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, #"Na"^(+)#, and hydroxide anions, #"OH"^(-)#.

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)|)))#