domingo, 27 de junio de 2010
Past Material of the Month
Sodium Chloride (Salt)Sodium chloride or common salt is the chemical compound NaCl. Salt occurs naturally in many parts of the world as the mineral halite and as mixed evaporites in salt lakes. Seawater has lots of salt; it contains an average of 2.6% (by weight) NaCl, or 26 million metric tons per cubic kilometer (120 million short tons per cubic mile), an inexhaustible supply (note: seawater also contains other dissolved solids; salt represents about 77% of the total dissolved solids).Salt is important in many ways. It is an essential part of the diet of both humans and animals and is a part of most animal fluids, such as blood, sweat, and tears. It aids digestion by providing chlorine for hydrochloric acid, a small but essential part of human digestive fluid. Persons with hypertensive heart disease often must restrict the amount of salt in their diet. NaCl consists of cubic close packed chloride (negative ions - yellow) with sodium (positive ions - red).Salt is widely used as a seasoning for foods and is used in curing meats and preserving fish and other foods. Iodized table salt usually contains small amounts of potassium iodide, sodium carbonate, and sodium thiosulfate. As a chemical salt is used in making glass, pottery, textile dyes, and soap. Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals. Sodium chloride is odorless but has a characteristic taste. It is an ionic compound, being made up of equal numbers of positively charged sodium and negatively charged chloride ions.