If you have a solution with a [H+ ] of 8.5 x 10 -9 M, what is the pH of the solution to the correct number of significant figures?

Question

I need help with this question

Answer 1

The calculation given is correct, but the question of significant figures has not been addressed.   The [H+] was given to two significant figures.   When taking the log, the integer part is based on the exponent, thus we should use two significant figures for the decimal (mantissa) portion independent of how many significant picutres the integer portion takes up.  8.07 is the correct precision for the pH value.

Answer 2

pH = -log₁₀[H⁺] = -log₁₀(8.5 x 10^-9) ≅ 8.07058