Multiple Choice QuestionsCalculate the energy in joule corresponding to light of wavelength 45mm: (Planck's constant h=6.63 x10-34)Js; speed of light c= 3 x 108 ms-1)
6.67 x 1015
6.67 x 1011
4.42 x 10-15
4.42 x 10-15
D.
4.42 x 10-15
The wavelength of light is related to its energy by the equation,
Which of the following salts will give highest pH in water?
KCl
NaCl
Na2CO3
Na2CO3
C.
Na2CO3
The highest pH refers to the basic solution containing OH- ions. Therefore, the basic salt releasing OH- ions on hydrolysis will give highest pH in water.
Only the salt of a strong base and weak acid would release OH-ion on hydrolysis. Among the given salts, Na2CO3 corresponds to the basic salt as it is formed by the neutralisation of NaOH [strong base] and H2CO3 [weak acid].
which of the following orders of ionic radii is correctly represented?
H- > H >H+
Na+ >F- >O2-
F- > O2->Na+
F- > O2->Na+
A.
H- > H >H+
It is known that radius of the cation is always smaller than that of the neutral atom due to decrease in the number of orbits.Whereas, the radius of the anion is always greater than a cation due to a decrease in effective nuclear charge. Hence, the correct order is
H- > H >H+
Equal masses of H2, O2 and methane have been taken in a container of volume V at temperature 270 C in identical conditions. The ratio of the volumes of gases H2 : O2: CH4 would be
8:16:1
16:8:1
16:1:2
16:1:2
C.
16:1:2
According to Avogadro's hypothesis,
Volume of a gas (V) 
number of moles (n)
Therefore, the ratio of the volumes of gases can be determined in terms of their moles. The ratio of volumes of H2:O2: methane (CH4) is given by
What is the maximum number of orbitals that can be identified with the following quantum numbers?
n=3, l =1, m1 = 0
1
2
3
3
A.
1
The value of n=3 and l =1 suggest that it is a 3p orbital while the value of m1 = 0 [magnetic quantum number] shows that the given 3p orbital is 3pz in nature.
Hence, the maximum number of orbitals identified by the given quantum number is only 1, i.e. 3pz.
For a given exothermic reaction Kp and Kp' are the equilibrium constant at temperatures T1 and T2 respectively. Assuming that heat of reaction si constant in temperature range between T1 and T2 it is readily observed that
Kp> Kp'
Kp< Kp'
Kp = Kp'
Kp = Kp'
A.
Kp> Kp'
The equilibrium constant at two different temperatures for a thermodynamic process is given by
For the reaction X2O4 (l) --> 2XO2 (g) ΔU = 2.1 kcal, ΔS = 20 cal K-1 at 300 K hence ΔG is
2.7 kcal
-2.7kcal
9.3 kcal
9.3 kcal
B.
-2.7kcal
The change in Gibbs free energy is given by
ΔG = ΔH-TΔS
Where, ΔH = enthalpy of the reaction
ΔS = entropy of reaction
Thus, in order to determine ΔG, the values of ΔH must be known. The value of ΔH can be calculated by the equation
ΔH = ΔU + ΔngRT
Where (ΔU) = change in internal energy
Δng = (number of moles of gaseous products)-(number of moles of gaseous reactant) = 2-0 =2
R = gas constant = 2 cal
But, ΔH= Δu + ΔngRT
Δu =2.1 kcal = 2.1 x 103 cal
[1kcal = 103 cal]
therefore,
ΔH = (2.1 x 103) +(2x2x300) =3300 cal
Hence, ΔG = ΔH-TΔS
ΔG = (3300)-(300 x20)
ΔG =-2700 cal
ΔG =-2.7 Kcal
For the reversible reaction,
the equilibrium shifts in the forward direction
by increasing the concentration of NH3 (g)
by decreasing the pressure
by decreasing the concentrations of N2 (g) and H2(g)
by decreasing the concentrations of N2 (g) and H2(g)
D.
by decreasing the concentrations of N2 (g) and H2(g)
Any change in the concentration, pressure and temperature of the reaction results in a change in the direction of equilibrium.This change in the direction of equilibrium in governed by Le-Chatelier's principle. According to Le-Chatelier's principle, the equilibrium shifts in the opposite direction to undo the change.
Increasing pressure and decreasing temperature
On increasing pressure, equilibrium shifts in the forward direction where the number of moles decreases while on decreasing temperature. it will move in a forward direction where temperature increases.
Which of the following statement is correct for the spontaneous absorption of a gas?
B.
ΔS is negative and therefore, ΔH should be highly negativeWhen 22.4 L of H2 (g) is mixed with 11.2 L of Cl2 (g), each of at STP, the moles of HCl (g) formed is equal to
1 mole of HCl (g)
2 moles of HCl (g)
0.5 mole of (g)
0.5 mole of (g)
A.
1 mole of HCl (g)
The given problem is related to the concept of the stoichiometry of chemical equations. Thus, we have to convert the given volumes into their moles and then identify the limiting reagent [possessing minimum number of moles and completely used up in the reaction]
The limiting reagent gives the moles of product formed in the reaction.
