Multiple Choice QuestionsBond order of 1.5 is shown by
O2+
O2-
O22-
O22-
B.
O2-
MO configuration of O2+ (8+8-1=15)
50 mL of each gas A and of gas B takes 150 and 200 s respectively for effusing through a pin hole under the similar conditions. If molecular mass of gas B is 36, the molecular mass of gas A will be
96
128
20.2
20.2
C.
20.2
Given,
VA =VB = 50 mL
TA = 150 s
TB = 200 s
MB = 36
MA = ?
From Graham's law of effusion
Maximum number of electrons in a subshell with l =3 and n=4 is
14
16
10
10
A.
14
n represents the main energy level and l represents the subshell.
If n=4 and l = 3, the subshell is 4f.
If f subshell, there are 7 orbitals and each orbital can accommodate a maximum number of electrons, so, maximum number of electrons in 4f subshell = 7 x 2 = 14
Buffer solutions have constant acidity and alkalinity because
these give unionised acid or base on reaction with added acid or alkali
acids and alkalies in these solutions are shielded from attack by other ions.
they have a large excess of H+ or OH- ions
they have a large excess of H+ or OH- ions
A.
these give unionised acid or base on reaction with added acid or alkali
If a small amount of an acid or alkali is added to a buffer solution, it converts them into unionised acid or base. Thus, remains unaffected or in other words its acidity/alkalinity remains constant. e.g.,
H3O+ + A- ⇌ H2O +HA
-OH +HA → H2O +A-
If acid is added, it reacts with A- to form undissociated HA. Similarly, if base/alkali is added, O H- combines with HA to give H2O and A- and thus, maintains the acidity/alkalinity of buffer solution.
pH of a saturated solution of Ba(OH)2 is 12. The value of solubility product Ksp of Ba(OH)2 is
3.3 x 10-7
5.0 x 10-7
4.0 x 10-6
4.0 x 10-6
B.
5.0 x 10-7
Given, pH of Ba(OH)2 = 12
pOH = 14-pH
= 14-12 = 2
We know that,
pOH = -log [OH-]
2 =-log [OH-]
[OH-] = antilog (-2)
[OH-] = 1 x 10-2
Ba(OH)2dissolves in water as 
The correct set four quantum number for the valence electron of rubidium atom (z=37) is
5,1,1, +1/2
6,0,0,+1/2
5,0,0 +1/2
5,0,0 +1/2
C.
5,0,0 +1/2
The enthalpy of fusion of water is 1.435 Kcal/mol. The molar entropy change for the melting of ice of at 0o C is
10.52 cal/(mol K)
21.04 cal/(mol K)
5.260 cal/ (mol K)
5.260 cal/ (mol K)
C.
5.260 cal/ (mol K)
Molar entropy change for the melting of ice,
In which of the following reactions, standard reaction entropy changes (ΔSo) is positive and standard Gibb's energy change (ΔGo) decreases sharply with increasing temperature?
C (graphite) +1/2 O2 (g) → CO (g)
CO (g) +1/2 (g) → CO2 (g)
Mg(s) +1/2O2 (g) → MgO (s)
Mg(s) +1/2O2 (g) → MgO (s)
A.
C (graphite) +1/2 O2 (g) → CO (g)
Among the given reactions only in te case of
C (graphite) +1/2 O2 (g) → CO (g)
entropy increases because randomness (disorder) increases. Thus, standard entropy change (ΔSo) is positive.
Moreover, it is a combustion reaction and all the combustion reactions are generally exothermic, ie. ΔHo=-ve
We know that
ΔGo = ΔHo-TΔSo
ΔGo = -ve-T(+ve)
Thus, as the temperature increases, the value of ΔGo decreases.
Equimolar solutions of the following substances were prepared separately, which one of these will record the highest pH value?
BaCl2
AlCl3
LiCl
LiCl
A.
BaCl2
BaCl2 is a salt of strong acid HCl and strong base Ba(OH)2. So, its aqueous solution is neutral with pH 7. All other salts give acidic solution due to cationic hydrolysis, so their pH is less than 7. Thus, pH value is highest for the solution of BaCl2.
Standard enthalpy of vaporisation ΔvapHθ for water for water at 100oC is 40.66 kJ mol-1. The internal energy of vaporisation of water at 100o C (in KJ mol-1) is
(Assume water vapour to behave like an ideal gas.)
+37.56
-43.76
+43.76
+43.76
A.
+37.56
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