Answer
Molecular weight doesn't match with $K_{a}$
Work Step by Step
According to Appendix D, the result is very close to the $K_{a}$ value of propionic acid, which is $C_{2}H_{5}COOH$
But the molar mass of $C_{2}H_{5}COOH$ is only about $74g/mol$, therefore the molecular weight does not fit.
