Acid-Base Titration Lab Report

Madison Guido

Determination of Ka : Titration of Weak Acid

Introduction/Theory:

The purposed of this experiment is to use a LoggerPro and LabPro to follow the pH changes during an acid-base titration, and ultimately determine the Ka, through calculation, of the weak-acid (acetic acid or vinegar, HC2H3O2) being titrated. Ka can be defined as a constant for a given acid at any temperature. Generally, in water solutions, weak acids react with water to establish equilibrium, for example:

HA + H2O ⇄ H3O+ + A-

This equilibrium is represented by Ka, or the acid dissociation constant, in which:

Ka = [H3O+]aq x [A-]aq/ [HA]aq

The Ka of an acid can be calculated in two ways, including (1) the measurement of the pH of a solution containing a know concentration of a weak acid, and (2) measurement of the pH at the

Error:

Theoretical Ka of HC2H3O2: 1.75 x 10-5

Error of Ka from pH of original solution: 60.5%

% Error = [|Theoretical Ka - Experimental Ka |/Theoretical Ka] x 100

% Error = [|6.92 x 10-6- 1.75 x 10-5 |/1.75 x 10-5] x 100

% Error = 60.5%

Error of Ka from pH of Half-Neutralization Point: 29.7%

% Error = [|Theoretical Ka - Experimental Ka |/Theoretical Ka] x 100

% Error = [|1.23x10-5- 1.75 x 10-5 |/1.75 x 10-5] x 100

% Error = 29.7%

Discussion: Based on the results obtained from the experiment, the equivalence volume of the titration of the weak acid (HC2H3O2) and strong base NaOH was 28.11 mL, the calculated Ka from the pH of the original solution was 6.92 x 10-6, and the calculated Ka from the pH of the Half-Neutralization point was 1.23x10-5. There was a 60.5% error in the calculated Ka from the pH of the original solution and 29.7% error in the calculated Ka from the pH of the Half-Neutralization point, indicating that there could have been numerous sources of