Question

At a certain temperature, the ph of a neutral solution is 7.64. what is the value of kw at that temperature? express your answer numerically using two significant figures.

Answer 1

It is very important to know that neutral pH changes with temperature. The key part to this problem is that the solution is neutral! In a neutral solution the pH and pOH are equal and therefor so are their concentrations. Kw= [H]*[OH] where [H] and [OH] represent the concentrations of those ions. pH=-log[H] antilog(-pH)=[H] Antilog is fancy way of saying 10^x. In our case x=-7.64 [H]=2.95 x 10^-8 M (Molarity) Since pH and pOH are equal in our neutral solution so are their concentrations. [OH]=2.95 x 10^-8 M Now we go back to Kw= [H]*[OH] and plug in the concentrations. Kw=(2.95 x 10^-8)*(2.95 x 10^-8)=8.71 x 10^-16