Question

What volume of 1.5 M HCl solution do you need to use to make 500 mL of 0.25 M HCl solution by dilution?

Answer 1

Hint: To solve this question we first need to know what is molarity. The molarity of a solution can be defined as the concentration of a solute in a solution is in terms of the amount of solute per unit volume, or the molar concentration.

Complete answer:
When a solution is diluted, the number of moles of the solute in the solution remains the same, and just the concentration of the solute decreases.
Now, dilution is the process by which the concentration of a solute can be decreased in a solution by simply adding a solvent like water.
The dilution equation is as follows
${{M}_{1}}{{V}_{1}}={{M}_{2}}{{V}_{2}}$
Where initial molarity is ${{M}_{1}}$, the initial volume is ${{V}_{1}}$, the final molarity is ${{M}_{2}}$ and the final volume is ${{V}_{2}}$.
Now, we need to make a 500 mL of 0.25 M HCl solution from a 1.5 M HCl solution.
So, ${{M}_{1}}$ = 1.5 M, ${{M}_{2}}$ = 0.25 M, and ${{V}_{2}}$ = 500 mL.
We have to find out ${{V}_{1}}$.
Using the formula, we get
\[\begin{align}
  & 1.5\times {{V}_{1}}=0.25\times 500 \\
 & {{V}_{1}}=83.33\text{ mL} \\
\end{align}\]
So, 83.33 mL of 1.5 M HCl solution is needed to make 500 mL of 0.25 M HCl solution by dilution.

Note:
Molarity can be given by
\[M=\dfrac{n}{V}\]
Where M is the molarity of the solution is M, the volume of the solution is V, and the number of moles of solute present in the solution is n.
It should be noted that the SI unit for molarity is mol/${{m}^{3}}$ but it is usually expressed in mol/$d{{m}^{3}}$ which is equivalent to mol/L. It can also be expressed by the capital letter M.