Solutions MCQ Questions & Answers in Physical Chemistry | Chemistry
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141.
Sprinkling of salt helps in clearing the snow covered roads in hills. The phenomenon involved in the process is
A
lowering in vapour pressure of snow
B
depression in freezing point of snow
C
increase in freezing point of snow
D
melting of ice due to increase in temperature by putting salt.
Answer :
depression in freezing point of snow
When salt is spread over snow, snow starts melting from the surface because of depression in freezing point and helps in clearing the roads.
142.
We have three aqueous solutions of $$NaCl$$ labelled as
$$'A','B'$$ and $$'C'$$ with concentrations $$0.1 M, 0.01M$$ and $$0.001 M,$$ respectively. The value of van't Hoff factor
for these solutions will be in the order
A
$${i_A} < {i_B} < {i_C}$$
B
$${i_A} > {i_B} > {i_C}$$
C
$${i_A} = {i_B} = {i_C}$$
D
$${i_A} < {i_B} > {i_C}$$
Answer :
$${i_A} = {i_B} = {i_C}$$
As $$NaCl$$ is a strong electrolyte, it undergoes dissociation completely. Thus, van't Hoff factor will be same for all these solutions, $${i_A} = {i_B} = {i_C}.$$
143.
During dissolution when solute is added to the solvent, some solute particles separate out from the solution as a result of crystallisation. At the stage of equilibrium, the concentration of solute in the solution at given temperature and pressure
A
increases
B
decreases
C
remains constant
D
keeps changing
Answer :
remains constant
At dynamic equilibrium, number of solute particles going into the solution will be equal to solute particles separating out. Hence, the concentration of solute in the solution remains constant.
144.
Which one of the following modes of expressing concentration is independent of temperature?
A
Molarity
B
Molality
C
Formality
D
Normality
Answer :
Molality
Molality is the best method of expressing concentration of solution because in molality we take mass of solvent which is independent of temperature, so molality of solution is independent of temperature.
145.
The osmotic pressure of a solution can be increased by
A
increasing the volume
B
increasing the number of solute molecules
C
decreasing the temperature
D
removing semipermeable membrane.
Answer :
increasing the number of solute molecules
146.
Which of the following terms has units of temperature ?
$$\eqalign{
& {\text{(i)}}:{K_f} \cr
& {\text{(ii)}}:m{K_f} \cr
& {\text{(iii)}}:i{K_f} \cr
& {\text{(iv)}}:\frac{{m{K_f}}}{i} \cr} $$
A
(i), (ii)
B
(i), (iii)
C
(ii), (iii)
D
(ii), (iv)
Answer :
(ii), (iv)
$$m{K_f} = \Delta {T_f}$$ has the units of temperature . Van’t Hoff factor, $$i,$$ is dimensionless quantity.
147.
Henry's law constant for molality of methane in benzene at $$298\,K$$ is $$4.27 \times {10^5}\,mm\,Hg.$$ The mole fraction of methane in benzene at $$298\,K$$ under $$760\,mm\,Hg$$ is
148.
The elevation in boiling point of a solution of $$9.43\,g$$ of $$MgC{l_2}$$ in $$1\,kg$$ of water is $$({K_b} = 0.52\,K\,kg\,mo{l^{ - 1}},$$ Molar mass of $$MgC{l_2} = 94.3\,g\,mo{l^{ - 1}})$$
149.
For a dilute solution, Raoult’s law states that :
A
the lowering of vapour pressure is equal to the mole
fraction of solute.
B
the relative lowering of vapour pressure is equal to the
mole fraction of solute.
C
the relative lowering of vapour pressure is proportional
to the amount of solute in solution.
D
the vapour pressure of the solution is equal to the mole fraction of solvent.
Answer :
the relative lowering of vapour pressure is equal to the
mole fraction of solute.
$$\frac{{{p^ \circ } - p}}{{{p^ \circ }}} = \frac{{\frac{w}{m}}}{{\frac{w}{m} + \frac{W}{M}}} = {\text{mole fraction of solute}} = {x_B}$$
[ Mathematical statement of Raoult's law ]
150.
If two liquids $$A$$ and $$B$$ form minimum boiling azeotrope at some specific composition then _____________.
A
$$A-B$$ interactions are stronger than those between $$A-A$$ or $$B-B$$
B
vapour pressure of solution increases because more number of molecules of liquids $$A$$ and $$B$$ can escape from the solution
C
vapour pressure of solution decreases because less number of molecules of only one of the liquids escape from the solution
D
$$A-B$$ interactions are weaker than those between $$A-A$$ or $$B-B$$
Answer :
$$A-B$$ interactions are weaker than those between $$A-A$$ or $$B-B$$
The solutions which show a large positive deviation from Raoult's law ( i.e. $$A-B$$ interactions are weaker than those between $$A-A$$ or $$B-B$$ ) form minimum boiling azeotrope at a specific composition.