J.R. S. answered • 11/24/19

Ph.D. University Professor with 10+ years Tutoring Experience

We are given a solution of NaOH (a strong base) that is 0.0065 M. Because NaOH dissociates into Na^{+} and OH^{-}, the [OH^{-}] will also be 0.0065 M

If we recall that pH + pOH = 14, then if we find pOH, we can easily find pH. The pOH will be the negative log of the [OH-], so that = -log 0.0065 = 2.187

pH = 14 - pOH = 14 - 2.187 = **11.8**

Another way to do this same problem is to first find the [H+] and then take the negative log to get pH. If we recall Kw = 1x10^{-14} = [H+][OH-] we can solve for [H+]....

[H+][OH-] = 1x10^{-14}

[H+] = 1x10^{-14} / 0.0065 = 1.538x10^{-12}

pH = -log 1.538x10^{-12}

**pH = 11.8**