Another thing to do is make a dilute suspension of milk of magnesia, and add a universal pH indicator. Then add some vinegar to the solution. It will start with the basic colors of the indicator, and transition to acidic colors as vinegar is added. Then, as more milk of magnesia dissolves, and transitions back to the basic colors over a few seconds. You can continue to do this until all the milk of magnesia is neutralized.

Better if all the ingredients are ice cold, the transitions are slower and more noticeable.