Question

How many moles of solute are in a $0.5L$ solution of 3.0 molarity?
A. 1.5 moles solute
B. 4.5 moles solute
C. 6.0 moles solute
D. There is not enough information to solve this problem.

Answer 1

Hint: The composition of the solute and solvent in the solution can be expressed in the terms of its concentration. The terms dilute and concentrated don’t provide a clear idea about the concentration of the solution and thus a quantitative representation is needed for expression of the concentration. The concentration of the solution depends on the amount of solute and solvent that are present in the solution.

Complete step by step answer:
The molarity of the solution can be represented in terms of the volume of the solution rather than the mass of the solvent as in the case of molality. It can be represented as
${{Molarity (M) = }}\dfrac{{{{Moles \;of \;solute}}}}{{{{Volume\; of \;solution\; in\; litre}}}}$
The moles of the compound can be calculated from the equation given as
$Moles = \dfrac{{mass}}{{molar\;mass}}$
3.0 M solution indicates the presence of 3.0 moles in 1.0 L of the solution. 0.5 L of the solution will have $\dfrac{{3.0 \times 0.5}}{1} = 1.5$ moles of the solute.

So the correct answer is A.

Note: There are other representations of the concentration of solution than molarity.
While molality is represented by $m$ another representation, Molarity is represented by $M$ .
Molarity of the solution can be represented in terms of the volume of the solution rather than the mass of the solvent as in case of molality
For the quantitative representation of the concentration of the solution several ways can be used, molality is one of those criteria.
Molality is represented by $m$ and can be calculated by the following formula
$Molality(m) = \dfrac{{{{Moles\; of\; solute}}}}{{{{Mass \;of \;solvent\; in\; kg}}}}$