Department of Chemistry
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.
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. 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 NaOH titration.The phenolphtalein indicator that you add will change from colorless to pink when you have reached the endpoint of the reaction.
For the acetic acid titration, you will measure the initial pH of the acid solution as well as the pH after every addition of NaOH from the buret. By analyzing the "pH versus volume of NaOH added" data, you will identify the equivalence point by finding the point on the titration curve with the steepest slope. Knowing the volume of acetic acid added to the beaker 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 Thymol Blue indicator you add will change from yellow to blue as you near the equivalence point of the reaction. This will help you make sure you are adding the NaOH in small increments near the equivalence point and are able to collect as many pH measurements in that area of the curve as possible.