Q18.24P - Chemistry: Molecular Nature Of Matter And Change

Question

(a) What is the ph of ${\mathbf{\text{0.0333 M HNO}}}_{\mathbf{\text{3}}}$? Is the solution neutral, acidic, or basic? 

(b) What is the pOH of $\mathbf{\text{0.0347 M KOH}}$? Is the solution neutral, acidic, or basic?

Step-by-Step Solution

Answer

(a) The value for pH is obtained as $\text{pH = 1.48}$, and the solution is acidic. 

(b) The value for pOH is obtained as $\text{pOH = 1.46}$, and the solution is basic.

Step 1: Definition of pH

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

Step 2: (a) Finding the pH

The number of moles is –

${\text{0.0333 M HNO}}_{\text{3}}$ 

First, let's look at the dissociation reaction of the strong acid ${\text{HNO}}_{\text{3}}$  in water

${\text{HNO}}_{\text{3}}\to {\text{H}}^{\text{ + }}{\text{ + NO}}_{\text{3}}^{\text{ - }}$

The concentration of ${\text{HNO}}_{\text{3}}$ is equal to the sum of the concentrations of $\left[{\text{H}}^{\text{ + }}\right]$ and $\left[{\text{NO}}_{\text{3}}^{\text{ - }}\right]$.

We can solve for the pH using this knowledge.

 $$\begin{gathered} \text{pH = - log}\left[{\text{H}}^{\text{ + }}\right] \\ \text{ = - log(0.0333 M)} \\ \text{pH = 1.48} \end{gathered}$$

The solution is acidic because of the pH<7 .

Therefore, solution is pH = 1.48 , acidic.

Step 3: (b) Finding the pOH

The number of moles is –

 $\text{0.0347 M KOH}$

Let's start with the strong base $KOH$ dissociation process in water.

$\text{KOH}\to {\text{K}}^{\text{ + }}{\text{ + OH}}^{\text{ - }}$

The concentration of $KOH$ is the same as the concentrations of $\left[{\text{K}}^{\text{ + }}\right]$ and $\left[{\text{OH}}^{\text{ - }}\right]$

We can solve for the pOH using this information.

$$\begin{gathered} \text{pOH = - log}\left[{\text{OH}}^{\text{ - }}\right] \\ \text{ = - log(0.0347 M)} \\ \text{pOH = 1.46} \end{gathered}$$

The solution is simple because pOH<7 .

Therefore, solution is pOH = 1.46, basic.