Question

A molal solution is one that contains one mole of a solute in:
(A)- 1000 g of the solvent
(B)- 1000 mL of the solution
(C)- 1 litre of the solvent
(D)- 1000g of the solution

Answer 1

The concentration of the solution determined by the amount of solute in a certain amount of solvent such that the solution is unaffected by the change of temperature and pressure.

Complete step by step answer:
A molal solution is the concentration of the substance present in the solution. It is the property of solution defined as the amount of solute of the substance to the mass of solvent in which it is dissolved to form the solution.
So, we have the molality defining a relation with respect to the mass of the solvent. It thus acts as an intensive colligative property as the change in temperature and pressure have no effect on the mass. Hence, the molality is not affected and gives a precise measurement of the concentration of substance with ranges of temperature.
The amount of solute is expressed in moles and the mass of solvent in kilograms. Thus, giving the unit of concentration obtained in terms of molality as “m” which is moles per kilogram or $\text{mol}\,\text{k}{{\text{g}}^{\text{-1}}}$.
$Molality,m=\dfrac{\text{moles of solute (in moles) }}{\text{mass of solvent (in kg)}}$

Therefore, a solution with molality of $\text{1}\,\,\text{mol/kg}$ known as 1 molal or 1m, contains one mole of solute So, the correct answer is “Option A”.

Note: The mass in an extensive property dependent on the amount of substance. So, the ratio of the two extensive properties makes the molality intensive in nature.
Also, when the concentration of solution is very low and the water is the only solvent in the solution. We have the molarity of solution related to the volume of solution (in litres) $\text{(= mass of water }\\!\\!\times\\!\\!\text{ density of water)}$where density of water is $\text{1}\,\text{g/mL}$. Then the molality and molarity of the solution have minimal difference, which becomes significantly evident with the increase in the concentration of the solution or density of solvent is different from 1.