for BHU (MAINS) 2006
28. Ground state electronic configuration of nitrogen atom can be represented by
¥ 1
(i) (2) (3) (4)
t I t t t t
t I
1 1
44 C H E M I S T R Y TODAY | JUNE 06
29. Dipole moment is possessed by (1) 1,4-dichlorobenzene
(2) cz's-1,2-dichloroethene (3) /ra«5-l,2-dichloroethene (4) trans-1,2-dichloro-2-pentene.
30. Which of the following forms ideal solution?
(1) ethyl bromide + ethyl iodide (2) ethyl alcohol + water
(3) benzene + toluene (4) chloroform + benzene.
31. The enthalpy change for the process C (graphite) —» C (g) is called
(1) heat of vaporisation (2) heat of sublimation (3) heat of atomisation.
(4) heat of allotropic change
32. Which of the following statement s) is(are) correct?
(1) The conjugate base of H2P04~ is HP04~.
(2) The pH of 1.0 x IO"8 M HCl solution is 8.
(3) Auto protolysis constant of water increases with temperature.
(4) When a solution of a weak monoprotic acid is titrated against a strong base at half neutralisation point, pH = l/2p Ka.
33. When Cl2 gas is passed through hot NaOH, oxidation number of CI changes from
(1) - 1 to 0 (2) 0 to - 1 (3) 0 to +7 (4) 0 to +5.
34. Which of the following statement/s is/are not correct?
(1) rust is Fe203
(2) saline water slows down rusting
(3) pure metals undergo corrosion faster than impure metals.
(4) Zn-Cu cell is called Daniell cell 35. For a first order reaction
(1) the degree of dissociation is equal to (1 - e~kl) (2) a plot of reciprocal concentration of the reactant
versus time gives a straight line
(3) the pre-exponential factor in the Arrhenius equation has the dimension of time-1.
(4) the time taken for the completion of 75% of the reaction is thrice the tm of the reaction
36. Decrease in atomic number is observed during (1) a-emission (2) positron emission (3) electron capture (4) P-emission.
37. Which of the following pairs of elements have almost similar atomic radii?
(1) Zr, Hf (2) Mo, W (3) Co, Ni (4) Sn, Pb.
38. .^-Hybridisation is found in the structures of (1) 03 (2) NH3 (3) NOj- (4) H20.
39. Highly pure dilute solution of sodium in liquid ammonia
(1) shows blue colour
(2) exhibits electrical conductivity (3) produces sodium amide (4) produces hydrogen gas.
40. Sodium sulphate is soluble in water but barium sulphate is sparingly soluble because
(1) the hydration energy of Na2S04 is more than its lattice energy
(2) the lattice energy of BaS04 is more than its hydration energy
(3) the lattice energy has no role to play in solubility (4) the lattice energy of Na2S04 is more than its
hydration energy.
41. The metals that cannot be obtained by electrolysis of the aqueous solution of their salts are
(1) Ag (2) Mg (3) Cu (4) AI.
42. White phosphorus (P4) has (1) six P - P single bonds (2) four lone pairs of electrons (3) P - P - P angle of 60°.
(4) four P - P single bonds
43. The anodic mud obtained during electrorefining of Cu contains
(1) Ag (2) Fe (3) Au (4) Zn.
44. Tautomerism is exhibited by (1) ( 0 ) - C H = C H - O H
( 4) 0 = Q = 0
45. An aromatic molecule will (1) have (4n + 2) 7t-electrons
(2) be planar (3) be cyclic.
(4) have 4n rc-electrons
46. The greater stability of ter/-butyl carbocation over methyl carbocation can be explained on the basis of (1) +I-effect of the methyl group
(2) hyperconjugation effect of the methyl groups (3) electromeric effect of the methyl groups (4) -I-effect of the methyl groups.
47. When nitrobenzene is treated with Brz in presence of FeBr3, the major product formed is m-bromonitrobenzene. The statements which are related to obtain the m-isomer are
(1) the electron density on meta carbon is more that at ortho and para-positions
(2) the intermediate carbonium ion formed after initial attack of Br+ at the /we?a-positions is least destabilised
(3) loss of aromaticity when Br+ attacks at the ortho and para positions and not at /wefa-position (4) easier loss of H+ to regain aromaticity from the
meta position than from ortho and para positions.
48. /7-Chloroaniline and anilinium hydrochloride can be distinguished by
(1) Sandmeyer reaction (2) NaHC03
(3) AgN03 (4) carbylamine test.
49. Hydroxylamine reacts with
(1) CH3COCl (2) CH3COCH3
(3) CH3COOC2H5 (4) CH3CONH2.
50. Under Wolff-Kishner reduction conditions, the conversions which may be brought about are (1) benzophenone into diphenylmethane (2) benzaldehyde into benzyl alcohol (3) cyclohexanone into cyclohexane (4) cyclohexanone into cyclohexanol.
SOLUTIONS 1. (a) : KA for H202 = 1.55 x 10"12.
2. (a) : Mol. mass of H202 = 2 x 1 + 16 x 2 = 34 Percentage of hydrogen = — xlOO 2
17
100 = 5.88%.3. (b) : Mn+2 2
+4
-*• Mn02 + 2e~
molecular mass _ M Eq. mass change in oxidation number 2 4. (a) : Water has a non-linear while C02 has a linear shape.
5. (c): N2 : KK a(2sf a*(2sf n(2Px)2 n(2Py)2 c(2pzf Bond order = 3
N2+ : KK o(2.?)2 cr*(2.v)2 n(2px)2 n(2P>)2 a(2pz)]
Bond order = 2.
We know that higher the bond order, higher is the bond dissociation energy as well as greater is the stability.
Dissociation energy of N2 > dissociation energy of N2+.
6. (c) : tm = 24 hrs = 1 day X = ^ = 0.693 day'1
t = -hn 2.303
I 2.303
. N0 2.303, 100 l o g — = log
N 0.693 12,5 log8 = 3 days.
7.
8.
0.693
(b) : Zn : Is2 2s2 2p6 3s2 3p" 4s2 3d10
Fe2+ : Is2 2s2 2ph 3s2 3p6 3d6
Ni3+ : l.v2 2.S'2 2p" 3s2 3p6 3d1
Cu+ : Is2 2s2 2p6 3s2 3p6 3dw
(a) : If r is the radius of first orbit, then radius of orbit of the H-atom is rn2.
9. (c) : Magnetic moment = jn(n + 2) B.M Magnetic moment of Ti ion = 1.73 BM
V«(« + 2) =1.73 or, n(n + 2) = 3 or, n = 1.
/. Ti ion has 1 unpaired electron i.e. 3d] configuration.
Complete configuration of Ti3+ ion is Ti3+ (Z = 22) : [Ar]18 3a".
10. (d) : AgCl + 2NH3 [Ag(NH3)2]Cl.
11. (c) : (i = 3 RT M
PL = 3RT\_ / 3R7i p2 V M\ / V M2 Hi I3RT, M2
o r' ^ I MI 3 RT2
TXM2
MXT2
50x32 800x2 = 1.
12. (b) : Molecular mass of NH3 = 17 Molecular mass of HCl = 36.5 Rate of diffusion, r oc 1
molecular mass NH3 will diffuse faster than HCl.
So NH3 vapour will travel a longer distance than HCl vapour in same time.
Ring formed will be nearer to HCl bottle.
13. (b): For gases to show ideal behaviour there should be no attractive or repulsive forces among the molecules.
46 CHEMISTRY TODAY | JUNE 06
14. (b) : A7} = K,x m = 1.86 x 0.5 = 0.93°C A Tf= T°f - Tf
Tj = rf - A7>= 0 - 0.93 = - 0.93°C.
15. (d)
16. (c): When k increases, rate of reaction also increases.
k = - E/RT PZ
For k to increase, P, Z, Tshould increase and E should decrease.
17. (a) : Rate = *[N205] = 6 . 2 x l O ^ x 1.25
= 7.75 x 10-4 mol L-1 s"1. 18. (a) : N2 0 f ) + 3 H2 a f )- » 2 N H3 { l f )
Instantaneous rate = _
4 N2] I d [ u2] l 4 N H3]
dt 3 dt
[salt]
dt 19. (b) : As pOH = pKh + log i
[base]
but [NH4C1] = [NH4OH], pOH = pKh
:. pKh = pOH = 14 - pH = 14 - 9.25 = 4.75 20. (b) : M | M+ \\X~\X
The two half cell reactions for the cell are M M+ + e~
or, X + e~ X~
M+X^> M+ +
X-£°oeii = E°X/X—E°M+/M = 0.33 V - 0.44 V
= - 0.11 V.
As E° ceii is negative the reaction involved is non-spontaneous. The reverse reaction, however, will be spontaneous.
M + + X~ M + X
21. (a) : The strength of their conjugate acids are in the order:
H20 > HC = CH > NH3 > CH3 - CH3
Stronger the acid weaker is its conjugate base. Therefore correct order of strength of their conjugate bases is
CH3 CH,~ > NH,- > HC = C" > OH-22. (d): In SN2 reaction, an optically active alkyl halide gives an optically active product. The product may not have opposite optical rotation to that of the alkyl halide as the two are not enantiomers. Therefore a single stereoisomer is the product.
23. (d): 3CH3CH,OH + PBr3 3CH3CH2Br + H3P03
W 24. (c) : Cu2+ + 4C2H5NH2 [Cu(C2H5NH2)4]2+
tetraethylamine copper(ll) ion (deep blue complex)
25. CHXONH,
CHjCOOH (I)
Br2/KOH ^ PC H2N H j aCH2COOH
p-alanine (II)
26. (a) : 0.1 mol of S02 = 6.4 g
6.02 x 1022 molecules of S02 = 0.1 mol S02 = 6.4 g 1.024 x 1023 molecules of 02 = 0.2 mol 02 = 6.4 g 0.1 mole of 02 = 3.2 g.
27. ( b ) : With increase in temperature, average speed of the molecules as well as rate of collision increases.
28. (c) : In (2) and (4), the unpaired electrons have spin in the same direction.
CI
H - C - CI
29. (c) : [ O J ( H - 0 ) , II (H#0) Y H - C - CI
CI H - C - CI
II (U = 0) CI - C - H
CI CI C H , - C - C 1 I I II C H3- C = C - C H , - C H3 i.e., C 1 - C - C H , C H3
(trans) (M. * 0)
30. (d) : (1) and (3) have pairs of similar liquids. Hence they form ideal solution.
31. (c) : C (() —> C(jf). This process is sublimation as well as conversion of crystalline allotropic form (graphite) to amorphous form (gas carbon).
32. (d)
-1 +5
33. (c) : 3C12 + 6NaOH—> 5NaCl + NaCIO, + 3H,0 . 34. (a) : Rust is Fe203-JcH20. Saline water speeds up rusting. Pure materials almost do not corrode.
35. (d) : Degree of dissociation = 1 - e~k' k = Ae-W'
As EJRT is dimensionless, therefore A has the dimension of k.
36. (a) : Electron capture is addition of . Hence atomic number decreases by one.
37. (a) : Due to lanthanide contraction, the atomic radii of Zr and Hf and Mo and W are almost similar. In case of Co and Ni, the contractive effect of increased nuclear charge is almost balanced by the increase in size due to increasing shielding effect. As a result, the atomic radii of Co and Ni are nearly the same.
38. (c) : NH3 and H20 contain jp3-hybridized N and O atoms respectively.
39. (b) : Dilute solution of Na in liquid NH3 will not produce sodium amide and hydrogen gas instantaneously.
These are metastable and when catalysed give hydrogen and amide.
40. (b): The solubility increases as the hydration energy increases and the lattice energy decreases.
41. (c) : Mg and AI are highly electropositive metals and cannot be obtained by electrolysis of their aqueous salt solutions.
42. (a): White phosphorus (P4) has tetrahedral structure in which each P atom lies at the corners of the regular tetrahedron. There are six single P - P bonds, four lone pairs of electrons and P - P - P bond angle of 60° in the P4 structure.
43. (d) : Noble metals like Ag and Au settle down as anode mud.
44. (a) : (1) shows tautomerism since aldehydes are more stable than vinyl alcohols.
C6H5 - CH = CH - OH •«—?
C6HS - CH2 - CH = O (2) shows tautomerism because enol form is stabilized by aromatic character.
r v o
o
X //
OH OH
(3) shows tautomerism because enol form is stabilized by H-bonding.
q ^ c h
0 O — H
(4) does not show tautomerism because it does not have hydrogens on a saturated carbon at a-positions.
45. (a) : Cyclic planar polyenes containing (4n + 2) Tt-electrons are aromatic in character.
46. (b) : +I-effect and hyperconjugation effect of the CH3 groups.
47. ( b ) : Due to the electron-withdrawing effect of the NO: group, the electron density on m-carbon is more
than that at o- and /^-positions; and the intermediate carbonium ion resulting from meta attack of Br+ is least destabilised. Thus (1) and (2) are correct.
48. (a) : Sandmeyer reaction on p-chloroaniline gives p-dichlorobenzene which is a solid (m.p. 325 K) while that on anilinium chloride gives chlorobenzene which is a liquid (b.p. 405 K).
Sandmeyer
CI NH, reaction
m.p. 325 K.
NH,C1~ Sandmeyer^ < / Q ^c 1
b.p. 405 K reaction
Further, anilinium hydrochloride is an acid salt and hence liberates CO, from NaHC03 and gives white ppt.
of AgCl with AgN03 solution.
C6H5NH3C1 + NaHCO,
C6H5NH3C1 + AgN03
• C02 + H20 + NaCl + C6H5NH2
AgCl + C6H5NH3N07 /7-ChloroaniIine is neither acidic (actually it is basic) nor contains an ionic chlorine and hence does not give the above reactions. Thus (1), (2) and (3) are correct.
However, both p-chloroaniline and anilinium hydrochloride, being 1° amines, give carbylamine test.
O 49. (a) : CH, - C - CI
-HCl
o
IICH3 - c - OC2H5 NH,OH
o II
C H3- C - N H O H
hydroxamic acid
o
C H3- C - N H O H
hydroxamic acid
O C H3- C - C H3
NOH NH;OH
- H , 0 CH3 - C - CH3 oxime
50. (d) : (C6H5)2C = O ™ :h"e r» (C6H5)2CH: benzophenone diphenylmethane
O
Wolff-Kishner reaction
cyclohexanone
•o
cyclohexane4 8 C H E M I S T R Y TODAY | JUNE 06