## Chemistry (7th Edition)

1. Calculate $[H_3O^+]$: $[H_3O^+] = 10^{-pH}$ $[H_3O^+] = 10^{- 7.4}$ $[H_3O^+] = 4 \times 10^{- 8}$ 2. Write the $K_a$ equation, and find the ratio: $K_a = \frac{[H_3O^+][HC{O_3}^-]}{[H_2CO_3]}$ $7.9 \times 10^{-7} = \frac{4 \times 10^{-8}*[HC{O_3}^-]}{[H_2CO_3]}$ $\frac{7.9 \times 10^{-7}}{4 \times 10^{-8}} = \frac{[HC{O_3}^-]}{[H_2CO_3]}$ $20 = \frac{[HC{O_3}^-]}{[H_2CO_3]}$