pKa, pH, and Ka

[Kristen_Aguado_2B]

How does pKa relate to an acid and pH? Also, why is Ka is referred to as a constant?

[CristinaG]

Ka is referred to as a constant because its value stays the same for an acid. For example, H2SO4 will always have the same Ka. pKa is the -log of Ka, the association constant, and lets you know how strong the acid is, aka how much it dissociates. Stronger acids have lower pKa values and dissociate more, meaning they are associated with lower/ more acidic pH values

[Vrinda Mahajan 3a]

Ka is a constant because it uses the equilibrium concentrations to calculate acidity, and we already know Kc (which is determined using equilibrium concentrations) is also a constant, so this might help make that easier to understand. pKa indicates how strong an acid is as lower values mean they are more acidic and higher values mean they are less acidic.