Question

What is the one mole of solute that is contained in one molal solution?
A.1000g of the solvent
B.1000 mL of the solution
C.1 litre of the solvent
D.1000g of the solution

Answer 1

Hint:Molality is the measure of number of moles of solute which are present in one kilo – gram of solvent. It is the ratio of number of moles of solute and mass of the solvent.

Complete step by step answer:
The mass of a substance containing the same number of fundamental units as there are atoms in exactly $12g$ of ${C^{12}}$ is known as the mole of substance.
The measure of the number of moles of solute which are present in 1 kilo – gram of solvent is known as Molality. The S.I. unit of molality is $mol/kg$. Molality can be expressed as the ratio of number of moles of solute and mass of the solvent. It is denoted by $M$. Mathematically, it can be expressed as –
$M = \dfrac{{{n_{solute}}}}{{{m_{solvent}}}}$
where, ${n_{solute}}$ is the number of moles of the solute and ${m_{solvent}}$ is the mass of the solvent in kg.
Molality of one solute in a solution is independent of the presence or absence of other solutes.
One kilo – gram is equal to 1000 gram.
So, the one molal solution contains one mole of solute in 1000 grams of solvent.


Therefore, option (A) is the correct answer.

Note:When the solution is more than one solvent, molality can be defined for the mixed solvent considered as a pure pseudo-solvent. Instead of mole solute per kilogram solvent as in the binary case, units are defined as mole solute per kilogram mixed solvent.