Calculate Poh and Ph for Each of The Following

This guide explains how to calculate pOH and pH for different solutions, including acids, bases, and buffers. We'll cover the formulas, provide practical examples, and show you how to use our calculator for quick results.

What is pOH and pH?

pH and pOH are measures of the acidity or basicity of a solution. They are logarithmic scales that indicate the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) in a solution.

The pH scale ranges from 0 to 14, where:

pH 0-6: Acidic solutions
pH 7: Neutral solution (pure water)
pH 8-14: Basic solutions

The relationship between pH and pOH is defined by the equation:

pH + pOH = 14

This means that for every solution, knowing one value allows you to calculate the other.

How to Calculate pOH and pH

Calculating pH from pOH

If you know the pOH value, you can calculate pH using the formula:

pH = 14 - pOH

Calculating pOH from pH

Similarly, if you know the pH value, you can calculate pOH using:

pOH = 14 - pH

Calculating pH from Hydrogen Ion Concentration

For solutions where you know the concentration of hydrogen ions [H⁺], use the formula:

pH = -log[H⁺]

Calculating pOH from Hydroxide Ion Concentration

For solutions where you know the concentration of hydroxide ions [OH⁻], use:

pOH = -log[OH⁻]

Examples

Let's look at some examples to see how these calculations work in practice.

Example 1: Calculating pH from pOH

If a solution has a pOH of 3.5, what is its pH?

pH = 14 - pOH = 14 - 3.5 = 10.5

Example 2: Calculating pOH from pH

If a solution has a pH of 8.2, what is its pOH?

pOH = 14 - pH = 14 - 8.2 = 5.8

Example 3: Calculating pH from Hydrogen Ion Concentration

If a solution has a hydrogen ion concentration of 1 × 10⁻⁵ M, what is its pH?

pH = -log(1 × 10⁻⁵) = -(-5) = 5

Example 4: Calculating pOH from Hydroxide Ion Concentration

If a solution has a hydroxide ion concentration of 2 × 10⁻⁴ M, what is its pOH?

pOH = -log(2 × 10⁻⁴) = -(-3.699) ≈ 3.7

Given Value	Calculation	Result
pOH = 3.5	pH = 14 - 3.5	pH = 10.5
pH = 8.2	pOH = 14 - 8.2	pOH = 5.8
[H⁺] = 1 × 10⁻⁵ M	pH = -log(1 × 10⁻⁵)	pH = 5
[OH⁻] = 2 × 10⁻⁴ M	pOH = -log(2 × 10⁻⁴)	pOH ≈ 3.7

FAQ

What is the difference between pH and pOH?

pH measures the concentration of hydrogen ions (H⁺), while pOH measures the concentration of hydroxide ions (OH⁻). They are related by the equation pH + pOH = 14.

How do I calculate pH from pOH?

Use the formula pH = 14 - pOH. For example, if pOH is 3.5, then pH is 10.5.

How do I calculate pOH from pH?

Use the formula pOH = 14 - pH. For example, if pH is 8.2, then pOH is 5.8.

What is the pH of pure water?

The pH of pure water is 7, which is neutral. At this pH, the concentration of H⁺ and OH⁻ ions is equal.

How do I calculate pH from hydrogen ion concentration?

Use the formula pH = -log[H⁺]. For example, if [H⁺] is 1 × 10⁻⁵ M, then pH is 5.