Question

What is the pH of a solution for which [OH-] equals 5.17 x 10^-10 M?

Answer 1

We have to remember two things for this kind of problems

1 pH meaning (it is just a formula) ph is negative logarithm of the concentration of protons (H+) in Molar units

`pH=-\log \lbrack H^+\rbrack`

The secong one is that the concentration of protons [H+] times the concentration of inos OH- [OH-] in aquous solution is always 10 to the minus 14:

`\lbrack H^+\rbrack\lbrack OH^-\rbrack=10^{-14\text{ }}`

then if they give the concentration of ions OH- we can calcuate the concentration of protons and viceversa:

`\lbrack H^+\rbrack=(10^(-14))/(5.17*10^(-10))=1.93*10^(-5)M`

now we have the concentration of protons que only have to apply the pH formula:

`pH=-\log \lbrack H^+\rbrack=-\log (1.93*10^(-5))=4.7`