Determination of Acetic Acid in Vinegar Using a Ph Electrode

Determination of Acetic Acid in Vinegar using a pH Electrode

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Background

What is vinegar?

Vinegar principally consists of acetic acid and water.  Because of its chemical properties, vinegar can be used in a variety of ways: as a cleanser, salad dressing, disinfectant, preservative, or cooking ingredient.  As such, it is a very common household item. 

Vinegar is produced from fermentation of sugars. Fermentation processes have been used for food preservation since ancient times. Fermentation is a chemical change produced in organic substances by the action of enzymes. Fermentation can produce lactic acid, as in fermentation of milk to yogurt; or alcohol or acetic acid, as in fermentation of fruit. As Ben Selinger explains in Chemistry in the Marketplace, "Fermentation of food to produce acid is common to all cultures and cuisines, e.g., pickles, sauerkraut, coffee beans, kimchi, salami, cheese, sour dough bread, soy sauce."  Bacteria, yeasts, and molds are used to produce lactic acid or acetic acid or both. Fermentation to alcohol produces a pleasant, but not stable, product unless the concentration of alcohol is fairly high. Thus, wine turns to vinegar over time.

Fermentation also can happen in human intestines when certain bacteria are present that work on undigested carbohydrates. The troublesome products are gases such as carbon dioxide or hydrogen sulfide that may be formed in quantities sufficient to cause distention and pain.

The starting materials to vinegar production can be any fruit or source of sugars. They are fermented with yeast to convert the sugar to ethanol (CH3CH2OH). The ethanol is then oxidized (oxygen added) to form acetic acid (CH3COOH) by bacterial digestion of the ethanol. Check the following link:

http://www.bioteach.ubc.ca/Bioengineering/beerandwine/index.htm

A strong acid is an acid that completely ionizes in aqueous solutions.  For example, the hydrochloric acid solution that you used for a recent Chem 184 lab is a strong...