ICE Table:
| | CH3CH2CH2CO2H | H3O+ | CH3CH2CH2CO2-|
|:-----:|:-----------------:|:-------:|:-----------------:|
|Initial| 0.055 M | 0 | 0 |
|Change | -x | +x | +x |
|Equil| (0.055-x) M | x M | x M |
Ka Expression:
Ka = [H3O+][CH3CH2CH2CO2-] / [CH3CH2CH2CO2H]
Substitution and Calculation:
2.72 = 10^-pH = 10^-2.72 = 1.90 x 10^-3
Ka = (1.90 x 10^-3)^2 / (0.055 - 1.90 x 10^-3)
Ka = 1.74 x 10^-5