# Question #ba1d8

Aug 27, 2016

$\text{100 mL HCl}$

#### Explanation:

You're mixing hydrochloric acid, $\text{HCl}$, a strong acid, and potassium hydroxide, a strong base, so right from the start you know that in order to have a final solution of pH equal to $7$, a complete neutralization must take place.

In other words, you need to add enough acid to make sure that the base is completely neutralized.

The balanced chemical equation that describes this neutralization reaction looks like this

${\text{HCl"_ ((aq)) + "KOH"_ ((aq)) -> "KCl"_ ((aq)) + "H"_ 2"O}}_{\left(l\right)}$

Notice that you need $1$ mole of hydrochloric acid to neutralize $1$ mole of potassium hydroxide.

Now, you know that you the potassium hydroxide solution has a volume of $\text{100 mL}$ and a molarity of $\text{2.00 M}$. As you know, molarity is a measure of a solution's concentration in terms of moles of solute present in one liter of solution.

Even without doing any calculations, you should be able to say that in order to get a solution of pH equal to $7$, you must add $\text{100 mL}$ of your $\text{2.00 M}$ hydrochloric acid solution to the given potassium hydroxide solution.

As you can see, both solutions have the same molarity. This implies that equal volumes of these two solutions will contain the same number of moles of solute.

Therefore, you can say that the volume of $\text{2.00 M}$ hydrochloric acid solution needed to neutralize $\text{100 mL}$ of $\text{2.00 M}$ potassium hydroxide solution will be

$\textcolor{g r e e n}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{\text{volume of HCl " = " 100 mL}} \textcolor{w h i t e}{\frac{a}{a}} |}}}$