How to Find Hydroxide Ion Concentration

How to Find Hydroxide Ion Concentration
••• Nordroden/iStock/GettyImages

Distilled water weakly dissociates, forming hydrogen (H+) and hydroxide (OH-) ions (H2O = H+ OH-). At a given temperature, the product of molar concentrations of those ions is always a constant: [H+] x [OH] = constant value. The water ion product remains the same constant number in any acid or basic solution. The logarithmic pH scale is commonly used to express the concentration of hydrogen ions. You can easy and accurately measure the pH of the solution with an instrument pH meter as well as estimate it using chemical indicators (pH paper).

    Determine experimentally--for example, with a pH meter--or obtain elsewhere the pH of the solution. For instance, the pH might be 8.3.

    Raise "10" to the power of "-pH" using a calculator to determine the concentration of the hydrogen ions [H+]. In our example [H+] = 10 ^ (-8.3) or 5.01 E-9 (the notation “E-9” means “ten in power -9”).

    Obtain the water ion product at the temperature of interest using the table given in References. Note that in the vast majority of calculations the value of "1 E-14" corresponding to a temperature of 25 Celsius is used.

    Divide the magnitude "1 E-14" by the concentration of the hydrogen ions to determine the concentration of hydroxide ion [OH-]. In our example [OH-] = 1 E-14 / 5.01 E-9 = 2.0 E-6 molar.

Related Articles

How to Calculate the pH of a Two-Chemical Mixture
How to Calculate Theoretical H3O
How to Find the Concentration When You're Given the...
How to Dissolve Magnesium Chloride
How to Calculate Melting & Boiling Points Using Molality
How to Calculate Alkalinity After Titration
How to Calculate Percent Solids by Weight
How to Convert UG/mL to PPM
How to Calculate the Concentration of Ions in a 0.010...
How to Calculate Titratable Acidity
How to Find pH for a Given Molarity
Conversion of PPM to Micromoles
How to Prepare Buffer Solutions
Physical Properties of Household Ammonia
How to Calculate Percent Dissociation
How to Calculate Hydrogen Ion Concentration
How to Calculate Keq Given pKa
How to Convert MG to MEQ
How to Calculate the pH of a Two-Chemical Mixture