Answer to Question #226857 in General Chemistry for nadia

Question

What is the pH value of a solution of potassium hydroxide whose concentration of hydroxide ions is 0.001 mol dm^-3 ?

Answer 1

What is the pH of a 0.001 mol/dm3 solution of sodium hydroxide?

1 dm3 = 1 cubic decimetre = 1 Litre

So, 0.001 mol/dm3 = 0.001 mol/L = 0.001 M

Now, NaOH ——-> Na+ + OH-

We cannot calculate pH, but pOH is easily calculated in this case.

pOH = - log [molarity of OH-] = - log [ molarity of NaOH] , assuming full dissociation.

Thus, pOH = - log ( 0.001) = - (-3) = 3.

Now, for a solution , pH + pOH = 14

=> pH + 3 =14

=> pH = 11

Thus, the pH of 0.001 mol/dm3 NaOH solution is 11.