The objective of this experiment is to determine the exact concentration of an unknown acetic acid solution. To do this, you will perform a titration, a procedure in which controlled volumes of one reagent are added to a flask containing the other reagent until the equivalence point of the reaction is identified. You will use a pH indicator that changes color over a specific range of pH values to help you determine the equivalence point of the titration.
In this experiment, you will perform titrations for two different chemical reactions, one between sodium hydroxide (NaOH) and potassium hydrogen phthalate (KHP) and the other between NaOH and acetic acid (CH3COOH).
NaOH (aq) + KHP (aq) —› Na+ (aq) + K + (aq) + P2- (aq) + H2O (l)
NaOH (aq) + CH3COOH (aq) —› Na+ (aq) + CH3COO- (aq) + H2O (l)
Both reactions are neutralization reactions between a strong base and weak acid. The titration with KHP will allow you determine the exact concentration of the NaOH provided. Knowing the volume of acetic added to the flask and the volume and molarity of the NaOH delivered from the buret to reach the equivalence point, you will calculate the concentration of the unknown solution of acetic acid. At the equivalence point for this 1:1 reaction,
Macid* L acid = Mbase * L base
The phenolphthalein indicator that you add will change from colorless to pink when you have reached the endpoint of the reaction.