pH Calculator

Understanding pH

pH is a logarithmic scale used to measure the acidity or basicity of a solution. It ranges from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral. The pH equals the negative log base 10 of the hydrogen ion concentration: pH = -log[H+].

This calculator can determine pH from a known acid or base concentration, or calculate all related values (pOH, [H+], [OH-]) from a given pH value.

The pH Scale

Because the pH scale is logarithmic, each whole number change represents a tenfold difference in hydrogen ion concentration. A solution with pH 3 is ten times more acidic than pH 4, and one hundred times more acidic than pH 5. This makes pH a powerful way to express the wide range of acidity found in chemical and biological systems.

• pH 0–2: Strongly acidic (e.g., battery acid, stomach acid)
• pH 3–6: Weakly acidic (e.g., vinegar, coffee, rain water)
• pH 7: Neutral (pure water at 25°C)
• pH 8–11: Weakly basic (e.g., baking soda, soap, ammonia)
• pH 12–14: Strongly basic (e.g., bleach, drain cleaner)

Key Relationships

At 25°C, the ion product of water is Kw = [H+][OH-] = 1.0 × 10¹&sup4;. This means pH + pOH = 14 for any aqueous solution. When you know the pH, the calculator uses these relationships to determine pOH, the hydrogen ion concentration [H+], and the hydroxide ion concentration [OH-].

These calculations are essential in analytical chemistry for titration analysis, buffer preparation, and environmental water quality monitoring.