Theory of Determination of the Concentration of Acetic Acid in Vinegar

THEORY

In the titration process, a burette is used to dispense a small, quantifiable increment of solution of known concentration. A typical burette has the small calibration unit 0.1mL, therefore the volume dispensed from the burette should be estimated to the nearest 0.05mL.

In this experiment, the equivalence point occurs when the moles of acid in the solution equals to the moles of base added in the titration. For example, the stoichiometric amount of 1 mole of the strong base, sodium hydroxide (NaOH), is necessary to neutralize 1 mole of the weak acid, acetic acid (CH_3 COOH), as indicated in:

NaOH_((aq))+CH_3 CO_2 H_((aq))→NaCH_3 CO_(2(aq))+H_2 O_((l))

base + acid  salt + water

The sudden change in the solution pH shows that the titration has reached the equivalence point. pH in the aqueous solution is related to its hydrogen ion concentration is written as [H_3 O^+]. pH is defined as the negative of the logarithm of the hydrogen ion concentration.

pH=-log_10 [H_3 O^+]

pH scale is a method of expressing the acidity or basicity of a solution. Solution with pH 7 are basic. For example, a solution having an H_3 O^+ concentration of 2.34×10^(-2)M would have a pH of 1.629 and is acidic. pH electrodes will be used in this experiment. The titration is initiated by insrting a pH electrode into a beaker containing the acid solution (pH within 3-5). As sodium hydroxide (NaOH) is a incrementally added to the acid solution, some of the hydrogen ions will be neutralized, as the hydrogen ion concentration decreases, the pH of the solution wil gradually increase. When sufficient NaOH is added to completely neutralize the acid will cause a sudden sharp increase in pH the volume of based required to completely neutralized the acid is determined at the equivalence point of titration.

In this experiment, titration of a vinegar sample with a standardized sodium hydroxide solution will be performed. To standardize the sodium hydroxide solution, a primary...