pH Calculator
Calculate pH from hydrogen ion concentration or find H+ concentration from pH.
Shows whether a solution is acidic, basic, or neutral.
pH (potential of Hydrogen) is a logarithmic scale measuring how acidic or alkaline a solution is. It ranges from 0 to 14, with 7 being neutral at 25°C.
The pH formula: pH = −log₁₀[H⁺]
Where [H⁺] is the molar concentration of hydrogen ions in moles per liter (mol/L).
Reverse formula — finding H⁺ concentration from pH: [H⁺] = 10^(−pH)
pOH and the relationship: pOH = −log₁₀[OH⁻] pH + pOH = 14 (at 25°C)
Worked example: A solution has [H⁺] = 0.001 mol/L = 10⁻³ mol/L pH = −log₁₀(10⁻³) = −(−3) = pH 3 (acidic)
If pH = 9: [H⁺] = 10⁻⁹ = 0.000000001 mol/L pOH = 14 − 9 = 5
Why logarithmic? The log scale means each whole number step represents a 10× change in acidity. pH 4 is 10× more acidic than pH 5, and 100× more acidic than pH 6.
pH reference scale:
| Substance | pH |
|---|---|
| Battery acid | 0–1 |
| Lemon juice | 2–2.5 |
| Vinegar | 2.9 |
| Coffee | 4.5–5 |
| Pure water | 7.0 |
| Baking soda | 8.3 |
| Milk of magnesia | 10.5 |
| Bleach | 12–13 |
| Drain cleaner | 13–14 |
Buffer solutions resist changes in pH when small amounts of acid or base are added. They are critical in biology — human blood maintains pH between 7.35 and 7.45 very tightly.