pH and Kw
|
Water will self ionise according to the equation below. H2O(l) + H2O(l) <=> H3O+(aq) + OH-(aq) Because of self ionisation water will conduct electricity ever so slightly. The equilibrium expression for this equation is given below. But since the concentration of water molecules in an aqueous solution is virtually constant we can write the expression as
In pure water,
at 25oC, the [H3O+] = [OH-]
= 10-7 |
Knowing the hydroxide concentration of a solution we are able to find the pH via the expression above. We can change the expression to solve for the concentration of hydronium ions Or we can change the expression to solve for the concentration of hydroxide ions.
Step 1 find the concentration
of hydronium ions
|