Enter the pH value into the calculator to determine the hydroxide ion (OH-) concentration in moles per liter (mol/L).
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OH- Concentration Formula
The following formula is used to calculate the hydroxide ion (OH-) concentration from the pH value (at 25 °C, where Kw ≈ 1.0 × 10−14):
[OH^-] = 10^{pH - 14}Variables:
- [OH-] is the hydroxide ion concentration (mol/L)
- pH is a measure of hydrogen ion activity (often approximated using concentration in dilute solutions)
To calculate the OH- concentration at 25 °C, first find pOH = 14 − pH, then use [OH-] = 10−pOH, which simplifies to [OH-] = 10(pH − 14).
| pH | [OH−] (mol/L) |
|---|---|
| 0 | 1.00e-14 |
| 1 | 1.00e-13 |
| 2 | 1.00e-12 |
| 3 | 1.00e-11 |
| 4 | 1.00e-10 |
| 5 | 1.00e-09 |
| 6 | 1.00e-08 |
| 6.5 | 3.16e-08 |
| 7 | 1.00e-07 |
| 7.2 | 1.58e-07 |
| 7.4 | 2.51e-07 |
| 7.5 | 3.16e-07 |
| 8 | 1.00e-06 |
| 9 | 1.00e-05 |
| 10 | 1.00e-04 |
| 11 | 1.00e-03 |
| 12 | 1.00e-02 |
| 12.5 | 3.16e-02 |
| 13 | 1.00e-01 |
| 14 | 1.00e+00 |
| * Rounded to 3 significant figures. Relation at 25 °C: [OH−] = 10^(pH − 14) mol/L (Kw ≈ 1.0 × 10⁻¹⁴). | |
What is OH- Concentration?
OH- concentration is a measure of the amount of hydroxide ions present in a solution. It is an important parameter in chemistry, particularly in the context of acid-base reactions and pH. The concentration of OH- ions in a solution determines its basicity and is inversely related to the concentration of hydrogen ions (H+), which determines acidity.
How to Calculate OH- Concentration from pH?
The following steps outline how to calculate the OH- Concentration from pH.
- First, determine the pH value of the solution.
- Next, use the formula [OH-] = 10(pH − 14) to calculate the OH- concentration (assumes 25 °C).
- Finally, enter the pH value into the calculator to get the OH- concentration in mol/L.
Example Problem :
Use the following variables as an example problem to test your knowledge.
pH value = 7.0
Using the formula, the OH- concentration is calculated as:
[OH-] = 10(7.0 − 14) = 10-7 mol/L