pH, pOH to H+ Concentration Online Calculator | Example Problems

If you are working in a chemical or other scientific laboratory, you may need to use a pH meter to find the solution is acidic or basic. When pH or pOH of solution is known, we can readily calculate concentrations of hydronium ion (H₃O⁺) or hydroxyl ion (OH^-) using the pH equation. Also, in this online pH calculator, you have to just substitute pH or pOH value and it will give you what is the H₃O⁺ ion concentration of aqueous solution. Also, several examples are explained with each step of calculation at the end of this tutorial.

Sometimes, H₃O⁺ is denoted as H⁺ and we also use H⁺ term instead of H₃O⁺ term.

There are two calculators in this online calculator.

1. Calculator of pH to H⁺ concentration
2. Calculator of pOH to H⁺ and OH^- concentration

Calculator of pH to H⁺ concentration

This calculator will give H⁺ concentration in mol dm^-3. Ionic product (K_w value) of water is taken as 1 * 10^-14 mol² dm^-6. Therefore, results of this online calculator are very much accurate around 25⁰C.

Calculate

• If you see 'e' in the answer take e = 10, as an example if answer is given as 1e-7, it means 1 * 10^-7
• If answer is given as 1.00005e-5, 1.00005e-5 = 1.00005 * 10^-5

Calculator of pOH to H⁺ and OH^- concentration

This calculator will give H⁺ concentration in mol dm^-3. Here also, results of this online calculator are very much accurate around 25⁰C.

Calculate

Example problems for calculating H⁺ concentration when pH or pOH values are known

What is the H⁺ concentration in an aqueous solution which show pH = 1 ?

Because pH = 1, this solution is a strong acidic solution. We can substitute pH = 1 in pH equation.

• pH = -log[H⁺]
• 1 = -log[H⁺]
• [H⁺] = 0.1 mol dm^-3

What are the H⁺ and OH^- concentrations in pH = 13 solution?

Because pH = 13, this solution is a strong basic solution. We can substitute pH = 1 in pH equation.

• pH = -log[H⁺]
• 13 = -log[H⁺]
• [H⁺] = 1 * 10^-13 mol dm^-3

Because pH + pOH = 14 at 25⁰C.

• pH + pOH = 14
• 13 + pOH = 14
• pOH = 13

From pOH equation, OH^- concentration can be calculated.

• pOH = -log[OH^-]
• 1 = -log[OH^-]
• [OH^-] = 0.1 mol dm^-3

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Variation of pH and H+ ion concentration

Aqueous acetic acid solution has the pH value of 3 and concentration of acetic acid is 0.05 mol dm^-3. What is the H⁺ concentration of acetic acid solution?

Because pH value is given, we can find the H⁺ concentration directly from pH equation.

• pH = -log[H⁺]
• 3 = -log[H⁺]
• [H⁺] = 1 * 10^-3 mol dm^-3

Whether acetic acid concentration is given, we cannot get a direct and easy relationship between acetic acid concentration and H⁺ ion concentration because acetic acid is a weak acid.

In the answer too, you can see H⁺ ion concentration is much lower than acetic acid concentration.

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Questions

Ask your chemistry questions and find the answers

Can I use this calculator for an acid mixture such as HCl and H₂SO₄?

If there are two or more acids in a aqueous solution, all of them give H⁺ ions in different amounts (or in concentrations). So, there is only one H⁺ ion concentration throughout the aqueous solution. So, pH value is uniform throughout the solution. When, we measure the pH value of acidic solution and calculate H⁺ ion concentration, it indicates the overall H⁺ concentration of solution. But, you cannot decide individual concentrations of HCl and H₂SO₄ acids.

If I know pH value of aqueous solution and when I calculate H⁺ ion concentration from pH equation, is it correct for every temperature?

See pH equation. There are only 2 terms in pH equation, H ion concentration and pH value. There is no term for temperature. So, there is no effect for H⁺ ion concentration when it is calculated from pH value in different temperatures.

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