Tham khảo sách 'chemistry part 37, julia burdge,2e (2009)', khoa học tự nhiên, hoá học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 916 CHAPTER 24 Nonmetallic Elements and Their Compounds Figure Structures of some common phosphorus-containing oxoacids. Phosphorous acid H3PO3 Phosphoric acid H3PO4 Hypophosphorous acid H3PO2 Triphosphoric acid H5P3OJ0 Pregnant women are advised not to consume large quantities of soda because of the phosphate content. In the pure form phosphoric acid is a colorless solid . C . The phosphoric acid we use in the laboratory is usually an 82 H3PO4 solution by mass . Phosphoric acid and phosphates have many commercial applications in detergents fertilizers flame retardants and toothpastes and as buffers in carbonated beverages. Like nitrogen phosphorus is an element that is essential to life. It constitutes only about 1 percent by mass of the human body but it is a very important 1 percent. About 23 percent of the human skeleton is mineral matter. The phosphorus content of this mineral matter calcium phosphate Ca3 PO4 2 is 20 percent. Our teeth are basically Ca3 PO4 2 and Ca5 PO4 3OH. Phosphates are also important components of the genetic materials deoxyribonucleic acid DNA and ribonucleic acid RNA . Oxygen and Sulfur Oxygen Oxygen is by far the most abundant element in Earth s crust constituting about 46 percent of its mass. In addition the atmosphere contains about 21 percent molecular oxygen by volume 23 percent by mass . Like nitrogen oxygen in the free state is a diatomic molecule O2 . In the laboratory oxygen gas can be obtained by heating potassium chlorate 2KC1030 ------- 2KCl s 3O2 g The reaction is usually catalyzed by manganese IV dioxide MnO2 . Pure oxygen gas can be prepared by electrolyzing water page 781 . Industrially oxygen gas is prepared by the fractional distillation of liquefied air. Oxygen gas is colorless and odorless. Oxygen is a building block of practically all biomolecules accounting for about a fourth of the atoms in living matter. Molecular oxygen is the essential oxidant in the metabolic breakdown of food molecules. Without
