Answer
2.22 x 10⁻⁷ M
Procedure
To calculate the [OH⁻] concentration of blood we will consider the following pH formulas
pH=-log [H₃O⁺]
pH+pOH=14
The pH of blood will be
[tex]pH=-\log_{10}[4.5\times10^{-8}M]=7.3467[/tex]Then we do the rest
[tex]pOH=14-7.3467=6.6532[/tex]Lastly, we transform from pOH to concentration
[tex][OH^-]=10^{-pOH}=10^{-6.6532}=2.22\times10^{-7}[/tex]