Q2. Explain why alkyl halides,though polar,are immiscible with water?

Q1. Haloalkanes undergo nucleophilic substitution whereas haloarenes undergo electrophilic substitution.WHY?

Ans 1. Haloalkanes are more polar than Haloalkanes are more polar than haloarenes.Consequently the carbon atom carrying the haloarenes.Consequently the carbon atom carrying the halogen in haloalkane is more electron deficient than that halogen in haloalkane is more electron deficient than that in haloarenes.As the result halalkane undergo in haloarenes.As the result halalkane undergo nucleophilic substitution more readily than haloarenes.nucleophilic substitution more readily than haloarenes.

In contrast haloarenes contain a benzene ring.since the In contrast haloarenes contain a benzene ring.since the typical reaction of benzene are electrophilic typical reaction of benzene are electrophilic substitution,therefore haloarenes undergo electrophilic substitution,therefore haloarenes undergo electrophilic substitutionsubstitution.

Q2. Explain why alkyl halides,though polar,are immiscible with water?

Ans2. Alkyl halide are polar molecules, therefore,their Alkyl halide are polar molecules, therefore,their molecules are held together by dipole-dipole molecules are held together by dipole-dipole attraction.The molecules of water are held together by H attraction.The molecules of water are held together by H bonds.Since the new force of attraction between water bonds.Since the new force of attraction between water and alkyl halide molecules are weaker than the force of and alkyl halide molecules are weaker than the force of attraction already existing between alkyl halide-alkyl attraction already existing between alkyl halide-alkyl halide molecule and water-water molecules.Thus alkyl halide molecule and water-water molecules.Thus alkyl halide are immiscible with water.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 Ans 3. Free radical substitution occurs at the METHYL group giving occurs at the METHYL group giving first benzyl chloride, then benzal first benzyl chloride, then benzal dichloride and finally dichloride and finally benzotrichloride.benzotrichloride.

Q4. Which is stronger acid phenol or cresol?

Ans 4. Due to the I+ effect of CHDue to the I+ effect of CH33 grp grp electron –density in the O-H bond electron –density in the O-H bond increases.Thus it becomes difficult increases.Thus it becomes difficult to break the O-H bond as compared to break the O-H bond as compared to that of the phenol & hence cresol to that of the phenol & hence cresol is more acidic than phenol.is more acidic than phenol.

Q5. Why gridnard reagent soluble in ether but not in benzene?

Ans 5. Gridnard reagent form Gridnard reagent form coordination complexes with ether coordination complexes with ether but not with benzene since the but not with benzene since the ether has lone pairs of electron but ether has lone pairs of electron but the benzene does not.the benzene does not.

Q6. What makes ethanoic acid more stronger than ethanol.

Ans 6. Ethanoate ion obtained by Ethanoate ion obtained by loss of proton from ethanoic acid is loss of proton from ethanoic acid is stabilized by resonance but ethoxide stabilized by resonance but ethoxide ion obtained by loss of proton from ion obtained by loss of proton from ethanol is not.This makes ethanoic ethanol is not.This makes ethanoic acid more stronger than ethanol.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 Due to the strong electron donating effect (+R-effect) of NHdonating effect (+R-effect) of NH22 grp, the electron density on grp, the electron density on benzene ring increases. As a result, benzene ring increases. As a result, aniline is easily oxidised on standing aniline is easily oxidised on standing in air for long time to form coloured in air for long time to form coloured products.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 Nitro compounds have high dipole moments and thus have dipole moments and thus have strong dipole-dipole strong dipole-dipole interaction.Therefore ,their boiling interaction.Therefore ,their boiling points are much higher as compared points are much higher as compared to hydrocarbons or other to hydrocarbons or other compounds of same molecular mass.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 Due to the electron donating resonance effect of NH2 grp the carbon nitrogen bond in the effect of NH2 grp the carbon nitrogen bond in the aromatic amines has some double bond aromatic amines has some double bond character.character.

In contrast in the aliphatic amines the In contrast in the aliphatic amines the carbon –nitrogen bond has only single bond carbon –nitrogen bond has only single bond character therefore carbon-nitrogen bond length character therefore carbon-nitrogen bond length in aromatic amines is shorter than in aliphatic in aromatic amines is shorter than in aliphatic amines. amines.

Q10. Why do amines act as nucleophiles?

Ans 10. Due to the presence of lone Due to the presence of lone pair of electron on the N-pair of electron on the N-atom,amines can easily donate this atom,amines can easily donate this lone pair to the carbon species and lone pair to the carbon species and hence act as nucleophiles.hence act as nucleophiles.

Q.11) p-Dichlorobenzene has highmelting point & lower solubility than ortho and meta isomers. Discuss.

ANS: The p-isomers being more 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+ + Cl-

CH2=CH-CH2-OH CH2+-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. Explainwhy 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 H-bonds 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.ORWhy 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 electron-donating 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 d- orbitals in fluorine.

Q5]Haloarenes are insoluble in water but soluble in benzene. Why?

Ans]Haloarenes are insoluble in water as it cannot break the H-bonding 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 halobenzene.

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 C2H5

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)NH3 has a higher proton affinity than PH3 . Why?

Ans. When NH3 or PH3 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, NH3 has high proton affinity than PH3

(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)SF6 is known but SH6 is not known .Why?

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 moleculesHence alkanes are insoluble in water.

Why do Alkyl halides have higher boiling points than alkanes?

Ans- Alkyl halides have dipole-dipole 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>AmmoniaHowever, in Aqueous medium it is different2º>1º>3º>AmmoniaThis 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, henceWhen 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 exists as P4 molecule.

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 P-P 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 equitorial bonds.

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-1,2-diol 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 p-chlorophenol.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 n- propyl chloride towards nucleophilic substitution reaction. explain why?

Ans- Allyl chloride is more than n- propyl 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-2-chlorobutane. Why ?

Ans – 2-methyl-2-chlorobutane has higher boiling point than 1-chlorobutane 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.

QQ-- Haloarenes are insoluble in water but are soluble in benzene. Explain.

ANSANS-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- Q- The p-isomer of dichlorobenzene has higher melting point than o- and m-isomer. Why?

• ANS-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- Q- Iodoform gives a precipitate with silver nitrate on heating while chloroform does not. Explain why?

• ANS-ANS- Carbon-iodine bond is quite weak [213.4kJ/mol] as compared to carbon- chlorine 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- Q- Why do alcohols have higher boiling points than haloalkanes of the same molecular mass?

• ANS- 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-Q- Ethers possess a dipole moment even if the alkyl radicals in the molecule are identical. Explain.

• ANS- ANS- Ethers have angular structure similar to water, in which oxygen involves

• SpSp33 hybridisation. Oxygen is surrounded 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.

3sp

Q- Q- Aldehydes and ketones have lower boiling points than corresponding alcohols and acids. Explain.

• ANS- ANS- Aldehydes and ketones are polar compounds having sufficient intermolecular dipole-dipole interactions between opposites ends of C=O dipoles. However,these dipole-dipole 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-Q- p-methoxyaniline is a stronger base than aniline but p-nitroaniline is a weaker base than aniline. Explain.

• ANS- 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- Q- Although trimethyle amine and n-propylamine have the same molecular mass , the former boils at lower temperature [276K] and the latter [322K]. why?

• ANS- 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- Q- Tertiary amines do not undergo acylation. Explain why?

• ANS-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- Q- Electrophilic substitution in case of aromatic amines takes place more readily than benzene. Explain

• ANS- 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 n-butanol 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 n-butanol thus having more tendency to dehydrate.

O-Nitrophenol is more volatile than p-nitrophenol. Why?

Intermolecular hydrogen bonding present in p-nitrophenol helps molecules to associate hence increasing the boiling point. In o-nitrophenol, 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 non-polar.

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 branchedchain 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.

Unlike phenols, alcohols are easily protonated.

Ques-1)

In phenols, the lone pairs of electrons on the oxygen atom are delocalized over thebenzene ring due to resonance & henceare not easily available for protonation.Incontrast in alcohols,the lone pairs of e- on the oxygen atom are localized due to absence of resonance & hence are easilyavailable for protonation.

Ques-2)

How do you account for the fact that unlike phenol, 2,4-dinitrophenol & 2,4,6-trinitrophenol 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 correspondingsodium 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 doublebond character due to resonance & hence cannot be easily cleaved by X- ions in presence of halogen acids or phosphoroushalides to form halobenzenes. In contrast,the C-O bond in alcohols is a pure singlebond & hence can be easily cleaved by X-ions 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 withconc.H2SO4 & not with conc.HCl.

Dehydration of alcohols to form alkenes occurs through carbocationintermediates.If HCl is used, then chloride(Cl-)ion being a good nucleophile bring about substitutionreaction to give an alkyl chloride.IfH2SO4 is used, then the bisulphateion being non-nucleophilic cannotbring about substitution reac.Insteadcarbocation losesa proton to form an

alkene.

Ques-5)

Di-tert-butyl ether cannot be madeby Williamson’s synthesis.Explainwhy?

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 prefersto undergo elimination rather thansubstitution,therefore the product obtained is isobutylene rather thandi-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.Asubsequent nucleophilic attack by astrong nucleophilie such as Br- or I-ion 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 becauseehers 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 cleavedeven by hydrogen chloride at roomtemp to give tert-butyl chloride.Explain.

The di-tert-butyl oxonium ion(I)firstformed by protonation of di-tert-butylether is highly crowded &hence cannot be attacked by the chlorideion.Therfore,it does not undergo cleavage by SN2 mechanism.Insteadit prefers to undergo cleavage by SN1 mechanism since tert-butylcarbocation 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 quantitativeyield by the oxidation of primary alcoholsprovided these are removed from the reacnmixture assoon as they are formed to prevent their further oxidation to carboxylicacids.Since aldehydes having B.P less than 373 K can be easily removed by distillationtherefore,propanal can be easily preparedfrom propanol-1 by distilling it from the alcohol-acid dichromate solution.

Ques-9)

Fluorine is more e-negative than Cleven then, p-flurobenzoic acid is aweaker 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 p-flurobenzoic 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 +R-effect.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 n-butyl 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 p-methoxybenzyl bromide whereas nitro group being electron withdrawing group destabilises carbocation formed by p-nitrobenzyl 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.