pOH Formula

What is a pOH?

pOH is the criterion for measuring the hydroxide ion concentration in the solution. It is used to determine the basicity of the solution. pOH is equivalent to the negative logarithm of hydroxide ion concentration.

pOH = – log [OH^–]

Table of Content

• The pOH Concept
• pOH Formula
• What is pH?
• Numerical
• Frequently Asked Questions – FAQs

The pOH Concept

pOH is the criterion used to measure the solution’s hydroxide ion concentration. It is used to determine the basicity of the solution. pOH is equivalent to the negative logarithm of hydroxide ion concentration.

pOH = – log [OH^–]

• If the pOH value is less than 7, the solution is basic.
• If the pOH value is equivalent to 7, the solution is neutral.
• If the pOH value is more than 7, the solution is acidic.

pOH Formula

Consider the dissociation of water,

H₂O ⇆ H⁺ + OH^–

The dissociation constant, K_w, would be equivalent to

K_w = [H⁺][OH^–]

Here, K_w refers to the dissociation constant, [H⁺] refers to the hydrogen ion concentration and [OH^–] refers to the hydroxide ion concentration, respectively.

We are taking the negative logarithm of both sides.

-logK_w = -log[H⁺][OH^–]

-logK_w = -(log[H⁺] + [OH^–])

-logK_w = -log[H⁺] -log[OH^–] . . . 1

We know that,

-logK_w = pK_w

-log[H⁺] = pH

-log[OH^–] = pOH

And [H⁺] = [OH^–] = 1 × 10^-7 mol/L

So, equation 1 is equal to

pK_w = pH + pOH

pK_w = 7 + 7

pKw = 14

Or, pH + pOH = 14

Hence if the pH is known, we can quickly determine the value of pOH.

However, in both the pH and pOH scales, 7 is neutral.

What is pH?

pH is the criterion used to measure the solution’s hydrogen ion concentration. It is used to determine the acidity of the solution. pH is equivalent to the negative logarithm of hydrogen ion concentration.

pH = – log [H^–]

• If the pH value is less than 7, the solution is acidic.
• If the pH value is equivalent to 7, the solution is neutral.
• If the pH value is more than 7, the solution is basic.

Numerical

• Calculate the [OH^–] concentration of a solution having pH of 4.42

Given,

pH = 4.42

We know that,

pH + pOH = 14

4.42 + pOH = 14

pOH = 14 – 4.42

pOH = 9.58