Citric acid is a weak, naturally occurring acid from citrus fruits. It has natural preservative properties and is used to give foods, candies and sodas a mouth-puckering sour taste. Like all chemical compounds, citric acid has specific properties.
Citric acid's mild acidity is the result of three carboxyl groups (three compounds made up of a carbon atom bound with two oxygen and one hydrogen atoms). If these groups of compounds lose a proton when mixed with a solvent, this results in the creation of an ion of citrate. Citrates act as buffers for controlling the pH balance of acidic solutions.
Citric Acid Citrates
When ions of citrate combine with metal ions, they form salts called citrates. One of the most widely used is calcium citrate, also known as "sour salt." Sour salt is often used to preserve foods. It also is commonly used in popular sour candies. Citrates have the ability to chelate, or bond with, metal ions, which lends them to be used as water-softening agents in laundry detergents.
Citric acid is a white crystalline powder when it is at room temperature. Citric acid powder can exist in one of two forms: anhydrous (water-free) or monohydrate (one molecule of water is bound to each molecule of citric acid). Anhydrous citric acid crystallizes from hot water. Monohydrate citric acid crystallizes in cold water.