Ka and Kb are equilibrium constants that measure the strength of a weak acid or base. Ka measures the strength of an acid in terms of its ability to donate a proton, while Kb measures the strength of a base in terms of its ability to accept a proton.
Acetic acid is considered a weak acid because it does not completely dissociate in water. Instead, only a small percentage of the molecules dissociate into ions. This results in a lower concentration of hydronium ions in solution, making it a weaker acid compared to strong acids like hydrochloric acid.
The lower the Ka value of an acid, the weaker it is. Acetic acid has a Ka value of only 1.8 x 10^-5, which means it is a weaker acid compared to other acids with higher Ka values. This means that acetic acid is less likely to donate a proton in solution, resulting in a lower acidity.
Kb is lower than Ka for acetic acid because it is a weaker base compared to its conjugate acid, acetate. This means that acetic acid is more likely to accept a proton from water to form its conjugate base, resulting in a lower Kb value.
Similar to Ka, the lower the Kb value of a base, the weaker it is. Acetic acid has a Kb value of only 5.6 x 10^-10, which means it is a weaker base compared to other bases with higher Kb values. This means that acetic acid is less likely to accept a proton in solution, resulting in a lower basicity.