Chemistry_Today_April_2017_vk_com_stopthepress

47. Assertion : 4 th period of periodic table has 8 elements.
Reason : 4 th period is related with filling of 4s and 4p.
48. Assertion : (SiH 3 ) 3 N has planar shape while (CH 3 ) 3 N
is pyramidal.
Reason : Lone pair of N-atom is used in forming
pπ-dπ bond with Si atom while this bond is
not possible with C-atom which does not have
d-subshell in its valence shell.
49. Assertion : 0.1 M NH 4 OH at 25°C has less conductance
than at 50°C.
Reason : Conductance of a weak electrolyte decreases
with increase in temperature.
50. Assertion : Coagulating power of Al 3+ is more than
Na + .
Reason : Greater the valency of the flocculating ion
added, greater is its power to cause precipitation.
51. Assertion : If edge length of unit cell of LiCl having
NaCl type structure is 5.14 Å, the ionic radius of
Cl – ion is 1.82 Å.
Reason : Anion-anion contact is retained in LiCl
structure because anions constitute the lattice.
52. Assertion : The presence of CO reduces the amount
of haemoglobin available in the blood for carrying
oxygen to the body cells.
Reason : CO combines with haemoglobin about
200 times less easily than oxygen to form complex.
53. Assertion : In the reaction between potassium
permanganate and potassium iodide, permanganate
ions act as oxidising agent.
Reason : Oxidation state of manganese changes
from +2 to +7 during the reaction.
54. Assertion : The radius of second orbit of He + is
equal to that of first orbit of hydrogen.
Reason : The radius of an orbit in hydrogen like
species is directly proportional to n and inversely
proportional to Z.
55. Assertion : CO 2 molecule is linear.
Reason : Dipole moment of CO 2 is zero.
56. Assertion : Superoxides of alkali metals are paramagnetic.
Reason : Superoxides contain the ion O – 2 which has
one unpaired electron.
57. Assertion : Essential oils are purified by steam
distillation.
Reason : Essential oils are volatile and are insoluble
in water.
58. Assertion : All chemicals added to food items are
called food additives.
Reason : All these chemicals increase the nutritive
value of the food.
59. Assertion : In benzimidazole
nitrogens N(I) and N(II) are basic.
II
I
, both the
Reason : Lone pair of electrons present on N(I) is
involved in delocalisation.
60. Assertion : In rate law, unlike in the expression
for equilibrium constants, the exponents for
concentrations do not necessarily match the
stoichiometric coefficients.
Reason : It is the mechanism and not the balanced
chemical equation for the overall change that
governs the reaction rate.
SOLUTIONS
1. (a) : k = 2. 303 a
log
t a−
x
2.2 × 10 –5 2.
303 a
= log
30× 60 a−x
−5
a .
log
a− x
= 22× 10 × 1800
= 0.01719
2.
303
a
= antilog (0.01719) = 1.040
a−
x
a = 1.040a –1.040x
0.040a = 1.040 x
x
a = 0.
040
1 040
= 0. 038 = 38 . %
.
2. (d) : ICl – 4 has four bond pairs and two lone pairs.
Therefore, according to VSEPR theory it should be
square planar. XeF 4 is also square planar in shape.
3. (a) : 96 M atoms are associated with 100 O atoms.
Out of 96 M atoms, suppose M present as M 2+ = x
Then, the number of M 3+ ions will be = 96 – x
Total charge on xM 2+ and (96 – x)M 3+ should be
equal to charge on 100 O 2– ions.
∴ 2x + 3(96 – x) = 100 × 2
2x + 288 – 3x = 200 ⇒ x = 88
CHEMISTRY TODAY | APRIL ‘17 43