ka, kb, pka, pkb

Ka, Kb, pKa, pKb

6.3.d calculate and apply the dissociation constant (Ka) and pKa (pKa = -log10 (Ka)) to determine the difference between strong and weak acids

​What we will cover

• what is the acid/base dissociation constant

• calculating review

• how to relate ka and strength of acid

• using ka in pH calculations

​Ka

The same occurs with Kb - just using a weak base

If we were to use a strong acid or base, it is not an equilibrium equation, because the acid or base completely dissociates in solution

​Ka size and relative strength

The Ka of a very strong acid is very large because there is a large concentration of the products and very little of the reactants, which means the numerator of the calculation would be larger than the denominator.


Therefore, the size of Ka gives us information about the degree of dissociation. The larger the Ka, the more dissociation has occurred.

​Ka and pKa relationship

• pKa is the negative log of Ka

  • pKa = -log(Ka)

• so, a high Ka means a low pKa

• Ka is helpful in calculations, like when finding pH

• pKa makes it easy to compare acids

  
  

​Review calculations

We can use these calculations to find concentrations of acids and bases, and then in turn find the Ka, pKa, or pH/pOH

​Example

​Example

​What's next

• Buffers

• End of Module 6!