pH Calculator
How It Works
pH is a logarithmic scale that measures the acidity or basicity of an aqueous solution. It is defined as pH = -log10[H+], where [H+] is the hydrogen ion concentration in moles per liter. The scale runs from 0 (most acidic) to 14 (most basic), with 7 being neutral (pure water at 25 degrees C).
Because pH is logarithmic, each whole number change represents a 10-fold change in hydrogen ion concentration. A solution with pH 3 has 10 times more H+ ions than pH 4, and 100 times more than pH 5. This is why small pH changes can have significant chemical effects.
pH and pOH are complementary: pH + pOH = 14 at 25 degrees C. The product of [H+] and [OH-] always equals 10^-14 (the water dissociation constant Kw). This calculator converts between all four values: pH, pOH, [H+], and [OH-].
Frequently Asked Questions
What is the pH of common substances?
Battery acid: pH 1, lemon juice: pH 2, vinegar: pH 2.5, coffee: pH 5, milk: pH 6.5, pure water: pH 7, blood: pH 7.4, baking soda: pH 8.3, ammonia: pH 11, bleach: pH 12.5.
Why is pH important?
pH affects chemical reactions, biological processes, and material compatibility. Blood pH must stay between 7.35-7.45 for survival. Pool water works best at pH 7.2-7.8. Soil pH determines nutrient availability for plants.
What is the difference between pH and pOH?
pH measures hydrogen ion concentration, while pOH measures hydroxide ion concentration. They are complementary: pH + pOH = 14 at 25°C. An acidic solution has low pH and high pOH, and vice versa.
Can pH be negative or above 14?
Yes, theoretically. Concentrated strong acids can have negative pH values (e.g., concentrated HCl has pH around -1). Very concentrated strong bases can exceed pH 14. However, most practical applications stay within 0-14.