Question

Vinegar titration

Answer 1

Vinegar titration

Vinegar is essentially a solution of acetic acid (HC2H3O2) in water. The concentration of acetic acid in vinegar may be expressed as a molarity (in mol/L) or as a mass percent, where:

Molarity = Moles of Acetic Acid / Volume of Vinegar (in L)

Mass % = [Mass of Acetic Acid / Mass of Vinegar] x 100

A technique known as a titration will be used to determine the concentration of acetic acid in vinegar. A titration involves performing a controlled reaction between a solution of known concentration (the titrant) and a solution of unknown concentration (the analyte). Here, the titrant is an aqueous solution of ~ 0.1 M sodium hydroxide (NaOH) and the analyte is vinegar. When mixed, a neutralization reaction occurs between sodium hydroxide and the acetic acid in vinegar:

NaOH (aq) + HC2H3O2 (aq) ? NaC2H3O2 (aq) + H2O (l)

The sodium hydroxide will be gradually added to the vinegar in small amounts from a burette. A burette is a device that allows the precise delivery of a specific volume of a solution. The NaOH will be added to the vinegar sample until all the acetic acid in the vinegar has been exactly consumed (reacted away). At this point the reaction is completed, and no more NaOH is required. This is called the equivalence point of the titration. In order to know when the equivalence point is reached, an indicator solution called phenolphthalein is added to the vinegar at the beginning of the titration. Phenolphthalein is a pH sensitive organic dye. Phenolphthalein is colorless in acidic solutions like vinegar, and deep pink in basic solutions like sodium hydroxide. At the equivalence point of the titration, just one drop of NaOH will cause the entire solution in the Erlenmeyer flask to change from colorless to a very pale pink.

As the titration is performed, the following data will be collected: (1) the molarity of NaOH (aq) used, (2) the volume of NaOH (aq) used to neutralize the vinegar, and (3) the volume of vinegar used. Using this data, the molarity and mass percent of acetic acid in vinegar can be determined by performing a series of solution stoichiometry calculations

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