Q18.23P - Chemistry: Molecular Nature Of Matter And Change

Question

(a) What is the pH of $\mathbf{0}.\mathbf{0111}\mathbf{M}\mathbf{NaOH}$? Is the solution neutral, acidic, or basic? (b) What is the pOH of $\mathbf{1}\mathbf{.}\mathbf{35}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{3}}\mathbf{ }\mathit{M}\mathbf{ }\mathit{H}\mathit{C}\mathit{l}$? Is the solution neutral, acidic, or basic?

Step-by-Step Solution

Answer

(a) The value for pH is obtained as  $\text{pH = 12.05}$, and the solution is basic.

(b) The value for pOH is obtained as $\text{pOH = 11.13}$ , and the solution is acidic.

Step 1: Definition of pH

The negative logarithm of ${\mathbf{\text{H}}}^{\mathbf{\text{ + }}}$ ion concentration is used to calculate pH. As a result, the meaning of pH is justified as hydrogen power.

Step 2: (a) Finding the pH

Let's start with the strong base's dissociation reaction. In water, $\text{NaOH}$

$\text{NaOH}\to {\text{Na}}^{\text{ + }}{\text{ + OH}}^{\text{ - }}$

The concentration of $\text{NaOH}$ is equal to the sum of the concentrations of $\left[{\text{Na}}^{\text{ + }}\right]$ and $\left[{\text{OH}}^{\text{ - }}\right]$.

We can solve for the pOH using this information.

$$\begin{gathered} \text{pOH = - log}\left[{\text{OH}}^{\text{ - }}\right] \\ \text{ = - log(0.0111 M)} \\ \text{pOH = 1.95} \end{gathered}$$

We can solve it using the equation below because we're seeking for its pH.

$$\begin{gathered} \text{pOH + pH = 14} \\ \text{pH = 14 - pOH} \\ \text{ = 14 - 1.95} \\ \text{pH = 12.05} \end{gathered}$$

The solution is simple because pH>7 .

Therefore, Solution is pH=12.05 , basic.

Step 3: (b) Finding the pOH

The number of moles is –

$1.35\times {10}^{-3} M HCl$

First, let's look at how the strong acid HCl dissociates in water.

$\text{HCl}\to {\text{H}}^{\text{ + }}{\text{ + Cl}}^{\text{ - }}$

We can solve for the pH using this information. 

$$\begin{gathered} \text{pH = - log}\left[{\text{H}}^{\text{ + }}\right] \\ \text{=-log}\left(1.35\times {10}^{-3} M\right) \\ pH=2.87 \end{gathered}$$

 Since we're seeking for its OH, we'll use the equation below to solve it.

$$\begin{gathered} \text{pOH + pH = 14} \\ \text{pOH = 14 - pH} \\ \text{ = 14 - 2.87} \\ \text{pOH = 11.13} \end{gathered}$$

The solution is acidic because of the pH<7.

Therefore, Solution pOH = 11.13 is , acidic.