pH
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pH Calculator: pH, pOH, and Buffers
Convert pH, pOH, hydronium, and hydroxide, solve buffer pH by Henderson-Hasselbalch, and get weak acid or base pH from Ka or Kb with the exact quadratic root and 5% rule check at 25 deg C.
pOH
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| Item | Value |
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pH = -log10[H3O+]; pOH = -log10[OH-]; pH + pOH = 14.000
How?
How this is calculated
At 25 deg C, this tool uses Kw = 1.0e-14. Direct modes convert between pH, pOH, hydronium concentration, and hydroxide concentration. Strong acid and strong base modes multiply concentration by the selected number of equivalents before applying the same logarithms.
Buffer mode applies the Henderson-Hasselbalch equation pH = pKa + log10([A-] / [HA]). A base-form buffer uses the conjugate acid pKa with [A-] set to the base and [HA] set to the conjugate acid.
Weak acid and weak base modes solve the exact quadratic root of the monoprotic model, where [H3O+] = [A-] = x for an acid (or [OH-] = x for a base): x = (-K + sqrt(K^2 + 4 K C0)) / 2. This root neglects water autoionization and holds when K times C0 is much greater than Kw, so the "exact quadratic root" label is scoped to that model. The sqrt(K times C0) approximation and percent ionization are reported beside it, and the page states whether the 5% rule holds.
Formula: pH = -log10[H3O+]; pOH = -log10[OH-]; pH + pOH = 14.000
Sources
- IUPAC Gold Book, pH. IUPAC. Retrieved .
- OpenStax Chemistry 2e, pH and pOH. OpenStax. Retrieved .
- OpenStax Chemistry 2e, Relative Strengths of Acids and Bases. OpenStax. Retrieved .
Method last reviewed