KV NO.2, INF LINES, JAMNAGAR
SUBJECT: CHEMISTRY (043)
CLASS: XII
Question
Question
Number
1
Explain giving reasons:
(i) Transition metals and many of their compounds show paramagnetic behavior.
(ii) The enthalpies of atomization of the transition metals are high.
(iii) The transition metals generally form colored compounds.
Marks
1+1+1=3
Answer
(i) Due to presence of unpaired electron
(ii) Because of large number of unpaired electrons in their atoms they have stronger
interatomic interaction and hence stronger bonding between atoms resulting in higher
enthalpies of atomisation.
(iii) Due to d-d transition
2
Explain why:1. Why is N2 less reactive at room temperature?
2. Thereis a large difference between the melting and boiling points of oxygen and
sulphur.
3. Though nitrogen exhibits +5 oxidation state, it does not form pentahalide.
1. Dinitrogen is rather inert at room temperature because of the high bond
enthalpy of N≡N bond.
2. The large difference between the melting and boiling points of oxygen and
sulphur may be explained on the basis of their atomicity; oxygen exists as
diatomic molecule (O2) whereas sulphur exists as polyatomic molecule (S8)
3. Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to
expand its covalence beyond four. That is why it does not form pentahalide.
1+1+1=3
Explain why is orthonitrophenol more acidic than orthomethoxy phenol?
2
Answer
3
The nitro- is an electron withdrawing group .the presence of this group in the ortho
position decreases the electron density .As a result, it is easier to lose a proton.
Also the orthonitrophenoxide ion formed is stabilized by the resonance. Hence,
orthonitrophenol is astronger acid
On the other hand, methoxy group is an electron-releasing group. Thus, it
increases the electron density. Therefore proton cannot be given out easily. So,
orthonitrophenol more acidic than orthomethoxy phenol.
4
(i)Why is it that haloalkanes are more reactive than haloarenes towards nucleophiles.
(ii) Which one of the following reacts faster in an SN1 reaction and why?
2
Answer
(i) In haloarenes C—X bond acquires a partial double bond character due to resonance.
As a result the bond cleavage in haloarenes is difficult than haloalkanes and therefore,
they are less reactive towards nucleophilic substitution reaction.
(ii) Compound (I) reacts faster in SN1 reaction as it is a 2° alkyl halide.
5
State Kohlrausch law of independent migration of ions. Why does the conductivity of a
solution decrease with dilution?
The law states that limiting molar conductivity of an electrolyte can be stated as the sum
of individual contributions of the anions and cations of the electrolyte.
Conductivity of solution decreases as the number of ions per unit volume of the solution
decreases
2
6
Answer
How do you explain the amphoteric behaviour of amino acids?
Amino acids have COOH group and NH2 group. Due to COO—group it is acidic in
nature. Due to NH3+3group it is basic in nature.
2
7
partialhydrolysis
(a)Give the structures of A&B (i) CH 3CH 2 I NaCN
 A OH


 B
Answer
Answer
8
Answer
9
Answer

2 273 K
/ HCl
 A
HNO

 B
(ii) C 6 H 5 NO2 Fe
(b) Ketones are less reactive than aldehydes.Why?
(i) A= CH3CH2CN , B = CH3CH2CONH2 (ii) A = C6H5NH2 , B = C6H5N2Cl
(b) In ketones, there are two electron releasing groups which decrease the +ive charge on
C atom.
Describe the role of ‘Depressents’ in the froth floatation process with the help of an
example.
Depressants are substances that selectively allow sulphide of a particular metal in a
mixture of sulphides to come into the froth while other sulphides are prevented from
coming into the froth. For example, NaCN allows PbS to come into froth and prevents
ZnS from coming into froth.
Why cryolite & fluorospar added to alumina during electrolytic reduction?
Cryolite and fluorospar are added to alumina during electrolytic reduction to reduce
the melting point of alumina and to increase its conductivity
10
Explain the process of refining of Nickel by Mond’s Process
Answer
Nickel is refined by Mond’s process which is based upon vapour phase refining.
In this process nickel is heated in stream of carbon monoxide giving a volatile complex,
leaving the impurities behind. The complex is further subjected to higher
temperature so that it gets decomposed to giving pure metal.
Ni + 4CO --------------> Ni(CO)4
Ni(CO)4 ------------------> Ni + 4CO
2+1=3
2
2
2