Calculate the pH of 0.0765 M KOH
Use this premium KOH pH calculator to determine hydroxide concentration, pOH, and pH for potassium hydroxide solutions. The default setup solves the common chemistry problem: calculate the pH of 0.0765 M KOH at 25 C.
How to calculate the pH of 0.0765 M KOH
To calculate the pH of 0.0765 M KOH, start by identifying what kind of substance potassium hydroxide is. KOH is a strong base, which means it dissociates essentially completely in water under standard introductory chemistry conditions. That complete dissociation is the key reason these pH problems are much easier than weak acid or weak base calculations. When KOH dissolves, each formula unit separates into potassium ions and hydroxide ions:
KOH(aq) -> K+(aq) + OH–(aq)
Because the dissociation ratio is 1:1, the hydroxide ion concentration is numerically equal to the KOH concentration. So if the solution is 0.0765 M KOH, then:
[OH–] = 0.0765 M
Once you know the hydroxide ion concentration, the next step is finding pOH using the standard logarithmic relationship:
pOH = -log[OH–]
Substitute the hydroxide concentration:
pOH = -log(0.0765) = 1.116 approximately
At 25 C, pH and pOH are related by:
pH + pOH = 14.00
Therefore:
pH = 14.00 – 1.116 = 12.884
So the pH of 0.0765 M KOH is 12.884 at 25 C. Rounded to two decimal places, the answer is 12.88.
Why KOH makes pH calculations straightforward
Potassium hydroxide is one of the standard strong bases taught in general chemistry. Unlike weak bases, which establish an equilibrium and require a base dissociation constant, KOH is treated as fully dissociated in ordinary aqueous solutions. That means there is no ICE table needed for this kind of problem. There is also no need to estimate partial ionization, because the chemistry model assumes all KOH contributes hydroxide ions.
This matters because students often overcomplicate the calculation. The direct path is:
- Recognize KOH as a strong base.
- Set hydroxide concentration equal to the molarity of KOH.
- Calculate pOH using the negative log of hydroxide concentration.
- Convert pOH to pH using 14.00 at 25 C.
If your instructor specifies a different temperature, then the relationship between pH and pOH can shift because the ionic product of water changes with temperature. However, unless a problem explicitly states otherwise, chemistry textbook and homework problems almost always assume 25 C.
Core equations used in this calculator
- KOH -> K+ + OH–
- [OH–] = CKOH
- pOH = -log[OH–]
- pH = 14.00 – pOH at 25 C
Step by step worked example for 0.0765 M KOH
Step 1: Write the dissociation
Potassium hydroxide dissociates into one potassium ion and one hydroxide ion. The stoichiometric coefficient for hydroxide is 1, so every mole of KOH yields one mole of OH–.
Step 2: Convert concentration to hydroxide concentration
Since KOH is a strong base and the stoichiometry is 1:1:
[OH–] = 0.0765 M
Step 3: Calculate pOH
Take the negative base-10 logarithm:
pOH = -log(0.0765) = 1.116338…
Step 4: Convert pOH to pH
At 25 C:
pH = 14.00 – 1.116338 = 12.883662
Final answer with proper rounding:
- pH = 12.884 to three decimal places
- pH = 12.88 to two decimal places
Comparison table: pH values for common KOH concentrations
The table below helps place 0.0765 M KOH into context. These values assume complete dissociation of KOH and a temperature of 25 C.
| KOH Concentration (M) | [OH–] (M) | pOH | pH at 25 C |
|---|---|---|---|
| 0.0010 | 0.0010 | 3.000 | 11.000 |
| 0.0050 | 0.0050 | 2.301 | 11.699 |
| 0.0100 | 0.0100 | 2.000 | 12.000 |
| 0.0500 | 0.0500 | 1.301 | 12.699 |
| 0.0765 | 0.0765 | 1.116 | 12.884 |
| 0.1000 | 0.1000 | 1.000 | 13.000 |
Comparison table: strong base examples and expected pH behavior
KOH behaves similarly to other monohydroxide strong bases such as NaOH. The table below compares idealized pH results for several bases under standard classroom assumptions.
| Base | Dissociation pattern | OH– produced per mole | Example concentration | Expected pH at 25 C |
|---|---|---|---|---|
| KOH | Complete | 1 | 0.0765 M | 12.884 |
| NaOH | Complete | 1 | 0.0765 M | 12.884 |
| Ba(OH)2 | Complete | 2 | 0.0765 M | 13.185 |
| NH3 | Partial equilibrium | Less than 1 effective | 0.0765 M | Requires Kb calculation |
Common mistakes when solving the pH of KOH
1. Confusing pH with pOH
One of the most common errors is stopping after calculating 1.116 and reporting that as the pH. That number is the pOH, not the pH. Since KOH is basic, the final pH must be above 7 at 25 C. A result near 1 would indicate a strongly acidic solution, which clearly does not make sense.
2. Forgetting complete dissociation
For KOH in an introductory setting, you should assume complete dissociation. If you treat it like a weak base and try to use an equilibrium table without a justified reason, you will complicate the solution and likely get the wrong answer.
3. Using the wrong logarithm
pH and pOH use the common logarithm, meaning base 10. Be sure your calculator is set to log and not natural log. Using ln will produce an incorrect value.
4. Ignoring significant figures and rounding
If the concentration is given as 0.0765 M, it has three significant figures. Reporting the final pH as 12.883662918 is usually too many digits for a standard chemistry answer. In most class settings, 12.884 or 12.88 is appropriate depending on the required precision.
Why the answer is highly basic
A 0.0765 M KOH solution contains a relatively large hydroxide concentration compared with neutral water. Pure water at 25 C has [H+] and [OH–] each equal to 1.0 x 10-7 M. By contrast, 0.0765 M corresponds to 7.65 x 10-2 M hydroxide, which is hundreds of thousands of times larger than the hydroxide level in neutral water. That large increase drives the pOH down to a little over 1 and pushes the pH up to nearly 12.9.
Quick mental check for the answer
You can estimate whether your result is reasonable without doing the full calculator workflow. Since 0.1 M strong base has pOH = 1 and pH = 13, a concentration of 0.0765 M should give a pOH a little greater than 1 and a pH a little less than 13. The exact result of 12.884 fits that expectation perfectly.
When activity and temperature may matter
In more advanced chemistry, particularly analytical chemistry or physical chemistry, measured pH can differ slightly from the ideal textbook calculation because pH meters respond to hydrogen ion activity rather than simple concentration. At higher ionic strength, activity coefficients can shift the effective values. Likewise, the relation pH + pOH = 14.00 is exact only at 25 C under the standard approximation. These refinements are important in professional laboratory work, but they are not generally required for standard KOH homework problems unless your instructor explicitly introduces them.
Practical notes and safety context
Potassium hydroxide is a strongly caustic substance used in laboratory work, soaps, biodiesel processing, alkaline cleaning, and certain industrial applications. A solution with pH near 12.88 is corrosive to skin and eyes. If you are working with real KOH in a lab, proper PPE, splash protection, and institutional safety procedures are essential. Even though this page is focused on calculation, real chemical handling always requires respect for the hazards of concentrated or moderately concentrated strong bases.
Authoritative chemistry references
Final answer
For a 0.0765 M KOH solution at 25 C, the hydroxide concentration is 0.0765 M, the pOH is 1.116, and the pH is 12.884. If you are asked to round to two decimal places, the answer is 12.88.