Enter any one of [H⁺], pH, [OH⁻] or pOH and get the other three, using pH + pOH = 14 at 25 °C.
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From the article pH and pOH Formulas — The Complete Relationship Explained.
Find pH, pOH and [OH⁻] for a solution with [H⁺] = 1.0 × 10⁻³ M.
pH = −log(1.0 × 10⁻³) = 3.00
pOH = 14 − 3.00 = 11.00
[OH⁻] = 10⁻¹¹ = 1.0 × 10⁻¹¹ M
Check with Kw: (1.0 × 10⁻³)(1.0 × 10⁻¹¹) = 1.0 × 10⁻¹⁴. ✔
Find the pH of 0.00200 M HCl.
HCl is a strong acid, so it ionises completely: [H⁺] = 2.00 × 10⁻³ M
pH = −log(2.00 × 10⁻³) = 3 − log 2.00 = 3 − 0.301 = 2.70
Useful shortcut for exam halls without a calculator: log 2 = 0.301, log 3 = 0.477, log 5 = 0.699, log 7 = 0.845. Almost every printed question uses one of these.
Worked in full in pH and pOH Formulas — The Complete Relationship Explained.
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