Titration

Titration is a technique that can be used to determine the amount of substance present in a solution. For instance, we can estimate the amount of acetic acid present in a vinegar sample by titrating the sample with standard sodium hydroxide solution. Determining the percent of acetic acid in a sample is one way in which commercial vinegar samples are evaluated. Once we determine the percent acetic acid and the cost of the vinegar per ounce, we can then calculate the relative cost of the acetic acid content. Solution of the unknown concentration is known as analyte whereas solution of the known concentration is known as titrant. Analyte + Titrant → Product. Equivalent point is the point at which the right volume of titrant has been added to complete the reaction.

Cabbage juice, which has a light purple coloration can act as an indicator. It forms a red color in a strongly acidic solution. It will form a pink color in a slightly acidic solution. In pure water, cabbage juice will become light purple. However, in a strongly basic/alkaline solution, cabbage juice will turn into a deep green color. The intensity of the color varies with the strength of the base, thereby, cabbage juice will form a light green color in a slightly basic/alkaline solution. Phenolphthalein is also another indicator that remains colorless in acidic solution and turns faint pink in a basic solution.

Titrating the acetic acid in 25.00 mL of the sample with a solution of NaOH of known normality will enable us to carry out the analysis of vinegar according to the following equation:

CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H20(l)

We can use the following equation to determine the number of gram equivalents of acetic acid in the portion of the sample titrated.

# of gram-equivalents of acetic acid in 25.00 ml= (NNaOH)(VNaOH)

Number of grams of acetic acid in 25.00 mL = (# of gram-equivalents in 25.00 ml)( gram-equivalent weight of acetic acid)

Making assumptions that the density of the vinegar sample to be 1.00 g/mL , the percent by mass of acetic acid in the vinegar sample can be found using the following equation:

Percent acetic acid = (mass of acetic acid, g/mass of vinegar sample, g)(100)

The purpose of this experiment is to determine the percent acetic acid