For strong acids and strong bases, the calculation of [H+ ] and [OH-] depends on the valence and concentration of the strong acid or strong base solution. Look at the following formula.
[H+] = M x acid valence
[OH-] = M x base valence
For weak acid and weak bases, the formula to calculate [H+] and [OH-] of weak acids and weak bases is gained from the equation of acid ionization constant (Ka) and base ionization constant (Kb)
[H+] =
[OH-] =
Relation concentration of H+ and OH- with ionization degree (α) can be shown with the equation as follows:
[H+] = M x α
[OH-] = M x α
Example
Calculate the concentration of OH- in the solution if 8 gr NaOH (Mr=40) dissolved into water until 20 liter!
Mol NaOH= 8gr/40
= 0,2 mol
M NaOH= 0,2 mol/20 L=0,01 M
[OH-]=10-2
