Question

The pKa of H2O is 15.7 and the pKa of CH3COOH is 4.8. What label and reason correctly describe a reaction between H2O and CH3COOH?

Answer 1

Answer:

CH3COOH will be the acid, because it is the stronger acid.

Explanation:

When an acid deprotonates in a solution, an equilibrium reaction will occur between the protonated form and the deprotonated form (conjugate base) of it. The equilibrium is characterized by the value of Ka, the equilibrium constant, which is the multiplication of the concentration of the products divided by the concentration of the acid.

As higher is the value of Ka, more acid is deprotonated, and stronger will be the acid. The value of pKa = -logKa, and so, as higher is the Ka, as low is the pKa. Thus, strong acids have low pKa values.

In the reaction of CH3COOH and H2O, the first one has a low value of pKa, so it is a strong acid. The water is a substance that can work as an acid or as a base, and, because of the other substance is a strong acid, it works as a base.