Answer
a.$[OH^-] = 1.0 \times 10^{-5} \space M $
b. $[OH^-] = 1.0 \times 10^{-8} \space M$
c. $[OH^-] = 5.0 \times 10^{-10} \space M$
d. $[OH^-] = 2.5 \times 10^{-2} \space M$
Work Step by Step
a.$$[OH^-] = \frac{1.0 \times 10^{-14}}{[H_3O^+]} = \frac{1.0 \times 10^{-14}}{ 1.0 \times 10^{-9} } = 1.0 \times 10^{-5} \space M $$
b. $$[OH^-] = \frac{1.0 \times 10^{-14}}{[H_3O^+]} = \frac{1.0 \times 10^{-14}}{ 1.0 \times 10^{-6} } = 1.0 \times 10^{-8} \space M$$
c. $$[OH^-] = \frac{1.0 \times 10^{-14}}{[H_3O^+]} = \frac{1.0 \times 10^{-14}}{ 2.0 \times 10^{-5} } = 5.0 \times 10^{-10} \space M$$
d. $$[OH^-] = \frac{1.0 \times 10^{-14}}{[H_3O^+]} = \frac{1.0 \times 10^{-14}}{ 4.0 \times 10^{-13} } = 2.5 \times 10^{-2} \space M$$
