Calculate H⁺ and OH⁻ concentrations from pH—the scale used to measure acidity and alkalinity.
Solution Input
Ion Concentrations
Enter a pH value to see the corresponding ion concentrations.
About this calculator
Overview
pH is a logarithmic scale that measures the absolute concentration of Hydrogen ions in a solution. Every 1-unit change in pH corresponds to a 10-fold change in concentration. Since water self-ionizes (H₂O ⇌ H⁺ + OH⁻), the concentrations of H⁺ and OH⁻ are always linked—as one goes up, the other must go down to keep their product constant at 10⁻¹⁴.
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Pro Tips
[H⁺] = 10^(-pH) and [OH⁻] = 10^(-pOH). Remember that pH + pOH = 14 at 25°C.
In general, pH < 7 is acidic, pH = 7 is neutral, and pH > 7 is basic (or alkaline).
For every 1 unit pH decrease, the acidity increases by 10 times. A pH 3 solution is 100 times more acidic than pH 5.
The ionic product of water (Kw) increases with temperature, which means the 'neutral' pH point shifts lower as it gets hotter.
Highly concentrated acids can actually have negative pH values (e.g., concentrated HCl can be ~ -1.1).
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Fun Facts
"The 'p' in pH originally stood for 'potenz' (German for power) or 'potentia' (Latin for power), referring to the power of 10."
"Pure water at room temperature has a pH of exactly 7.0, but at 100°C (boiling), its neutral pH is actually around 6.14!"
"A pH of 0 means there is 1 mole of H⁺ ions per liter; a pH of 14 means there is only 0.00000000000001 moles per liter."
"Most soft drinks are about 1,000 to 10,000 times more acidic than pure water."
"Venus has clouds made of sulfuric acid that are estimated to have a pH of roughly -1.2."
"Your skin has a natural 'acid mantle' with a pH of ~4.5 to 5.5, which helps protect against bacteria and fungi."
"Ocean acidification is caused by CO₂ dissolving in the sea, which has dropped the average ocean pH from 8.2 to 8.1 since the Industrial Revolution."
Formula: [H⁺] = 10⁻ᵖᴴ
pH Scale of Common Substances
pH ranges from extremely acidic (0) to extremely basic (14)
Most biological systems require pH between 6-8 for optimal function
