What is the pH of a 0.0605 M solution of sodium hydroxide, #NaOH#?
You're dealing with a solution that contains a strong base, so right from the start you should know that sodium hydroxide dissociates completely in aqueous solution to produce sodium cations,
This means that for every mole of sodium hydroxide that you're dissolving in water, you will get one mole of hydroxide anions in aqueous solution.
Therefore, for a given volume of your solution, the concentration of the hydroxide anions will be equal to that of the strong base
#["OH"^(-)] = ["NaOH"] = "0.0605 M"#
Now that you know the concentration of hydroxide anions, you can calculate the pOH of the solution by using
#color(blue)(|bar(ul(color(white)(a/a)"pOH" = - log(["OH"^(-)])color(white)(a/a)|)))#
Plug in your value to find
#"pOH" = - log(0.0605) = 1.22#
You know that for aqueous solutions at room temperature you have
#color(blue)(|bar(ul(color(white)(a/a)"pOH " + " pH" = 14color(white)(a/a)|)))#
Plug in the pOH of the solution to get
#"pH" = 14 - 1.22 = color(green)(|bar(ul(color(white)(a/a)color(black)(12.78)color(white)(a/a)|)))#