pKa [ENDORSED]

[Caitlin Beale 3E]

What is the significance of pKa, how do we determine it, and how is it used?

[Carina H - 2G]

Hi!

pKa is essentially the -log of the Ka value. Only weak acids have Ka values. Generally, the bigger the Ka value, the stronger the weak acid. If the Ka value is large, the pka value is small. They are inversely related. Hope this helps!

[Hannah_Pon_1F]

The pKa value can be compared to the pH to determine what the predominant species present will be in a weak acid solution.
pH = pKa, HA (neutral) = A- (charged)
pH > pKa, HA (neutral) < A- (charged)
pH < pKa, HA (neutral) > A- (charged)

[Anisa Subbiah 14B 1L]

The reason we have pKa and use a logarithmic scale is that it makes the numbers smaller and on a much more easily understandable scale (1-14).