Question

In which mode of expression, the concentration of a solution remains independent of temperature?
A.Molarity
B.Normality
C.Formality
D.Molality

Answer 1

Hint: The volume of solution is directly proportional to the temperature. Thus, as the temperature increases, volume of the solution also increases. Thus, the concentration of any solution that depends on the volume of the solution varies directly with temperature.

Complete step by step answer:
The number of moles of a solute per liter of a solution is known as molarity.
${\text{Molarity}}\left( {\text{M}} \right)\, = \dfrac{{{\text{Moles}}\,{\text{of}}\,{\text{solute}}\left( {{\text{mol}}} \right)}}{{{\text{Volume}}\,{\text{of}}\,{\text{solution}}\left( {\text{L}} \right)}}$
The molarity of a solution is inversely proportional to the volume of the solution. And the volume is directly proportional to the temperature. Thus,
${\text{M}} \propto \dfrac{1}{{\text{V}}} \propto \dfrac{1}{{\text{T}}}$
Thus, the molarity of a solution varies indirectly with temperature.
Step 2:
The number of moles of a solute per liter of a solution is known as molarity.
For acids,
${\text{Normality}}\left( {\text{N}} \right)\, = {\text{Molarity}} \times {\text{Basicity}}$
Where basicity is the number of ${{\text{H}}^ + }$ ions given out by an acid molecule.
For bases,
${\text{Normality}}\left( {\text{N}} \right)\, = {\text{Molarity}} \times {\text{Acidity}}$
Where acidity is the number of ${\text{O}}{{\text{H}}^ - }$ ions given out by a base molecule.
The normality of a solution depends on the molarity which is inversely proportional to the volume of the solution. And the volume is directly proportional to the temperature. Thus,
${\text{N}} \propto {\text{M}} \propto \dfrac{1}{{\text{V}}} \propto \dfrac{1}{{\text{T}}}$
Thus, the normality of a solution varies indirectly with temperature.
Step 3:
The number of formula mass of a solute per liter of a solution is known as formality.
${\text{Formality}}\left( {\text{F}} \right) = \dfrac{{{\text{Number of formula mass}}}}{{{\text{Volume of solution}}\left( {\text{L}} \right)}}$
The formality of a solution is inversely proportional to the volume of the solution. And the volume is directly proportional to the temperature. Thus,
${\text{F}} \propto \dfrac{1}{{\text{V}}} \propto \dfrac{1}{{\text{T}}}$
Thus, the formality of a solution varies indirectly with temperature.
Step 4:
The ratio of the number of moles of solute to the mass of solvent in kilograms is known as molality.
${\text{Molality}}\left( {\text{m}} \right) = \dfrac{{{\text{Number of moles of solute}}\left( {{\text{mol}}} \right)}}{{{\text{Mass of solvent}}\left( {{\text{kg}}} \right)}}$
The moles of solute and mass of solvent do not vary with temperature. Thus, molality of a solution does not vary with temperature.
Thus, in molality, the concentration of a solution remains independent of temperature.

So, the correct answer is Option D .

Note:
The concentration of any solution that depends on the volume of the solution varies directly with temperature.Molality of any solution does not depend on temperature because it involve mass