When a weak acid solution has common ions added by a salt the equilibrium will shift by Le Chatelier's principle. This shift in equilibrium position that occurs because of the addition of an ion already involved in the equilibrium reaction is called the common ion effect. B. Buffered solution is one that resists a change in its pH when either hydroxide ions or protons are added.
Buffered solutions are simply solutions of weak acids or bases containing a common ion.
When hydroxide ions are added to a buffer solution they react with the acid and are replaced by the Anions. E. Titrations are commonly used to determine the amount of acid or base in a solution. The progress of an acid-base titration is often monitored by plotting the pH of the solution being analyzed as a function of the amount of titrant added. This is called a pH curve. The equivalence point is where the amount of protons is equal to the amount of hydroxide ions.