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, middle salts are obtained - carbonates, and provided that carbonate acid is taken in excess - hydrocarbonates. 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 to bicarbonate ion
Both middle salts and acidic, carbonic acids 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 an HCO 3 - ion reacts.
Interaction with salts and alkalis
How do exchange reactions occur between solutions of two salts formed by acids of different strengths, for example, between barium chloride and magnesium acid salt? It goes with the formation of an insoluble salt - barium carbonate. Such processes are called ion exchange reactions. They always end with the formation of a precipitate, gas or a little dissociative product - water. The alkali reaction of sodium hydroxide and magnesium bicarbonate leads to the formation of a medium salt of magnesium carbonate and water. A feature of the thermal decomposition of ammonium carbonates is that, in addition to the appearance of acid salts, gaseous ammonia is released. Salts of carbonate acid with strong heating can interact with amphoteric oxides, such as zinc or aluminum oxide. The reaction proceeds with the formation of salts - aluminates or magnesium zincates. Oxides formed by non-metallic elements are also able to react with magnesium bicarbonate. In the reaction products, a new salt, carbon dioxide and water are found.
The minerals widely distributed in the earth's crust - limestone, chalk, marble, for a long time interact with carbon dioxide dissolved in water. As a result, acid salts are formed - magnesium and calcium bicarbonates. When environmental conditions change, for example, when the temperature rises, reverse reactions occur. Medium salts, crystallizing from water with a high concentration of bicarbonates, often form icicles of carbonates - stalactites, and also growths in the form of towers - stalagmites in calcareous caves.
Hardness of water
Water interacts with salts contained in the soil, for example, magnesium bicarbonate, the formula of which is Mg (HCO 3 ) 2 . She dissolves them, and she becomes tough. The more impurities, the worse the products are digested in such water, their taste and nutritional value sharply worsen. Such water is not suitable for washing hair and washing clothes. Hard water is especially dangerous for use in steam plants, since during boiling, the calcium and magnesium bicarbonates dissolved in it precipitate. It forms a scale layer that does not conduct heat well. This is fraught with negative consequences such as excessive consumption of fuel, as well as overheating of the boilers, leading to their wear and tear and accidents.
Magnesium and calcium hardness
If calcium ions are present in the aqueous solution along with HCO 3 - anions, then they determine calcium hardness, while magnesium cations are magnesium. Their concentration in water is called general hardness. With prolonged boiling, bicarbonates turn into poorly soluble carbonates, which precipitate in the form of a precipitate. In this case, the total hardness of water decreases by an indicator of carbonate or temporary hardness. Calcium cations form carbonates - medium salts, and magnesium ions are part of magnesium hydroxide or the main salt - 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 mEq / L, and in the Pacific Ocean it is 108 mEq / L. Along with limestone, magnesite is often found in the earth's crust - a mineral containing sodium and magnesium carbonate and hydrogen carbonate.
Water softening methods
Before using water, the total hardness of which exceeds 7 mEq / l, it should be freed from excess salts - softened. For example, you can add calcium hydroxide - slaked lime. If you add soda at the same time with it, then you can get rid of constant (non-carbonate) stiffness. Apply more convenient methods 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 action of cation exchanger
Aluminosilicates and synthetic ion-exchange resins are cation exchangers. They contain in their composition mobile sodium ions. By passing water through filters with a layer on which the carrier is located - cation exchange resin, sodium particles will change to calcium and magnesium cations. The latter are bound by cation exchange resin anions and are firmly held in it. If the concentration of Ca 2+ and Mg 2+ ions is present in water, then it will be stiff. To restore the activity of the ion exchanger, the substances are placed in a solution of sodium chloride, while the opposite reaction occurs - sodium ions replace the cations of magnesium and calcium adsorbed on cation exchange resin. The recovered ion exchanger is again ready for the process of softening hard water.
Electrolytic dissociation
Most of the medium and acid salts in aqueous solutions are split 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. 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 towards oppositely charged electrodes also causes the appearance of an electric current.
Hydrolysis
The exchange reaction between salts 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 of the processes of protein, carbohydrate and fat metabolism in living organisms. Bicarbonate of potassium, magnesium, sodium and other active metals, formed by 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 medium, due to the accumulation of an excessive concentration of hydroxide ions.
Purple litmus in an aqueous solution of an acidic salt of carbonic acid turns blue. An excess of hydroxyl particles in this solution can also be detected with the help of another indicator - methyl orange, which changes its color to yellow.
The cycle of carbonic salts 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 soil layers, which include magnesite and limestone. Water with bicarbonate and magnesium gets into the soil solution, then it is carried out into rivers and seas. From there, acid salts enter animal organisms and go to build their external (shell, chitin) or internal skeleton. In some cases, under the influence of high temperature of geyser or salt sources, bicarbonates 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.