Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Citric Acid

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Citric Acid, white solid, soluble in water and slightly soluble in organic solvents, which melts at 153° C (307° F). Aqueous solutions of citric acid are slightly more acidic than solutions of acetic acid. Traces of citric acid are found in numerous plants and animals, because it is a nearly universal intermediate product of metabolism. Large amounts of the acid are found in the juice of citrus fruits, from which it is precipitated by the addition of lime; the resulting calcium citrate is treated with sulfuric acid to regenerate the citric acid. Fermentation of sugar by the mold Aspergillus niger is the chief commercial source of the acid. It is added to some foods and beverages to produce a pleasant acid flavor; it is also used in medicines, in making blueprint paper, in textile printing, and as a polishing agent for metals.