15.2 Important compounds of alkaline earth metals. Carbonates.

15.2 Important compounds of alkaline earth metals. Carbonates. you will:10.2.1.12 ???????? ??????? ?????????? ????????? ?????????? ???????????????? ????????; 10.2.1.14 ?????????? ????? ??????????? ?????????? ? ??????? ? ???????? ??????? ?? ??????????; OccurrenceSince the Group 2 elements are relatively active metals, they occur in compounds in nature. Beryllium occurs in trace amount in nature. The most important ores of beryllium is beryl, alexandrite, lazurite, emerald, Be3Al2(SiO3)6Alexandrite 109026980 Lazurite 719638693Emerald   635405621The principal useful ores of magnesium are magnesite MgCO3, dolomite CaCO3×MgCO3(a double salt), asbestos Mg3Si2O7×2H2O, carnallite KCl×MgCl2×6H2O and Epsom salt MgSO4×7H2O which is found in mineral water. Epsom salts are used as a purgative, as a dressing for cotton goods and in dye. Asbestos roofs   292690871Magnesite mineral  689648494Calcium compounds are widely distributed in nature, occurring as limestone or marble CaCO3, gypsum CaSO4×2H2O, apatite  and fluorite CaF2. Salts of sulfate, silicate and phosphate are also found in the Earth’s crust. Purple apatite (calcium phosphate) mineral  723025126 Gypsum statue 748413898Strontium, barium, radium are found in trace amount in nature. Strontium occurs as celestite (SrSO4) and strontianite (SrCO3), barium occurs as barytes (BaSO4) and witherite (BaCO3). All the isotopes of radium are radioactive. The isotope 226Ra is the most stable isotope with a 1600 year half life. The radium element is a side product of the natural decay of 238U.    Radium was isolated in its metallic state by Marie and Pierre Curie  339956723  Baryte mineral  599760158The compounds of alkaline earth metals are ionic. They have high melting and boiling points. They are thermally stable. Their salts are less soluble in water than those of alkali metals. And the solubilities of salts increase from beryllium to barium. Most of the compounds of beryllium and some compounds of magnesium show a tendency to covalency, so they differ from other compounds in the group. General characteristics of compounds of the alkaline earth metalsOxides and hydroxides. The alkaline earth metals burn in oxygen to form the monoxide, MO which, except for BeO, have rock-salt structure. All these oxides except BeO are basic in nature and react with water to form sparingly soluble hydroxides. The solubility, thermal stability and the basic character of these hydroxides increase with increasing atomic number from Mg(OH)2 to Ba(OH)2.Halides.Except for beryllium halides, all other halides of alkaline earth metals are ionic in nature. Beryllium halides are essentially covalent and soluble in organic solvents. The tendency to form halide hydrates gradually decreases (for example,MgCl2×8H2O, CaCl2×6H2O, SrCl2×6H2O and BaCl2×2H2O) down the group. The fluorides are relatively less soluble than the chlorides owing to their high lattice energies.CarbonatesCarbonates of alkaline earth metals are insoluble in water and can be precipitated by addition of a sodium or ammonium carbonate solution to a solution of a soluble salt of these metals. The solubilityof carbonates in water decreases as the atomic number of the metal ion increases. All the carbonates decompose on heating to give carbon dioxide and the oxide. Beryllium carbonate is unstable and can be kept only in the atmosphere of CO2.SulfatesThe sulphates of the alkaline earth metals are all white solids and stable to heat. BeSO4, and MgSO4are readily soluble in water; the solubility decreases from CaSO4 to BaSO4.The greater hydration  enthalpies of Be2+ and Mg2+ ions overcome the lattice enthalpy factor and therefore their sulfates are soluble in water.NitratesThe nitrates are made by dissolution of the carbonates in dilute nitric acid. Magnesium nitrate crystallises with six molecules of water, whereas barium nitrate crystallises as the anhydrous salt. This again shows a decreasing tendency to form hydrates with increasing size and decreasing hydrationenthalpy. All of them decompose on heating to give the oxide like lithium nitrate: 2Me(NO3)2 ? 2MeO + 4NO2 + O2          Some important compounds of calcium Important compounds of calcium are calcium oxide, calcium hydroxide, calcium sulphate, calcium carbonate and cement. These are industrially important compounds.Calcium oxide (lime) is used in the production of cement, and is obtained by heating calcium carbonate (limestone) at 900°C. CaCO3 ? CaO + CO2Addition of calcium oxide to water is called slaking, and the product, Ca(OH)2, is called slaked lime (lime water). CaO + H2O  ? Ca(OH)2Ca(OH)2 is used in the preparation of mortar (slaked lime plus sand) which sets to a solid by reconversion of the Ca(OH)2 to CaCO3 as a result of the reaction with CO2 in air. Ca(OH)2(s) + CO2(g)  ? CaCO3(s) + H2O(g)Calcium carbonate occurs naturally as marble, limestone, chalk and calcite. As mentioned above, it forms by evolving CO2 gas from Ca(OH)2 solution. Underground water containing CO2 dissolve some amount of CaCO3 and the equilibrium below is established. CaCO3(s) + CO2(g) + H2O(l) ? Ca(HCO3)2(aq)When such underground water reaches the earth’s surface, the pressure on it decreases. Because of the decrease in solubility of CO2 in water, the equilibrium reaction shifts to the left, that is, CaCO3 precipitate is formed. Formation of stalactites and stalagmites is a good example of this process.Calcium carbonate (CaCO3) is used as a blackboard chalk, in the purification of iron from iron ore in a blast furnace, in the oil industry in drilling fluids,  in swimming pools as a pH corrector for maintaining alkalinity “buffer” to offset the acidic properties of the disinfectant agent. Stalactites and stalagmites in a cave   169068131In nature, its anhydrate CaSO4 and dihydrate forms CaSO4×2H2O are called gypsum and alabaster. Gypsum CaSO4×2H2O is a white substance which is used commercially for fabrication into wallboard. When gypsum is heated above 100°C, it loses 3/4 of its water of crystallization, forming the powdered substance CaSO4×0.5H2O, known as plaster of Paris.2CaSO4×2H2O ? 2CaSO4×0.5H2O + 3H2OBy mixing with water, the small crystals of plaster of Paris dissolve and then re-crystallize as long needles of CaSO4×2H2O. Calcium sulfate, CaSO4 is a constituent of cement. Additionally, it is used in decoration as plaster of Paris, and in dentistry to mold teeth.Gypsum has been used indrywallplaster ingredientfertilizer and soil conditionersurgical splints, casting molds, modelingadding hardness to water used for homebrewing.a component of Portland cement used to prevent flash setting of concrete.Kazakhstan is rich in natural resources, and mining is quite important to the economy of Kazakhstan. Among the best-known deposits of phosphates are the Karatau Range, Mangystau and Aktobe region. The Zhambyl region belt is the gypsum producing area in the country. The Kostanay region is rich in minerals dolomite and asbestos in Zhitikara. Karatau Ridge    743063965 Biological role of magnesium and calciumAn adult body contains about 25 g of Mg and 1200 g of Ca compared with only 5 g of iron and 0.06 g of copper. The daily requirement in the human body has been estimated to be 200 – 300 mg.All enzymes that utilise ATP in phosphate transfer require magnesium as the cofactor. The main pigment for the absorption of light in plants is chlorophyll which contains magnesium. About 99 % of body calcium is present in bones and teeth. It also plays important roles in neuromuscular function,interneuronal transmission, cell membrane integrity and blood coagulation.??? ??????? ???? ????? ??? ????? wwwwwdfe