Question

Calculate the pH of a solution that is $\mathbf{0}\mathbf{.}\mathbf{20}\mathit{M}\mathit{H}\mathit{O}\mathit{C}\mathit{l}$and $\mathbf{0}\mathbf{.}\mathbf{90}\mathit{M}\mathit{K}\mathit{O}\mathit{C}\mathit{l}$. In order for this buffer to have$\mathit{p}\mathit{H}\mathbf{=}\mathit{p}{\mathit{K}}_{\mathbf{a}}$ would you add $\mathbf{\text{HCl\hspace{0.17em}or\hspace{0.17em}NaOH?}}$what quantity (moles) of which reagent would you add to of the original buffer so that the resulting solution has$\mathit{p}\mathit{H}\mathbf{=}\mathit{p}{\mathit{K}}_{\mathbf{a}}\mathbf{?}$

Short answer

The pH of the solution is$8.14$

The number of moles ofdata-custom-editor="chemistry" $\text{HCl}$ added will bedata-custom-editor="chemistry" $0.35\text{\hspace{0.17em}mol}$

Step-by-step solution

Definition of pH

The pH is a quantitative measure of the acidity or basicity of aqueous or even other liquid solutions.

Calculations

The value of${\text{pK}}_{\text{a}}\text{\hspace{0.17em}is\hspace{0.17em}}7.46$

The value of$\text{pH}=8.14$

Let the number of moles being$\text{x}$

The concentration of both acid and conjugate base needs to be the same

$\begin{array}{l}0.2+\text{x}=0.90-\text{x}\\ \text{2x}=0.7\\ \text{x}=0.35\end{array}$

The pH of the solution is$8.14$ and the number of moles$\text{HCl}$ of added will be$0.35\text{\hspace{0.17em}mol}$