pOH Calculator

Calculate pOH from hydroxide ion concentration, or find [OH-] from pOH. Determine acid-base character and convert between pH and pOH using pH + pOH = 14 at 25 degrees C.

🔬 Acid-Base📐 pOH = -log[OH⁻]🧪 Chemistry
OH⁻ concentration [OH⁻] (mol/L)
OR pOH value
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
pOH Calculator—pOH = -log[OH⁻]0-14

Step-by-Step Examples

Example 1
NaOH Solution

0.0100 M NaOH (strong base, fully dissociates).

  • [OH-] = 0.0100 M
  • pOH = -log(0.0100) = 2.00
  • pH = 14 - 2.00 = 12.00
✓ pOH = 2.00, pH = 12.00
Example 2
From pOH

pOH = 4.50. Find pH and [OH-].

  • pH = 14 - 4.50 = 9.50
  • [OH-] = 10^-4.50 = 3.16x10^-5 mol/L
✓ pH = 9.50, [OH-] = 3.16x10^-5 M
Example 3
Basic Cleaner

Household cleaner: [OH-] = 0.100 M.

  • pOH = -log(0.100) = 1.00
  • pH = 14 - 1.00 = 13.00
✓ pOH = 1.00, pH = 13.00 (strongly basic)

Real-World Applications

🧪
Strong Base Calculations
NaOH, KOH, Ca(OH)2 fully dissociate; [OH-] calculated directly from concentration.
💊
Medical pH
Blood pH 7.35-7.45 means pOH = 6.55-6.65. Slight variation causes serious medical problems.
🍰
Food Science
Baking soda solutions (pOH ~ 2): understanding basicity for leavening chemistry.
🧼
Cleaning Products
Drain cleaners (NaOH) have very low pOH (high pH). Safety requires understanding of pH/pOH.

Common Mistakes to Avoid

⚠️
pH + pOH = 14 at 25 C only

At 37 C: pH + pOH = 13.62. At 0 C: pH + pOH = 14.94. Only exactly 14 at 25 C.

⚠️
pOH is independent concept

pOH = -log[OH-]. Can calculate pOH without knowing pH first. Then pH = 14 - pOH if at 25 C.

⚠️
Strong vs weak base

Strong base (NaOH): [OH-] = C. Weak base (NH3): [OH-] < C; need Kb for calculation.

Frequently Asked Questions

Why does pH + pOH = 14? ▾
From water equilibrium: Kw = [H+][OH-] = 10^-14 at 25 C. Taking -log: pH + pOH = 14. This is exact at 25 C only.
What is pKw? ▾
pKw = -log(Kw) = 14 at 25 C. Since pH + pOH = pKw: relationship varies with temperature.
What is the pH of 1.0 M NaOH? ▾
[OH-] = 1.0 M. pOH = 0. pH = 14 - 0 = 14. Maximum practical pH.
How do I find pOH from pH? ▾
pOH = 14 - pH (at 25 C). If pH = 8.5: pOH = 5.5. [OH-] = 10^-5.5 = 3.16x10^-6 M.
What is the pOH of neutral water? ▾
Neutral: [H+] = [OH-] = 10^-7. pH = pOH = 7.00. pH + pOH = 14.

Related Chemistry Calculators

🔬 pH Calculator🔬 Ka Calculator🔬 Kb Calculator🔬 Strong Acid pH🧪 Henderson-Hasselbalch

Formula Explorer connections

Interpretation: This relationship connects hydrogen-ion activity, dissociation, conjugate ratios or titration stoichiometry to acid–base behavior. Assumption: Concentration approximates activity mainly in dilute solutions. Temperature, ionic strength, acid strength and equilibrium approximations affect accuracy.

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