Hydrogen Ion Concentration Calculator

Created by Joanna Śmietańska
Reviewed by Purnima Singh, PhD and Adena Benn
Last updated: Jan 06, 2023

This intuitive and easy-to-use hydrogen ion concentration calculator will help you determine the hydrogen ion concentration [H+] from the pH of the solution. The pH is crucial to determining whether your solution is acidic or basic. Read the text below to find out what is the pOH formula and how to calculate pH from the pOH scale.

What is a hydrogen ion?

Hydrogen ion H+ is also known as a proton. In water, some parts of the molecules have broken into hydrogen ions H+ and hydroxide ions OH-:

H2OH++OHH_2O \rightleftharpoons H^{+} + OH^{-}

You may also encounter a notation as H3O+, i.e. hydronium ion. This is effectively the same as a water molecule H2O combined with a hydrogen ion H+.

In solution, acids decompose into H+ and another anion:

HAH++AHA \rightleftharpoons H^{+} + A^{-}

Alkalies also produce an ion and OH-:

BOHB++OHBOH \rightleftharpoons B^{+} + OH^{-}

Relationship between hydrogen ions and pH

Hydrogen ion concentration is the basis of the pH scale. The number of hydrogen ions determines whether the solution is acidic or basic (also called alkaline). You can check out our dedicated tool to find out how to calculate concentration of the solution in different ways.

Curious about how to find pH from hydrogen ion concentration? You can calculate the pH of the solution as a negative logarithm (base 10) of the hydrogen ion concentration or verify your result with our log calculator:

pH=log([H+])\small pH = -log([H^+])

In a nutshell, an acid is a substance that produces H+ ions in a solution. The base is a substance that produces OH- ions in solution. If hydrogen ions H+ outnumber hydroxide ions OH-, the solution is acidic.

The pH scale ranges from 0 to 14. Pure water is neutral and has a pH value of 7. When pH values are below 7, they correspond to acids, while values above 7 correspond to bases. If you need to maintain the pH at a constant value, use our buffer pH calculator.

How to find hydrogen ion concentration from pH?

Imagine the opposite problem - you have to calculate the ion concentration from the pH value of the solution. Then the hydrogen ion concentration - [H+] will be a power of 10, and a pH is a power number (omit the minus sign when giving the pH value). We used exactly this formula in our hydrogen ion concentration calculator:

[H+]=10pH\small [H^+] = 10^{-pH}

For example, [H+] = 10-6.5 will immediately give a pH value of 6.5. You get the same result if the [H+] ion concentration is written as 0.00000031623 M (or 3.1623 × 10-7 M). M is the number of moles of the substance per liter of solution. Check molarity formula using this calculator.

Note that the more hydrogen ions [H+] the acid provides, the lower the pH.
We are dealing with a logarithmic scale, so every 1.0 decrease in pH means a 10x increase in hydrogen ion concentration, 2.0 gives a 100x increase, and 3.0 a 1000x increase, and so on.

In the other direction, the pH will increase rapidly if the base increases the concentration of OH- ions in the solution and decreases the concentration of [H+] ions.

pOH formula

pOH is a less-known scale for determining the acidity or alkalinity of a solution. Analogous to pH, you can calculate pOH as the negative logarithm of the hydroxide ion OH- concentration:

pOH=log([OH])\small pOH = -log([OH^-])

pH and pOH are related at 25°C, so by knowing one value you automatically get the value of the other:

pH+pOH=14\small pH + pOH = 14

How to use hydrogen ion concentration calculator?

Let's assume we have a solution with a pH of 3.5, and we want to find the [H+] concentration in the solution from the pH of this solution. To do this, use our hydrogen ion concentration calculator:

  1. Enter the pH of 3.5 into the "pH" field.
  2. The concentration of [H+] ion in mol/L is 3.16 × 10-4.
  3. Check the pOH value of the solution, which is 10.5.

Enter any value you know, ph, pOH, or hydrogen ion concentration, and the calculator will calculate the other quantities for you.


What are hydrogen ions?

Hydrogen ions are called protons. Hydrogen is the first element in the periodic table of elements. The hydrogen nucleus is made up of a positively charged particle, called a proton, and an accompanying negatively charged electron. Once an electron is removed, only the H+ proton remains.

Do acids have more hydrogen ions?

Yes, acids have a higher H+ ion concentration than pure water. The stronger the acid, the higher the concentration of hydrogen ions in the solution and, therefore, the lower the pH value.

How can I measure the ph value?

You can use different chemical indicators, e.g., litmus paper, phenolphthalein, or pH meters. Litmus paper will change its color to red in the acids, blue in the alkaline, and purple in the neutral solution. The most reliable but also quite an expensive tool is the pH meter.

How can I find hydrogen ion concentration?

Let's say you have to calculate the number of H+ ions in 100 mL of a solution with a pH of 6. To do this:

  1. Find the [H+] ions concentration: [H+] = 10-pH = 10-6.0 = 1.0×10-6 mol/L.
  2. Write the equation to find moles: moles = molarity (mol/L) × volume (L).
  3. Convert mL to L: 100 mL/1000 = 0.1 L.
  4. Calculate the moles of H+: moles = 1.0×10-6 mol/L × 0.1 L = 1.0×10-7 mol.

How can I find pOH if the hydrogen ion concentration is 0.001 mol/L?

The pOH is 11. Calculate the pH from the equation: pH = -log[H+] = -log[0.001] = 3. Then use the formula which shows the relationship between pH and pOH: pH + pOH = 14 and calculate pOH as 14 - pH = 14 - 3 = 11.

Joanna Śmietańska
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