Question

$5.865g$ of $NaCl$ is dissolved in 500mL of water. What will be the molarity of the solution?
A) $0.1$
B) $0.2$
C) $0.3$
D) $0.4$

Answer 1

We need to know that the molarity (M) indicates the number of moles of solute per liter of solution (moles/Liter) and is one of the most common units used to measure the concentration of a solution. Molarity can be used to calculate the volume of solvent or the amount of solute.

Complete answer:
The concentration of a substance in solution, expressed as the number moles of solute per liter of solution. To calculate the molarity of a solution, the number of moles of solute must be divided by the total liters of solution produced. If the amount of solute is given in grams, we must first calculate the numbers of moles of solute using the solute’s molar mass, then calculate the molarity using the number of moles and total volume. The formula for molarity M is
$M = \dfrac{{mol}}{V}$
The moles of sodium chloride is $5.8558.4 \approx 0.1mol$
The volume of water is $0.51$
So
$M = \dfrac{{0.1}}{{0.5}} = 0.2M$
In thermodynamics the use of molar concentration is often not convenient because the volume of most solutions slightly depends on temperature due to thermal expansion. This problem is usually resolved by introducing temperature correction factors, or by using a temperature-independent measure of concentration such as molality.

Note:
We must know that the molarity is defined as the number of moles of solute per liter of solution. Molality is defined as the number of moles of solute per kilogram of solvent and Normality is defined as the number of equivalents per liter of solution. Molarity is also known as the molar concentration of a solution.