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 calculate H+ and OH- concentrations easily using 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 H+ ion concentrtion of aqueous solution. Also, a real life examples are explained with calculations step by step at the end of this tutorial.


We have 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. Kw value is taken as 1 * 10-14 mol2 dm-6. Therefore, results of this online calculator are very much accurate around 250C.





Answer

  • 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.




Answer



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



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.




Questions



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. 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.



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.