pH
pH of a strong acid or base solution, H+ and OH− concentrations, acidity and indicator colors, with a solution.
What to find:
The concentration can be written in scientific notation: 1e-3 = 0.001 mol/L. Strong acids and bases are assumed to dissociate completely.
The pH calculator finds the pH of a strong acid or base solution from its concentration, the concentrations of H+ and OH− from pH, and tells whether the solution is acidic or basic and how indicators change color.
Formulas
pH = −log[H+], pOH = −log[OH−], pH + pOH = 14
Strong acids (HCl, HNO3, H2SO4) and bases (NaOH, KOH, Ba(OH)2) dissociate completely, so [H+] = c · (number of H+ in the formula) and [OH−] = c · (number of OH groups).
Indicators
| Indicator | Acidic (pH < 7) | Neutral | Basic (pH > 7) |
|---|---|---|---|
| litmus | red | purple | blue |
| methyl orange | red (pH < 3.1) | orange | yellow |
| phenolphthalein | colorless | colorless | crimson (pH > 8.2) |
Example. 0.005 M Ba(OH)2: [OH−] = 2 · 0.005 = 0.01 mol/L, pOH = 2, pH = 14 − 2 = 12.
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