The number of moles of KMnO4 reduced by one mole of KI in alkaline medium is
one-fifth
five
one
two
D.
two
In alkaline solution, KMnO4 is reduced to MnO2 (colourless).
Hence, two moles of KMnO4 are reduced by one mole of KI.
Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction?
Exothermic and decreasing disorder
Endothermic and increasing disorder
Exothermic and increasing disorder
Endothermic and decreasing disorder
C.
Exothermic and increasing disorder
If a reaction is exothermic, H will be -ve and in increasing order, S will be +ve thus, at this condition, G is negative according to following equation:
G = H - TS
G = -ve.
Hence, for spontaneous reaction G must be -ve
A nuclide of an alkaline earth metal undergoes radioactive decay by emission of three -particles in succession. The group of the periodic table to which the resulting daughter element would belong to
Group 14
Group 16
Group 4
Group 6
A.
Group 14
After decay of radioactive element, the last element Pb is obtained which belongs to group 14 of periodic table.
Which of the following molecules has trigonal planar geometry?
IF3
PCl3
NH3
BF3
D.
BF3
Among all the given options, IF3 has trigonal planar geometry.
PCl3 has pyramidal geometry.
NH3 has pyramidal geometry.
BF3 has trigonal planar geometry
The absolute enthalpy of neutralisation of the reaction
MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)
will be
less than - 57.33 kJ mol-1
- 57.33 kJ mol-1
greater than-- 57.33 kJ mol-1
57.33 kJ mol-1
A.
less than - 57.33 kJ mol-1
Heat of neutralisation of strong acid and strong base is -57.33 kJ. MgO is weak base while HCl is strong acid, so the heat of neutralisation of MgO and HCl is lower to -57.33 kJ because MgO requires some heat in ionisation, then net released amount of heat is decreased.
Which of the following is the electron deficient molecule?
B2H6
C2H6
PH3
SiH4
A.
B2H6
B2H6 is electron deficient molecule because boron atom has three half filled orbitals in excited state. The structure of B2H6 is represented as follows :
In it two electrons of a B - H bond are involved in formation of three centre bond, these bonds are represented as dotted lines.
The mass of carbon anode consumed (giving only carbondioxide) in the production of 270 kg of aluminium metal from bauxite by the Hall process is (Atomic mass Al= 27)
180 kg
270 kg
540 kg
90 kg
D.
90 kg
In Hall and Heroult process
2Al2O3 4Al + 3O2
4C + 3O2 2CO2 + 2CO
2Al2O3 + 4C 4Al + 2CO2 + 2CO
Only for removal of CO2, following equation is possible
2Al2O3 + 3C 4Al + 3CO2
Molecular weight of Carbon = 12
Molecular weight of Aluminium = 27
For Carbon/ C = 3 x 12 = 36
For Aluminium/ Al = 4 x 27 = 108
For 108 gm of Al, 36 gm of C is required in above reaction
For 270 gm of Al require amount of C =
A reaction occurs spontaneously if
TS < H and both H and S are +ve
TS > H and both H and S are +ve
TS = H and both H and S are +ve
TS > H and H is +ve and S is - ve
B.
TS > H and both H and S are +ve
The spontaneity of reaction is based upon the negative value of G, G is based upon T, S and H according to the following equation (Gibbs-Helmholtz equation):
If the magnitude of H - TS is negative, then the reaction is spontaneous.
When TS > H and H and S are +ve, then G is negative.
The correct sequence of increasing covalent character is represented by
LiCl < NaCl < BeCl2
BeCl2 < NaCl < LiCl
NaCl < LiCl < BeCl2
BeCl2 < LiCl < NaCl
C.
NaCl < LiCl < BeCl2
According to Fajan's rule, lower the size of cation higher will be its polarising power and higher will be covalent character.
Polarising power
Covalent character Polarising power
So, the correct order is NaCl < LiCl < BeCl2
Equilibrium constants K1 and K2 for the following equilibria
NO (g) + NO2(g) and
2NO2(g) 2NO (g) + O2(g)
are related as
D.
(i) NO (g) + (g) NO2(g)
So, K1 = ...(1)
(ii) 2NO2 (g) 2NO + O2 (g)
So, K2 = ...(2)
From equation (1)
or
...(3)
from equation (2) and (3)
K2 =