Carbonic acid, which is an aqueous solution of carbon dioxide, can interact with basic and amphoteric oxides, ammonia, and alkalis. As a result of the reaction, medium s alts are obtained - carbonates, and provided that carbonic acid is taken in excess - bicarbonates. In the article, we will get acquainted with the physical and chemical properties of magnesium bicarbonate, as well as with the features of its distribution in nature.
Qualitative reaction for bicarbonate ion
Both medium s alts and acidic ones, carbonic acid interact with acids. As a result of the reaction, carbon dioxide is released. Its presence can be detected by passing the collected gas through a solution of lime water. Turbidity is observed due to the precipitation of an insoluble precipitate of calcium carbonate. The reaction illustrates how magnesium bicarbonate, containing the ion HCO3-, reacts.
Interaction with s alts and alkalis
How do exchange reactions occur between solutions of two s alts formed by acids of different strength, for example, between barium chloride and an acid magnesium s alt? It goes with the formation of an insoluble s alt - barium carbonate. Such processes are called ion exchange reactions. They always end with the formation of a precipitate, a gas, or a slightly dissociating product, water. The reaction of an alkali of sodium hydroxide and magnesium bicarbonate leads to the formation of a medium s alt of magnesium carbonate and water. A feature of the thermal decomposition of ammonium carbonates is that, in addition to the appearance of acid s alts, gaseous ammonia is released. S alts of carbonate acid, when heated strongly, can interact with amphoteric oxides, such as zinc or aluminum oxide. The reaction proceeds with the formation of s alts - magnesium aluminates or zincates. Oxides formed by non-metallic elements are also capable of reacting with magnesium bicarbonate. New s alt, carbon dioxide and water are found in the reaction products.
Minerals widespread in the earth's crust - limestone, chalk, marble, interact with carbon dioxide dissolved in water for a long time. As a result, acidic s alts are formed - magnesium and calcium bicarbonates. When the environmental conditions change, for example, when the temperature rises, reverse reactions occur. Medium s alts, crystallizing from water with a high concentration of bicarbonates, often form icicles from carbonates - stalactites, as well as growths in the form of towers - stalagmites in limestone caves.
Water hardness
Water interacts with s alts contained in the soil, such as magnesium bicarbonate, the formula of which is Mg(HCO3)2. She dissolves them, and she becomes rigid. The more impurities, the worse the products boil in such water, their taste and nutritional value deteriorate sharply. Such water is not suitable for washing hair and washing clothes. Hard water is especially dangerous for use in steam installations, since calcium and magnesium bicarbonates dissolved in it precipitate during boiling. It forms a layer of scale that does not conduct heat well. This is fraught with such negative consequences as excessive fuel consumption, as well as overheating of boilers, leading to their wear and accidents.
Magnesium and calcium hardness
If calcium ions are present in an aqueous solution along with HCO anions3-, then they cause calcium hardness, if magnesium cations - magnesium. Their concentration in water is called total hardness. With prolonged boiling, bicarbonates turn into poorly soluble carbonates, which precipitate as a precipitate. At the same time, the total hardness of water is reduced by an indicator of carbonate or temporary hardness. Calcium cations form carbonates - medium s alts, and magnesium ions are part of magnesium hydroxide or basic s alt - magnesium carbonate hydroxide. Especially, high rigidity is inherent in the water of the seas and oceans. For example, in the Black Sea, magnesium hardness is 53.5 mg-eq / l, and in the Pacificocean – 108 mg-eq/l. Along with limestone, magnesite is often found in the earth's crust - a mineral containing carbonate and bicarbonate of sodium and magnesium.
Water softening methods
Before using water, the total hardness of which exceeds 7 mg-eq / l, it should be freed from excess s alts - softened. For example, calcium hydroxide, slaked lime, can be added to it. If soda is added at the same time, then you can get rid of constant (non-carbonate) hardness. More convenient methods are also used that do not require heating and contact with an aggressive substance - alkali Ca(OH)2. These include the use of cation exchangers.
The principle of operation of the cation exchanger
Aluminosilicates and synthetic ion exchange resins are cation exchangers. They contain mobile sodium ions. Passing water through filters with a layer on which the carrier is located - a cation exchanger, sodium particles will change into calcium and magnesium cations. The latter are bound by the anions of the cation exchanger and are firmly held in it. If there is a concentration of Ca2+ and Mg2+ ions in water, then it will be hard. To restore the activity of the ion exchanger, the substances are placed in a solution of sodium chloride, and the reverse reaction occurs - sodium ions replace the magnesium and calcium cations adsorbed on the cation exchanger. Refurbished ion exchanger ready for hard water softening process again.
Electrolytic dissociation
Most of the medium and acid s alts inin aqueous solutions, it splits into ions, being a conductor of the second kind. That is, the substance undergoes electrolytic dissociation and its solution is able to conduct an electric current. The dissociation of magnesium bicarbonate leads to the presence of magnesium cations and negatively charged complex ions of the carbonic acid residue in the solution. Their directed movement to oppositely charged electrodes causes the appearance of an electric current.
Hydrolysis
The exchange reactions between s alts and water, leading to the appearance of a weak electrolyte, is hydrolysis. It is of great importance not only in inorganic nature, but also is the basis for the metabolism of proteins, carbohydrates and fats in living organisms. Bicarbonate of potassium, magnesium, sodium and other active metals, formed by a weak carbonic acid and a strong base, is completely hydrolyzed in an aqueous solution. When colorless phenolphthalein is added to it, the indicator turns crimson. This indicates the alkaline nature of the environment, due to the accumulation of excess concentration of hydroxide ions.
Purple litmus in an aqueous solution of an acid s alt of carbonic acid turns blue. An excess of hydroxyl particles in this solution can also be detected using another indicator - methyl orange, which changes its color to yellow.
The cycle of s alts of carbonic acid in nature
The ability of bicarbonates to dissolve in water underlies their constant movement in inanimate and living nature. Groundwater, saturated with carbon dioxide, seeps through the layers of soil, intocomposed of magnesite and limestone. Water with bicarbonate and magnesium enters the soil solution, then is carried out into rivers and seas. From there, acidic s alts enter the organisms of animals and go to the construction of their external (shells, chitin) or internal skeleton. In some cases, under the influence of the high temperature of geyser or s alt springs, hydrocarbonates decompose, releasing carbon dioxide and turning into mineral deposits: chalk, limestone, marble.
In the article, we studied the features of the physical and chemical properties of magnesium bicarbonate and found out the ways of its formation in nature.
