pH Calculator

The term pH stands for 'potential of hydrogen' and measures the molar concentration of hydrogen ions in an aqueous solution. Mathematically, pH is defined as the negative base-10 logarithm of the hydrogen ion concentration expressed in moles per liter: pH = -log[H+]. Conversely, if you know the pH, you can find the hydrogen ion concentration using the inverse formula: [H+] = 10^(-pH). In aqueous systems at standard temperature, the relationship between pH and pOH is governed by the ion product of water, meaning that pH + pOH = 14 at 25 degrees Celsius.

Let us walk through calculating the pH of a hydrochloric acid (HCl) solution where the concentration of hydrogen ions [H+] is equal to 0.0025 M. First, apply the logarithmic equation: pH = -log(0.0025). Evaluating the base-10 logarithm of 0.0025 gives approximately -2.602. Multiplying by negative one yields a pH of 2.60. To find the corresponding pOH, subtract this pH value from 14: pOH = 14 - 2.60 = 11.40. This indicates a strongly acidic solution, which aligns with the properties of hydrochloric acid.

Always double-check your units before entering concentrations into the calculator; standard molarity requires moles of solute per liter of solution. Pay close attention to significant figures, as the number of digits after the decimal point in a pH value corresponds to the number of significant figures in the original concentration measurement. Lastly, remember that temperature alters the dissociation constant of water, so these standard calculations are most accurate at 25 degrees Celsius.