Lakshya Education MCQs

Question: The vapor density of completely dissociated NH4Cl would be
Options:
 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
: 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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More Questions on This Topic :

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
: B

Correct option is b).
N2O42NO2Initialmoles10

Total moles=0.8+0.4=1.2

Applying, PV=nRT, at constant volume,

P1n1T1=Pn2T2

11X300=P21.2X600

P2=2.4atm.
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%
: C

Correct option is c).
SO2Cl2(g)SO2(g)+Cl2(g)1001ααα
Total moles = 1+α
Pso2Cl2=1α/1+α,Pso2=α/1+α,Pcl2=α/1+α
Kp=(α/1+α)2/(1α/1+α)=α2/1α2α2
α=Kp=(2.9×102=0.17,i.e.,17%
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.
: 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
: C

A+2B2CInitialmoles232Molarconc.2/2=1mol/L3/2=1.5mol/L2/2=1mol/LAtEqui.Conc1+0.25=1.25mol/L1.5+0.5=2mol/L0.5mol/L

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