Lakshya Education MCQs

Question: The vapor density of completely dissociated NH4Cl would be
A.same as that of NH4Cl
B.double than that of NH4Cl
C.half than that of NH4Cl
D.slightly less than that of NH4Cl
Answer: Option A
: A

On dissolution of NH4Cl into NH3+HCl number of moles become double. Hence, volume is doubled and therefore, density is halved.

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Question 1. 1 mole of N2 O4 (g) at 300K is kept in a closed container under 1 atm pressure. It is heated to 600K when 20% by mass of N2O4 (g) decomposes to NO2 (g) . The resultant pressure is
  1.    1.2 atm
  2.    2.4 atm
  3.    2.0 atm
  4.    1.0 atm
Answer: Option B
: B

Correct option is b).

Total moles=0.8+0.4=1.2

Applying, PV=nRT, at constant volume,



Question 2. At 30C,Kp for the dissociation reaction:

SO2Cl2 (g) SO2 (g) + Cl2 (g) is 2.9x 102~atm. If the total pressure is 1 atm, the degree of dissociation of SO2Cl2 is (assume 1α2 =1)
  1.    85%
  2.    12%
  3.    17%
  4.    35%
Answer: Option C
: C

Correct option is c).
Total moles = 1+α
Question 3. If concentration of OHions in the reaction  Fe(OH)3(s)  Fe3++(aq)+ 3 OH (aq) is decreased by 1/4 times, then equilibrium concentration of Fe3+will increase by
  1.    8 times
  2.    16 times
  3.    64 times
  4.    4 times.
Answer: Option C
: C

K=[Fe3+][OH]3 If concentration of OHion is decreased to 14 th to keep K constant
Concentration of Fe3+ions has to be increased by 64 times.
Question 4. In a reaction A+2B  2C; 2 moles ofA, 3 mole of B and 2 mole of C are placed in a 2 L flask and the equilibrium concentration of C is 0.5 mole/L. The equilibrium constant K for the reaction is:
  1.    0.073
  2.    0.147
  3.    0.05
  4.    0.026
Answer: Option C
: C


K=(0.5)2/(1.25×(2)2)=0.05 Note that concentration of C has decreased, i.e., to attain equilibrium, reaction has shifted backwards. Decrease in conc. of C will be 0.5mol/L and hence increase in concentration of B will be 0.5mol/L and that of A will be 0.25mol/L
Question 5. At a certain temperature and a total pressure of 105 Pa, iodine vapours contain 40 % by volume of iodine atoms

[I2(g)  2 I(g)]. Kp for the equilibrium will be
  1.    0.67
  2.    1.5
  3.    2.67 × 104
  4.    9.0 × 104
Answer: Option C
: C

Partial pressure of I atoms

Partial pressure of l2(p2)=60×105/100Pa=0.6×105Pa

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