Sodium hydroxide is a strong base with only one hydroxide, so
NaOH ----------> Na+ + OH- and the concentration of hydroxide will be 6.4 x 10^-3
If you log this and change the sign you'll have the pOH. I don't have a calculator handy, but it's obviously two point something (after changing the sign). The question asked for pH however, and pH + pOH = 14 (in water and it does depend on temperature a little) So, if you subtract two point something from 14 you get 11 point something. Looks like 11.8 is the answer.
Answers & Comments
Verified answer
pOH = - log [OH]
pOH = - log (6.40 × 10-3)
pOH = 2.19
pH + pOH = 14
pH = 14 - pOH
pH = 14 - 2.19
pH = 11.8
Sodium hydroxide is a strong base with only one hydroxide, so
NaOH ----------> Na+ + OH- and the concentration of hydroxide will be 6.4 x 10^-3
If you log this and change the sign you'll have the pOH. I don't have a calculator handy, but it's obviously two point something (after changing the sign). The question asked for pH however, and pH + pOH = 14 (in water and it does depend on temperature a little) So, if you subtract two point something from 14 you get 11 point something. Looks like 11.8 is the answer.
the answer: pH = 11.8
-log (6.40 x 10 ^-3 M) = 2.19 = pOH
14 - pOH = pH = 11.8
11.8
pOH = -log(6.40 × 10-3) =2.2
pH = 14 - 2.2 =11.8