical structure and hence its molecules
can easily pack closely in crystal lattice. As a
result intermolecular forces of attraction are
stronger and hence greater energy is required
to break its lattice and it melts at higher
temperature.
Q- Iodoform gives a precipitate with
silver nitrate on heating while chloroform
does not. Explain why?
• ANS- Carbon-iodine bond is quite weak
[213.4kJ/mol] as compared to carbonchlorine bond [326.4kJ/mol]. Hence when
iodoform is heated with silver nitrate
soln,C-I bond gets cleaved easily and iodide
ions react with silver nitrate soln to give
ppt of AgI . On the other hand, C-Cl bond
doesn’t get cleaved .
Q- Why do alcohols have higher boiling
points than haloalkanes of the same
molecular mass?
• ANS- The b.p of alcohols are higher than
the corresponding haloalkanes of the same
molecular mass mainly due to strong
intermolecular H bonding between alcohol
molecules. Because of H bonding in alcohols
, energy has to be supplied to overcome
the force of attraction and consecutively
b.p are high. No such H bonding exists in
haloalkanes .
Q- Ethers possess a dipole moment even if
the alkyl radicals in the molecule are
identical. Explain.
• ANS- Ethers have angular structure similar
to water, in which oxygen involves
•
Sp3
hybridisation. Oxygen is surrounded
sp
by two O-R bonds and
2 lone pairs .due to
angular structure ethers have dipole moment
even if the the 2 alkyl groups are identical
because 2 C-O moments do not cancel each
other.
3
Q- Aldehydes and ketones have lower
boiling points than corresponding alcohols
and acids. Explain.
• ANS- Aldehydes and ketones are polar
compounds having sufficient intermolecular
dipole-dipole interactions between opposites
ends of C=O dipoles. However,these dipoledipole interactions are weaker than the
intermolecular H bonding present in alcohols
and acids. Hence b.p of aldehydes and
ketones are lower than alcohols and
carboxylic acids.
Q- p-methoxyaniline is a stronger base
than aniline but p-nitroaniline is a weaker
base than aniline. Explain.
• ANS- Methoxy group is electron releasing
group and increases the electron density on
N atom. Hence it has greater electron
donating tendency than aniline and thus is a
stronger base than it. On the other hand
nitro group is electron withdrawing group
and hence decreases the electron density
on N atom. As a result p- nitroaniline is a
weaker base than aniline.
Q- Although trimethyle amine and npropylamine have the same molecular mass
, the former boils at lower temperature
[276K] and the latter [322K]. why?
• ANS- n-propylamine has 2 H atoms on the
N atom and hence forms intermolecular H
bonding . Hence its b.p is high . Whereas,
trimethylamine does not undergo H bonding
and hence its b.p is low.
Q- Tertiary amines
acylation. Explain why?
do
not
undergo
• ANS- Amines containing replaceable H atom
react with acid chloride or acid anhydride
to form substituted amides. This reaction
is called acylation reaction. In case of
tertiary amines there is no replaceable H
atom and hence , these do not react with
acetyl chloride or acetic anhydride and do
not undergo acylation .
Q- Electrophilic substitution in case of
aromatic amines takes place more readily
than benzene. Explain
• ANS- Amine group in aromatic amines
strongly activates the aromatic ring through
delocalisation of the lone pair of electrons
on N atom over the aromatic ring.
However, no such delocalisation occurs in
case of benzene.
Haloarenes are insoluble in water
but soluble in benzene. Why?
Haloarenes are insoluble in water as
it can’t break H bonding already
existing in water. Like dissolves like
therefore haloarenes having large
hydrocarbon part are soluble in
similar solvents like benzene.
Acid catalyzed dehydration of nbutanol is slower than t-butanol.
Why?
The dehydration of t-butanol involves
the formation of stable tertiary
carbocation which is more stable than
the primary carbocation formed in nbutanol thus having more tendency
to dehydrate.
O-Nitrophenol is more volatile than pnitrophenol. Why?
Intermolecular hydrogen bonding
present in p-nitrophenol helps
molecules to associate hence
increasing the boiling point. In onitrophenol, intramolecular H
bonding doesn't help in association.
Phenol undergoes Kolbe’s reaction
but ethanol doesn't. Why?
Phenol is acidic in nature due to
resonance stabilization of phenoxide
ion. There is no such effect in ethanol.
Phenol is less acidic than p-nitro
phenol. Why?
This is due to resonance stabilization
of p-nitrophenolate ion and also
strong –I effect of nitro group.
Ethers behave as bases in presence of
mineral acids. Why?
Due to presence of lone pair of
electrons on oxygen atom, ethers
behave as lewis base and form stable
oxonium salts with strong inorganic
acids at low temperature.
Grignard reagents are prepared in
ethers and not other solvents. Why?
Grignard reagents are very sensitive
to presence of H+. As ethers don’t
contain H+ they are used as solvent
for preparation of Grignard reagents.
Lower aldehydes and ketones are
soluble in water but solubility
decreases as the molecular weight
increases. Why?
As the mol. wt. increases the
hydrocarbon part increases which
reduces the extent of H-bonding thus
reducing the solubility.
Alpha hydrogen atoms in aldehydes
and ketones are acidic. Why?
The carbanion formed after loss of
Alpha hydrogen is stabilized by
resonance.
Benzoic acid doesn’t give Friedel
Craft’s reaction. Why?
The carboxylic group is electron
withdrawing and hence deactivates
the benzene ring towards
electrophilic attack. Hence benzene
ring doesn’t give Friedel Craft’s
Reaction.
Q 1. Why is thionyl chloride preferred over PCl5 in
nucleophilic substitution reaction to convert alcohol to
alkyl halide ?
Ans: It is because all by-products are gases
and escape easily and pure alkyl halide is
obtained.
Q 2. Explain why alcohols are comparatively
more soluble in water than the corresponding
hydrocarbons .
Ans: Alcohols are more soluble in water because they
can form H-bonds with water whereas
hydrocarbons cannot form H-bonds as they are nonpolar.
Q 3. Chloroform contains chlorine but gives no reaction
with silver nitrate solution. Why?
Ans: Chloroform contains but it is bonded to carbon by
covalent bond and therefore ,it is not in ionic form. Hence
,it does not give any reaction with silver nitrate solution.
Q 4. Unlike phenols, alcohols are easily
protonated. Give reason.
Ans: In alcohols ,the electron releasing inductive effect
(+I effect) of the alkyl group attached to the carbon
having the –OH group increases the electron density on
the oxygen atom. Therefore, alcohols are easily
protonated. On the other hand, in case of phenol the
oxygen atom acquires a partial positive charge due to
resonance. Hence, it is not protonated.
Q 5. Why are ethers relatively inert compounds?
Ans: Ethers are inert compounds because the functional
group of ethers(-O-) does not contain any active site.
Therefore ,under ordinary conditions, they are stable to
bases, dilute acids and other reducing agents.
Q 6. Ethers posses a dipole moment even if the alkyl
radicals in the molecule are identical. Explain.
Ans: Ethers have angular structure similar to water, in
which oxygen involves sp3 hybridization . Oxygen is
surrounded by two O-R bonds and two lone pairs. Due to
angular structure, ethers have dipole moment even if the
alkyl groups are identical because two C-O moments do
not cancel each other.
Q 7. Aldehydes and ketones have lower boiling points
than corresponding alcohols and acids. Explain.
Ans: Aldehydes and ketones are polar compounds having
sufficient intermolecular dipole-dipole interactions
between opposite ends of >C=O dipoles. However ,these
dipole-dipole interactions are weaker than the
intermolecular hydrogen bonds present in alcohols and
carboxylic acids. Therefore, B.P. of aldehydes and ketones
is lower than alcohols and acids.
Q 8. Highly branched carboxylic acids are less acidic
than unbranched acids. Why?
Ans: The carboxylate ion ,(RCOO-) of branched
chain acids is shielded from solvent molecules and
therefore cannot be stabilized by solvation as effectively
as the carboxylate ion of unbranched acids.
Q 9. Electrophilic substitution in case of aromatic amines
takes place more readily than benzene. Explain.
Ans: NH2 group in aromatic amines strongly activates the
aromatic ring through delocalisation of the lone pair of
electrons an N-atom over the aromatic ring. However, no
such delocalisation occurs in case of benzene.
Q 10. Sulphanilic acid is soluble in dilute NaOH but not in
dilute HCl. Explain.
Ans: Sulphanilic acid exists as a zwitter ion. In the
presence of dilute NaOH,the weakly acidic NH3(+) group
transfers its H(+) to OH(-) to form a solute p-NH3+ C6H4
SO3H. Hence, it does not dissolve in dilute HCl.
Ques-1)
Unlike phenols, alcohols
are easily protonated.
In phenols, the lone pairs of electrons on
the oxygen atom are delocalized over the
benzene ring due to resonance & hence
are not easily available for protonation.In
contrast in alcohols,the lone pairs of eon the oxygen atom are localized due to
absence of resonance & hence are easily
available for protonation.
Ques-2)
How do you account for the
fact that unlike phenol, 2,4dinitrophenol & 2,4,6trinitrophenol are soluble in
aq. sodium carbonate
solution?
Due to the electron-withdrawing nature of
-NO2 groups, both 2,4-dinitrophenol &
2,4,6-trinitrophenol are more acidic than
carbonic acid & hence dissolve in aq.
Na2 CO3 solution to form the corresponding
sodium salts with the evolution of CO2.
Ques-3)
Alcohols react with halogen acids or
phosphorous halides to form haloalkanes
but phenol does not form halobenzene.
Explain.
The C-O bond in phenols has some double
bond character due to resonance & hence
cannot be easily cleaved by X- ions in
presence of halogen acids or phosphorous
halides to form halobenzenes. In contrast,
the C-O bond in alcohols is a pure single
bond & hence can be easily cleaved by Xions in presence of halogen acids or
phosphorous halides to form haloalkanes.
Ques-4)
Explain why dehydration of alcohols to
form alkenes is always carried out with
conc.H2SO4 & not with conc.HCl.
Dehydration of alcohols to form
alkenes occurs through carbocation
intermediates.If HCl is used, then
chloride(Cl-)ion being a good
nucleophile bring about substitution
reaction to give an alkyl chloride.If
H2SO4 is used, then the bisulphate
ion being non-nucleophilic cannot
bring about substitution reac.Instead
carbocation losesa proton to form an
alkene.
Ques-5)
Di-tert-butyl ether cannot be made
by Williamson’s synthesis.Explain
why?
To prepare di-tert-butyl ether by
Williamson’s synthesis,we need
sodium tert-butoxide& tert-butyl
bromide.Since tert-butyl bromide
being a tertiary alkyl halide prefers
to undergo elimination rather than
substitution,therefore the product
obtained is isobutylene rather than
di-tert-butyl ether.
Ques-6)
Explain why ethers are cleaved
only by acids & not by bases.
The C-O-C bond in ethers like the
C-OH bond in alcohols is quite strong.In order to
weaken it,the oxygen atom must be protonated.A
subsequent nucleophilic attack by a
strong nucleophilie such as Br- or Iion on the less hindered carbon atom of the C-O-C
bond brings about the cleavage of ether to form an
alcohol &an alkyl halide.
On the other hand,bases cannot
weaken the C-O-C bond because
ehers themslves being Lewis bases
are not attacked by strong bases
such as OH- or H- ion.In other
words,bases cannot cleave ethers.
Ques-7)
Di-tert butyl ether is rapidly cleaved
even by hydrogen chloride at room
temp to give tert-butyl chloride.
Explain.
The di-tert-butyl oxonium ion(I)first
formed by protonation of di-tert-butyl
ether is highly crowded &hence
cannot be attacked by the chloride
ion.Therfore,it does not undergo cleavage by SN2
mechanism.Instead
it prefers to undergo cleavage by
SN1 mechanism since tert-butyl
carbocation is very stable.
Ques-8)
Although aldehydes are easily
oxidisable yet propanal can
conveniently be prepared by the
oxidation of propanal by acidic
potassium dichromate.
Aldehydes can be obtained in quantitative
yield by the oxidation of primary alcohols
provided these are removed from the reacn
mixture assoon as they are formed to
prevent their further oxidation to carboxylic
acids.Since aldehydes having B.P less than
373 K can be easily removed by distillation
therefore,propanal can be easily prepared
from propanol-1 by distilling it from the
alcohol-acid dichromate solution.
Ques-9)
Fluorine is more e-negative than Cl
even then, p-flurobenzoic acid is a
weaker acid than p-chlorobenzoic
acid.Explain.
Since halogen are more e-negative than C
& also posses lone pairs of e-,therefore,
they exert both –I & +R-effects.Now in F,the
lone pairs of e- are present in 2p-orbitals but
in Cl,they are presents in 3p-orbitals.Since
2p-orbitals of F & C are of almost equal
size,therefore the +R-effect is more in pflurobenzoic acid than in p-chlorobenzoic
acid.Thus in p-furobenzoic acid, +R-effect
outweighs the –I-effect but is p-chlorobenzoic
acid,it is the –I-ffect which outweighs the +Reffect.Thus,p-flurobenzoic
acid is a weaker acid than
p-chlorobenzoic acid.
Vinyl Chloride is unreactive in
nucleophilic substitution reactions.
Why ?
Neo-pentyl bromide undergoes
nucleophilic substitution reaction
very slowly. Why ?
Vinyl chloride is unreactive in
nucleophilic substitution reactions
because of double bond character
between carbon and chlorine.
This bond is difficult to break.
Neo-Pentyl bromide is primary
halide and it forms primary
carbocation. This is less stable,
therefore, it undergoes nucleophilic
substitution reaction slowly.
3-bromocyclohexene is more reactive
than 4-bromocyclohexene in
hydrolysis with aqueous NaOH.Why ?
Tert-butyl chloride reacts with
aqueous NaOH by Sn1 mechanism
while n-butyl chloride reacts by Sn2
mechanism. Why ?
3-Bromocyclohexene forms allyl
carbocation.This is more stable than
carbocation formed by 4-Bromocyclohexene.
Therefore, 3-Bromocyclohexene undergo
hydrorlysis faster in aqueous NaOH.
Tertiary butyl chloride forms tertiary
carbocation which is stabilized by +I
effect (positive inductive effect). It
follows Sn1 mechanism whereas nbutyl chloride forms transition state
because it is primary halide. Rate of
reaction depends on concentration
of both n-butyl chloride and NaOH,
it undergoes Sn2 mechanism.
The nucleophilic substitution of
primary alkyl chlorides with sodium
acetate is catalysed by sodium
iodide. Why ?
p-Methoxybenzyl bromide reacts
faster than p-nitrobenzyl bromide
with ethanol to form an ether
product. Explain why ?
Primary alkyl chloride reacts with
sodium iodide to form primary alkyl
iodide. This alkyl iodide is more
reactive than alkyl halide with
sodium acetate. This is the reason
why the nucleophilic substitution of
primary alkyl chloride with sodium
acetate is catalysed by sodium
iodide.
Methoxy group is electron
releasing, therefore it stabilises
carbocation formed by pmethoxybenzyl bromide whereas
nitro group being electron
withdrawing group destabilises
carbocation formed by pnitrobenzyl bromide.
Explain why the dipole moment of
chlorobenzene is lower than that of
cyclohexyl chloride.
Explain why alkyl halides, though
polar, are immiscible with water.
Chlorobenzene is stabilised by
resonance and there is +ve charge on
Cl in 3 out of 5 resonating structures,
hence, it has lower dipole moment
than cyclohexyl chloride in which
there is no such +ve charge.
Alkyl halides, although polar, cannot
form H-bonds with water and cannot
break H-bonds between water
molecules. Hence, they are insoluble
in water.
Grignard’s Reagent should be
prepared under anhydrous
conditions. Why?
Preparation of ethers by acid
dehydration of secondary or
tertiary alcohols is not a suitable
method. Give reason.
Grignard's reagents react with water to
form alkanes. They are thus prepared
under anhydrous conditions.
It is because dehydration of
secondary and tertiary alcohols will
take place faster leading to formation
of alkenes and will not form ethers.