Predicting Acid and Base Equilibrium

The holy grail of acid-base chemistry is to be able to draw the mechanism and predict the equilibrium for an acid-base reaction. Believe it or not, you’re ready to do this. 

STEP 1. Identify the acid and base

  • Many times charges or a known acid will be present (+) = Acid ( -) = Base
  • If you see no charges, dissociate ALL spectator ions, these are the cations Li+, Na+, K+  and Cs+
  • If both compounds are still neutral, assign the one with the lowest pKa as the acid.

STEP 2. Label the conjugate acid and base. Remember:

  • Acids LOSE their most acidic proton to become conjugate bases
  • Bases GAIN a proton to become conjugate acids

STEP 3. Compare the acidity/pKa of the acid to the conjugate acid. The equilibrium will favor the side with the weaker acid (arrow towards the highest pKa)

That’s all there is to it! Watch me solve the first example so you can get the hang of it. 

Example: Would the following reaction go to the right or left? Label ALL species. Draw arrows in the correct direction.

4m

This next one is all you.

Example: Would the following reaction go to the right or left? Label ALL species. Draw arrows in the correct direction.

3m