The [OH-] of an aqueous solution is #4.62 * 10^-4# M. What is the pH of this solution?
1 Answer
Explanation:
For pure water at
More specifically, water undergoes a self-ionization reaction that results in the formation of equal concentrations of hydronium and hydroxide anions.
#2"H"_2"O"_text((l]) rightleftharpoons "H"_3"O"_text((aq])^(+) + "OH"_text((aq])^(-)#
At room temperature, the self-ionization constant of water is equal to
#K_W = ["H"_3"O"^(+)] * ["OH"^(-)] = 10^(-14)#
This means that neutral water at this temperature will have
#["H"_3"O"^(+)] = ["OH"^(-)] = 10^(-7)"M"#
As you know, pH and pOH are defined as
#"pH" = - log( ["H"_3"O"^(+)])#
#"pOH" = - log(["OH"^(-)])#
and have the following relationship
#"pH" + "pOH" = 14#
In your case, the concentration of hydroxide ions is bigger than
A pH equal to
So, you can use the given concentration of hydroxide ions to determine the pOH of the solution first
#"pOH" = - log( 4.62 * 10^(-4)) = 3.34#
This means that the solution's pH will be
#"pH" = 14 - "pOH"#
#"pH" = 14 - 3.34 = color(green)(10.66)#
Indeed, the pH is higher than