Question

8). What is the pH of a fruit with a [–OH] = 3.2  10–9 M –OH?
A) 10.5
B) 8.49
C) 3.51
D) 3.5

Answer 1

You need to know the Kw for water at the temperature of the fruit.

There is a table of Kw versus temperature here

http://www.chemguide.co.uk/physical/acidbaseeqia/kw.html

then use

[H+][OH-]=Kw

to find [H+]

the find pH

Alternatively find
pOH
find pKw

then pH=pKw-pOH