J.R. S. answered 04/06/17
Tutor
5.0
(145)
Ph.D. in Biochemistry--University Professor--Chemistry Tutor
The definition of pH is the negative log of the [H+], so you need to know to take the negative log of 6.7x10^-6.
Not sure how well you know logs and math, but in case you don't, to take the negative log, just take the exponent (in this case -6) and change the sign and then subtract the log of 6.7.
So, -log 6.7x10^-6 = 6 - log 6.7 = 6 - 0.83 = 5.17 = pH