Calcium and magnesium compounds
So, having determined yesterday how much calcium is contained in the crushed eggshell, the question arose “to drink or not to drink?”. Like most men, I come up with everything from a scientific point of view and until I see it myself, find out, check, feel a word for a woman. Therefore, I will share my thoughts on the basis of the information found about eggshell and calcium.
Collecting on the Internet information about the use of egg shell as a food additive more than once came across the critical remarks of doctors that calcium carbonate contained in the egg shell is insoluble in water and therefore can not be absorbed by the body.
Moreover, the story of my friend's spouse was recalled that during pregnancy she told her doctor, who had observed that she was taking crushed egg shells - the doctor dissuaded her and prescribed some kind of calcium-containing complex.
Where is the truth?
Indeed, calcium carbonate ССО3 (precisely in this type, calcium is in the egg shell) is insoluble in water and alcohol.
A really necessary precondition for calcium absorption is its water solubility.
But remember that the basis of our digestion is hydrochloric acid excreted in the stomach.
And that's what happens in our stomach:
СaCO3 + 2HCl (hydrochloric acid) = СaCl2 (calcium chloride) + Co2 + H20
But calcium chloride is perfectly soluble in water !!! It is in this form that calcium is absorbed!
Do not know the doctors? Or they are simply cunning and sell us medicines!
Plus, during this reaction, a decrease in gastric acidity occurs. What is important for people suffering from high acidity.
An example is my wife, she has high acidity, and she takes a little crushed eggshell every day and this solves two problems at once and compensates for the lack of calcium and lowers her acidity. But the egg shell powder extinguished lemon juice can not drink - there is nausea! And now I understand why.
As we saw above, for the absorption of calcium from calcium carbonate requires gastric juice with high acidity.
In real life, very often a situation occurs when the acidity of the stomach is low or zero. This situation is especially characteristic of older people, when the need for calcium is especially high to prevent osteoporosis. For example, after 50 years, low acidity occurs in about 40% of people. Under these conditions, the absorption of calcium carbonate, which requires hydrochloric acid to dissolve in the stomach, drops to 2%.
Perhaps this is the answer why older people are more likely to suffer from diseases associated with a lack of calcium - they just can not assimilate it in its usual form.
Now consider why many recipes for receiving crushed eggshell are advised to quench it with lemon juice.
When we add lemon juice to crushed citric acid, calcium carbonate (CaCo3) reacts with citric acid (C6H8O7) and we get calcium citrate (Ca3 (C6H5O7) 2):
2C6H8O7 + 3CaCO3 = Ca3 (C6H5O7) 2 + 3CO2 + 3H2O
Here it is. And the absorption of calcium citrate, which does not require hydrochloric acid in the stomach, is 44%. As a result, under conditions of low acidity, calcium citrate enters the body in 11 times more calcium than from carbonate!
And calcium citrate is already a well-known medicine that is sold to us for money! And they do it, only they use not lemon juice, but citric acid!
By the way, calcium carbonate (our shredded eggshell) is a registered food additive. E170, and calcium citrate (our shredded eggshell poured with lemon juice) is a registered food additive. E333! And they are added to many food products, especially dairy products, including milk, to increase the percentage of calcium !.
So why pay more!
Conclusion, if you have high acidity - it is probably better to use just shredded egg shells, if the acidity is lower, it is probably better to extinguish the egg shell powder with lemon juice.
And further,
At night, there is an accelerated release of mineral salts from the body (circadian acceleration of resorptive processes in the bone). Therefore, calcium preparations should be taken after lunch and in the evening.That will prevent the accelerated loss of calcium in the second half of the night, especially with its reduced level (or absence) in the intestine. The negative dose-dependent effect of the pharmacotherapeutic activity of calcium is also noted: in low doses this biometall is absorbed better than in high.
Concerning more rational to take the drug several times a day.
We read, we discuss. Below are a few articles on this topic.
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Calcium citrate versus calcium carbonate
A source< http://www.ortho.ru/77_KMD/Ca_Sravni.htm >
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Calcium citrate.
Calcium citrate is an excellent source of absorbed calcium, which plays a very important role in the body, because it affects many enzymatic processes and blood clotting. Calcium deficiency leads to bone fragility and osteoporosis. For young children, it is good for dental health; adults need regular calcium intake to stabilize blood pressure.
According to the National Cancer Institute (USA), E-333 supplement can potentially prevent colon cancer and other cancers. In addition, calcium citrates are used in medicine to remove heavy metals from the body.
Since calcium citrate is one of the most important transport forms of calcium in the human body, it is used in medicine along with less effective calcium carbonate (E-170 additive) to replenish calcium reserves in the body. For the same reason, calcium citrate is used in the form of dietary supplements (dietary supplements).
In the food industry, E-333 additive is used as a stabilizer, preservative, acidity regulator, color fixative.
As a stabilizer, the food additive E-333 is used in the manufacture of condensed milk, cream, cream cheese. In jams, jelly and canned fruit, E-333 additive is used as an acidity regulator. Calcium citrates are also widely used to enrich calcium in milk and dairy products, bakery and flour products, and soft drinks.
In appearance, calcium citrate is a white powder with a pronounced sour taste. Soluble in water. Molecular formula of calcium citrate: Ca3 (C6H5O7) 2. Get E-333 by the interaction of citric acid with calcium hydroxide.
Properties and technological functions:
Possible names of food supplements:
- E-333
- E-333
- Calcium citrate
- Calcium citrates
- Monocalcium citrate
- Dicalcium citrate
- Tricalcium citrate
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Calcium Citrate
In the middle of the twentieth century. a kind of “boom” began: biochemists, physiologists, biophysicists, pharmacologists and clinicians began to show an increased interest in studying the role of calcium in regulating the activity of organs and body systems. Calcium ions have been found to be involved in the excitation and contraction of muscle cells, regulation of cell membrane permeability, intercellular interactions, blood coagulation, hormone secretion, mediators, enzymes; perform the function of a signal transducer entering the cell, participate in the processes of regulation of intracellular metabolism, including energy. On the surface of the membrane of cardiomyocytes and vessels of free calcium ions is 1000 times more than in the cytosol of cells. From the extracellular space they penetrate into the cytoplasm through special calcium channels, affecting various physiological processes and functions of cells of all organs, vascular tone, intensity of systole, diastole.
Calcium plays an important role in the formation of bone tissue and the preservation of its normal structure and function. Along with special proteins, calcium ions provide bone hardness and elasticity.
All this served as a theoretical foundation for the development and introduction of calcium preparations based on its salts into medical practice. Currently, in the medical practice, such calcium salts as glycerophosphate, gluconate, carbonate, lactate, citrate, chloride, phosphate and many others are used.
The pharmacokinetics of the drug CALCIUM CITRATE has its own characteristics. Calcium is absorbed from the intestine in a soluble, ionized form. The dissolution of the drug occurs better in the acidic environment of the stomach. Dissolved ionized calcium penetrates well into all tissues, penetrates the placental barrier, passes into breast milk. Excreted mainly in the feces, about 20% - with the urine. An important feature of Calcium Citrate is the low ability to form kidney stones, which is important with long-term use of this salt. This is due to the fact that citrate salt reduces the amount of oxalate in the urine.
Bioavailability is determined by the speed and extent to which active substance absorbed from the dosage form, it becomes available at the site of the intended therapeutic action.
At night, there is an accelerated release of mineral salts from the body (circadian acceleration of resorptive processes in the bone). Therefore, calcium preparations should be taken after lunch and in the evening, which will prevent the accelerated loss of calcium in the second half of the night, especially with its reduced level (or absence) in the intestine. The negative dose-dependent effect of the pharmacotherapeutic activity of calcium is noted: this biometal is absorbed better at low doses than at high doses. In this regard, it is more rational to take the drug several times a day. For different age groups there are different physiological norms of calcium intake (table).
Table
The recommended rate of calcium intake in people of different ages
(according to the Canadian Society for Osteoporosis)
Vitamin D, hydrochloric acid, lactose, citric acid, the presence of protein in food, phosphorus, magnesium, as well as some foods such as butter, eggs, milk, fish, cod fat, cabbage, etc., contribute to the absorption of calcium ions.
Calcium absorption is worsening: lack of protein in food, strict observance of a vegetarian diet, lack of magnesium, phosphorus, foods rich in oxalic acid (sorrel, rhubarb, spinach).
Calcium absorption slows down in diseases of the digestive organs (gastritis, enteritis, colitis, peptic ulcer), pancreas (diabetes, pancreatitis), pathologies of other endocrine organs.
It should be emphasized that some drugs, especially glucocorticoids, hormonal contraceptive drugs for systemic use, levothyroxine also worsen the absorption of calcium ions.
According to the results of scientific research (data of the Canadian Society for Osteoporosis), there is no convincing evidence on the basis of which additional consumption of other minerals (magnesium, zinc, copper, etc.) can be recommended for the prevention or treatment of osteoporosis.
The results of clinical studies conducted in Ukraine and other countries have confirmed the high effectiveness of this drug in the treatment of many diseases. Calcium citrate is also used for prophylactic purposes in various diseases.
With osteoporosis in elderly people, osteomalacia CALCIUM CITRATE is prescribed 2-6 tablets per day, dividing the daily dose into 3-4 doses. The drug is taken before meals or 1–1.5 hours after a meal, for 3 months. Such patients should also be prescribed vitamin D3 of 400–800 IU per day, and also include oil, milk, fish, and eggs in the diet.
CALCIUM CITRATE is the optimal dosage form for providing calcium not only for adults, but also for children, as well as adolescents, as it helps to increase bone mineral density, increase bone mass, strengthen dentin and tooth enamel. Children under the age of 6 months are prescribed 1/2 tablets (250 mg) (crushed, dissolved in a small amount of milk), at the age of 6–12 months - also 1/2 tablets 2 times a day, at the age of 1 year – 10 years - 1-2 tablets, 10-18 years old - 2-3 tablets per day.
Indications for appointment Calcium Citrate are:
hypocalcemia due to bleeding of various origin, as well as during pregnancy and lactation, with injuries - to fill the increased body's need for calcium ions;
violation of calcium absorption in diseases of the digestive tract and an increased level of calcium excretion through the kidneys and intestines;
hypoparathyroidism, dehydration of an organism of various genesis, allergic diseases and allergic complications while taking medications, increased vascular wall permeability, reduced blood clotting.
CALCIUM CITRATE must be prescribed when taking glucocorticoids, oral contraceptives, levothyroxine. In the last three cases, the drug is taken 1 tablet 6 times a day after meals.
Calcium citrate, as a rule, is well tolerated, sometimes dyspeptic symptoms (constipation or diarrhea, nausea, vomiting, loss of appetite, abdominal pain), polyuria can occur.
The simultaneous use of CALCIUM CITRATE with antacids containing aluminum is not recommended due to a decrease in their effectiveness. It is undesirable to prescribe it simultaneously with other calcium preparations.
In conclusion, we can note the positive pharmacological properties of CALCIUM CITRATE:
citrate calcium salt is well dissolved and absorbed in the digestive tract, which leads to good absorption of calcium in the body and, accordingly, the effectiveness of the drug in its prophylactic or therapeutic applicationthat is confirmed by the results of many clinical studies.
The low risk of stone formation in the kidneys when taking the drug increases the value of calcium sulfate with prolonged use.
I.S. Chekman, Head of the Department of Pharmacology with the course of Clinical Pharmacology of the National Medical University, Corresponding Member of the National Academy of Sciences and the Academy of Medical Sciences of Ukraine, Honored Worker of Science and Technology, Professor
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The reaction of carbonates with acids can be used as a sample for carbonates. Carbonic acid is a very weak and unstable acid. It can be squeezed out of its salts by the action of less volatile and stronger acids.
Similarly, the reactions of calcium carbonate with acids proceed.
As a result of the reaction of carbonate with hydrochloric acid, calcium chloride and magnesium are obtained, which dissolve well in water and remain in the form of a solution of different concentrations. The rate of reaction in collectors of this type depends mainly on pressure and temperature.
As a result of the reaction of carbonate with hydrochloric acid calcium chloride and magnesium, well soluble in water and remaining in the form of a solution of different concentrations.
Introduction to the reaction of undried sodium carbonate causes the need to apply a higher pressure and increase the amount of catalyst.
Explanation of the phenomena listed or observed: why the reaction of calcium carbonate with sulfuric acid begins at first violently and then stops. Why when heated dry ammonium carbonate substance disappears from the tube.
The beneficial effect of calcium carbonate on the stability of Portland cement can be explained by the reaction of carbonate with aluminum-containing clinker minerals. Thus, the aluminate component of the cement stone is chemically bound before it comes into contact with the sulfates of the environment.
Some applications of barium carbonate are based on the practical insolubility of barium sulfate, which is formed by the reaction of barium carbonate with substances containing sulfate ions. So, when drying a brick before burning, white bloom appears on its surface, caused by the crystallization of gypsum or magnesium sulfate contained in the clay. To prevent this from happening, barium carbonate is added to the clay, which causes precipitation of the sulfate ion.
In his introduction to the chemistry of solids, Hedwal, as an example of a theoretically possible reaction, results in the reaction of calcium carbonate with SiO2, which results in the formation of calcium silicate. He accompanies this example by noting that with so-called geothermal metamorphoses, the usual temperature is not enough, since the reaction between calcium carbonate and silicic acid can be observed in laboratory conditions only at temperatures of 500 C.
To reduce the cost of phlegm formation in this process, Klima and Ward suggested using ammonium carbonate solution (instead of ammonium nitrate) and creating phlegm by reacting rich ammonium carbonate with lime.
As the temperature rises, the reaction shifts towards the formation of a more alkaline silicate. Gibson and Ward11 on the reaction of sodium carbonate with quartz at a temperature of from 726 to 805 C in a stream of nitrogen showed that ortho-silicate is formed in the presence of a sufficient amount of sodium carbonate. The reaction rate depends on the time, the size of the sample, the gas flow rate and the composition of the reaction mixture. Gibson and Ward argue that there are intermediate-grade sodium silicates.
Excess sodium carbonate is titrated with hydrochloric acid. The amount of sulfur in the analyzed product is calculated by the amount of sodium carbonate reacted.
And calcium carbonate and how these chemical compounds interact.
Calcium carbonate
CaCO₃ calcium carbonate latticeCaCO₃ is a very common compound in the world around; it consists of: chalk, limestone, marble, etc. Therefore, it is worth noting that the role of this substance for humans is very significant, because calcium carbonate is widely used in the food industry, as a natural white dye. CaCO₃ is also used in the manufacture of paper, plastics, in construction and in many other areas.
Calcium carbonate is a white substance (solid crystals) in powder or solid form. He is able to react with water, but not completely dissolved in it. Therefore, the water becomes turbid, and there is a white precipitate in it. But if the reaction with water will take place in the presence, then we will get a soluble acid salt, calcium bicarbonate:
CaCO₃ + CO₂ + H₂O → Ca (HCO₃)
Consider how calcium carbonate is made.
Most of the calcium carbonate is obtained from natural sources. So, to get calcium carbonate for, as a rule, use a clean source, often marble.
The marble statue of David by Michelangelo Buonarroti
But in laboratory conditions, calcium carbonate can be obtained by calcining calcium oxide. Calcination refers to the generalized notion of burning, as a result of which chemicals acquire new properties. The firing is carried out at a sufficiently high temperature, not reaching melting.
Water is mixed with the resulting calcium oxide, the reaction produces hydroxide. Then the technicians get carbon dioxide, which is passed through the previously obtained solution. The precipitate formed is calcium carbonate:
CaO + H₂O = Ca (OH);
Ca (OH) + CO₂ = CaCO₃ + H₂O
If we heat the salt of carbonic acid and calcium to a high temperature (900 - 1000 ° C), then as a result of the chemical process we will get carbon dioxide (carbon dioxide), as well as calcium oxide CaO - quicklime used in construction:
CaCO₃ = CaO + CO₂
If the temperature is even higher (1500 ° C), then the reaction products will be calcium carbide and carbon monoxide.
Hydrochloric acid
Hydrochloric acid molecule
HCl is a strong monobasic acid, which is obtained by dissolving hydrogen chloride in water. It is a colorless liquid, although the technical acid may have a yellow tint, for example, due to the impurity of iron. The properties of HCl will directly depend on the concentration of hydrogen chloride in the solution.
Salts of hydrochloric acid are called chlorides. This substance is very caustic, therefore, requires careful handling: even if a small drop falls on the skin, then a strong chemical burn can not be avoided. Therefore, when working with strong acids, it is advisable to always carry neutralizers with you: weak alkaline solutions, (baking soda), etc. It is worth remembering that when opening a container with a concentrated acid HCl vapors are formed, which adversely affect the eyes and respiratory system. Therefore, in chemical experiments, it would be best to use a respirator and goggles.
Getting hydrochloric acid
Hydrogen chloride gas is dissolved in water. Hydrogen chloride itself is obtained as follows: hydrogen is burned in chlorine, thereby obtaining a synthetic acid. Or, hydrochloric acid can be obtained using side gases, which are obtained in a number of chemical experiments, for example, when chlorinated hydrocarbons are chlorinated. The acid obtained in this way is called abgasic.
Apply hydrochloric acid in medicine, industry, and also for chemical reactions.
Colorless acid with a pungent odor of hydrogen chloride reacts well with metals. The redox reaction occurs. The reducing agents in the reaction process are metal atoms, and the oxidizing agents are hydrogen cations.
Mainly chemical reactions with metals are accompanied by the release of hydrogen. The intensity of the interaction depends on the activity of the metal, for example, the alkali metal lithium reacts violently, whereas the reaction with aluminum is weak due to the strong oxide film of this element.
Hydrochloric acid and zinc:
2HCl + Zn = ZnCl₂ + H₂
Hydrochloric acid and iron:
2HCl + Fe = FeCl₂ + H₂
Hydrochloric acid and magnesium:
2HCl + Mg = MgCl₂ + H₂
Magnesium chloride, used to clean the roads from ice
With metal oxides, acid forms salt and water:
CuO + 2HCl = CuCl₂ + H₂O
Reaction of hydrochloric acid and calcium carbonate
For the experiment will need:
test tube;
chemical pipette;
solid calcium carbonate (marble);
hydrochloric acid;
gloves;
respirator.
Attention! Do not try this experience yourself!
Conduct the experiment in a well-ventilated area, use caution when working with hydrochloric acid.
Add a few pieces of marble to the vessel and pipette some hydrochloric acid. As a result, there will be an instant reaction with the formation of bubbles - carbon dioxide is released. This is an exchange reaction, the products of which are: a weak and unstable compound, carbonic acid, which decomposes into carbon dioxide and water. The equation of the reaction of dissolution of calcium carbonate in hydrochloric acid:
CaCO₃ + 2HCl (dil.) → CaCl₂ + CO₂ + H₂O
- characteristic of magnesium element: electronic structure, possible oxidation states, basic compounds: oxide, hydroxide, salts. What is carbonization and what is its role in construction.
MgCO 3 = MgO + CO 2
Application.
In industry it is used for the production of refractories, cements, and the purification of petroleum products, as a filler in the production of rubber. Ultra-light magnesium oxide is used as a very fine abrasive for cleaning surfaces, in particular, in the electronics industry.
In medicine, it is used in case of increased acidity of the gastric juice, since it is caused by excessive content of hydrochloric acid. Burnt magnesia is also taken when acid is accidentally released into the stomach.
In the food industry it is registered as a food additive E530.
It is an absolute reflector - a substance with a reflection coefficient equal to one in a wide spectral band. Can be used as an available white standard.
Magnesium hydroxide - The main metal hydroxide is magnesium. Weak insoluble base.
Under standard conditions, magnesium hydroxide is a colorless hexagonal lattice. At temperatures above 350 ° C decomposes into magnesium oxide and water. Absorbs carbon dioxide and water from the air to form the main magnesium carbonate. Magnesium hydroxide is practically insoluble in water, but soluble in ammonium salts. It is a weak base. It occurs in nature in the form of the mineral brucite.
Receipt.
Interaction of soluble magnesium salts with alkalis:
In general:
Mg 2+ + 2OH - = Mg (OH) 2 ¯
Examples:
MgCl 2 + 2NaOH = Mg (OH) 2 ¯ + 2NaCl
Mg (NO 3) 2 + 2KOH = Mg (OH) 2 ¯ + 2KNO 3
The interaction of the solution of magnesium chloride with burnt dolomite:
MgCl 2 + CaO × MgO + 2H 2 O = 2 Mg (OH) 2 ¯ + CaCl 2
Interaction of metallic magnesium with water vapor:
Mg + 2H 2 O = Mg (OH) 2 ¯ + H 2 -
Chemical properties.
Like all weak bases, magnesium hydroxide is thermally unstable. Decomposes when heated to 350 ° C:
Interacts with acids to form salt and water (neutralization reaction):
Mg (OH) 2 + 2HCl = MgCl 2 + 2H 2 O
Mg (OH) 2 + H 2 SO 4 = MgSO 4 + 2H 2 O
Interaction with acidic oxides to form salt and water:
Mg (OH) 2 + SO 3 = MgSO 4 + H 2 O
Interaction with hot concentrated solutions of alkalis with the formation of hydroxymagnesates:
Mg (OH) 2 + 2NaOH = Na 2
Mg (OH) 2 + Sr (OH) 2 = Sr
Application.
Magnesium hydroxide is used to bind sulfur dioxide, as a flocculant for wastewater treatment, as a flame retardant in thermoplastic polymers (polyolefins, PVC), as an additive in detergents, to produce magnesium oxide, sugar refining, as a component of toothpastes.
In medicine, it is used as a medicine to neutralize the acid in the stomach, as well as a very strong laxative.
In the European Union, magnesium hydroxide is registered as a food additive E528.
Magnesium salts.
Most magnesium salts are highly soluble in water. Ion Mg 2+ gives the solutions a bitter taste. Magnesium halides, with the exception of MgF2, are highly hygroscopic - they bleed in air.
Magnesium chloride MgCl 2 (magnesium chloride) anhydrous melts at 718 °. In the presence of traces of water it “smokes” in the air - it decomposes into HCl and MgO. Colorless crystalline hydrates with 1, 2, 4, 6, 8 and 12 water molecules are released from the aqueous solution. In the temperature range from –3.4 to 116.7 °, MgCl 2 × 6H 2 0 crystalline hydrate is stable, which occurs naturally as bischofite mineral, and in large quantities is obtained by evaporation of sea brines. Magnesium chloride forms double salts, of which the mineral carnallite KCl × MgCl 2 × 6H 2 O — the source of magnesium and potassium chloride — is extremely important.
Application.
1. Magnesium chloride is used mainly in the production of metallic magnesium, MgCl 2 × 6H 2 0 is used to obtain magnesia cements.
2. Used for processing ice and snow cover as an additive. As a result of the reaction with snow, it causes melting. It has a 3rd hazard class (moderately hazardous substances) and aggressive corrosive properties.
Magnesium bicarbonate - acidic salt of magnesium and carbonic acid with the formula Mg (HCO 3) 2, exists only in aqueous solutions.
Receipt.
Transmission of carbon dioxide through a suspension of magnesium carbonate:
MgCO 3 + CO 2 + H 2 O = Mg (HCO 3) 2
Physical properties.
Magnesium bicarbonate exists only in aqueous solutions.
The presence of magnesium bicarbonate in water causes its temporary rigidity.
Chemical properties.
When concentrating the solution, magnesium bicarbonate decomposes:
Mg (HCO 3) 2 = MgCO 3 + CO 2 - + H 2 O
Magnesium Hydrophosphate (disubstituted magnesium phosphate) - an acidic salt of magnesium and phosphoric acid with the formula MgHPO 4, slightly soluble in water, forms crystalline hydrates.
Receipt.
The effect of orthophosphoric acid on magnesium oxide or magnesium carbonate:
MgO + H 3 PO 4 = MgHPO 4 + H 2 O
MgCO 3 + H 3 PO 4 = MgHPO 4 + CO 2 - + H 2 O
The action of disubstituted sodium orthophosphate on magnesium chloride:
MgCl 2 + 2Na 2 HPO 4 = MgHPO 4 + 2NaCl
The decomposition of dihydrogen phosphate magnesium:
Mg (H 2 PO 4) 2 = MgHPO 4 + H 3 PO 4
Physical properties.
Magnesium hydrogen phosphate forms white crystals, which are crystalline hydrates: at temperatures up to 225 ° C, MgHPO4 monohydrate is formed. H 2 O, density of 2.32 g / cm³, at the temperature of 36 ° С, MgHPO4 trihydrate is formed. 3H 2 O, density 2.10 g / cm³, with room temperature MgHPO4 heptahydrate is formed. 7H 2 O.
Chemical properties.
When heated goes into pyrophosphate:
Application.
Used in food supplement E343.
Magnesium dihydrogen phosphate - acidic salt of the metal of magnesium and orthophosphoric acid with the formula Mg (H 2 PO 4) 2, colorless hygroscopic crystals, soluble in water, forms crystalline hydrates.
Receipt.
Dissolution of hydroxide or magnesium oxide in orthophosphoric acid:
Physical properties.
Magnesium dihydrogen phosphate forms colorless crystals.
Formed crystalline hydrate composition of Mg (H 2 PO 4) 2. nH 2 O, where n = 2, 4, 6.
Magnesium carbide - binary inorganic compound of magnesium and carbon with the formula MgС 2. Also known magnesium carbide with the formula Mg 2 C.
Receipt.
Sintering magnesium fluoride and calcium carbide:
Flowing acetylene over magnesium powder:
By restoring pentane with magnesium powder at 650 ° C, more complex carbide Mg 2 C 3 can be obtained.
Chemical properties.
When heated decomposes with the formation of intermediate carbide Mg2C3:
Interacts with water:
Magnesium carbonate, magnesium carbonate, MgCO 3 - magnesium salt of carbonic acid.
Properties
White crystals, density 3,037 g / cm ³. At 500 ° C it is noticeable, and at 650 ° C it is completely decomposed into MgO and CO2. The solubility of magnesium carbonate in water is insignificant (22 mg / l at 25 ° C) and decreases with increasing temperature. When CO 2 is saturated with an aqueous suspension of MgCO 3, the latter is dissolved due to the formation of Mg (HCO 3) 2 bicarbonate. From aqueous solutions in the absence of an excess of CO 2, basic magnesium carbonates are emitted. With carbonates of a number of metals, magnesium carbonate forms double salts, which include the natural mineral dolomite MgCO 3 · CaCO 3.
Prevalence in nature.
Magnesium carbonate is widely distributed in nature in the form of the mineral magnesite.
Application.
The basic magnesium carbonate 3MgCO 3 · Mg (OH) 2 · 3H 2 O (the so-called white magnesia) is used as a filler in rubber compounds for the manufacture of thermal insulation materials.
Magnesium carbonate is necessary in the production of glass, cement, bricks.
Magnesium nitrate Mg (NO 3) 2 - colorless hygroscopic crystals with a cubic lattice; melting point 426 ° C (with decomposition). Solubility in water (g per 100 g): 73.3 (20 ° C), 81.2 (40 ° C), 91.9 (60 ° C). Also soluble in ethanol, methanol, liquid NH3. Depending on the concentration, nona-, hexa- and dihydrates crystallize from aqueous solutions.
Component of complex fertilizers, since Magnesium is part of chlorophyll, which is necessary for photosynthesis, increases the activity of many enzymes and acts as a phosphorus transporter. High solubility and low electrical conductivity make the product extremely suitable for foliar feeding and fertigation, especially when using irrigation waters with a high salt concentration. Fertilizer is used for root and foliar nutrition of vegetables, berries, fruit crops, grapes; oxidizer in pyrotechnic compositions.
Carbonization- saturation of any solution with carbon dioxide. Used in construction.
Mineral carbonation - silicic acid in silicates is replaced by carbonic acid to form carbonates. Of carbonates, the rock-forming mineral in sedimentary rocks is calcite (lime spar) CaCO3 and is more common. Magnesite - MgCO3 and dolomite - CaMg (CO3) 2 are less common. AT clean water, not containing carbonic acid, calcite is dissolved in a small amount (0.03 g per liter of water); magnesite is practically insoluble. If water contains carbon dioxide, calcite dissolves easily with the formation of acidic calcium carbonate, soluble in water - Ca (HCO3) 2.
Carbonization is a change that occurs in concrete on Portland cement when exposed to C0 2 air. Calcium hydroxide Ca (OH) 2 in the presence of moisture is particularly affected. Calcium hydroxide is converted to calcium carbonate when it absorbs carbon dioxide. Calcium carbonate is poorly soluble in water and, as a result, tends to hermetically close the pores on the surface of the concrete (meaning dense, waterproof concrete).
Typically, the pH of the pore water in concrete ranges from 10.5 to 11.5. If due to carbonization it decreases to 9 and below, then corrosion of the reinforcement is possible. Therefore, the thickness of the carbonized layer is an important factor in protecting the reinforcement: the deeper the carbonization, the greater the danger of corrosion of the steel. The depth of carbonation can be determined by treating concrete with phenolphthalein. The presence of alkaline properties under the action of phenolphthalein is indicated by the appearance of a pink color, while the carbonated concrete retains its original color.
High-quality dense concrete undergoes carbonization very slowly. It is unlikely that carbonization will be observed at a depth of more than 5-10 mm even after operation for 50 years. On the other hand, the carbonization depth of low-strength permeable concrete can reach 25 mm in less than 10 years. Experience shows that low-quality concrete products are particularly susceptible to carbonization.
- characteristic of calcium element: electronic structure, possible oxidation states, main compounds: oxide, hydroxide, salts.
Calcium - an element of the main subgroup of the second group, the fourth period of the periodic table of chemical elements DI Mendeleev, with atomic number 20. It is denoted by the symbol Ca (lat. Calcium). Electronic structure 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 = [18 Ar] 4s 2, oxidation state +2, 0. Refers to alkaline earth metals.
Simple substance calcium is a soft, chemically active alkaline earth metal of silver-white color. Industrial production: electrolysis of molten calcium chloride.
Calcium Oxide CaO - basic oxide, quicklime. White, hygroscopic. Refractory, thermally unstable, volatile during ignition. Vigorously reacts with water (with a high exo-effect), forms a strongly alkaline solution, the process is called lime slaking. Reacts with acids, metal oxides, non-metals. It is used to synthesize other calcium compounds, a component of binding materials in construction.
Production in industry - limestone firing (900 - 1200 o C)
Calcium hydroxide Ca (OH) 2 - hydrated lime, basic hydroxide. Decomposed with moderate heating. White, hygroscopic. Absorbs moisture and carbon dioxide from the air. Slightly soluble in the cold. water, even less - in boiling water. A clear solution (lime water) quickly becomes cloudy due to precipitation of hydroxide (the suspension is called milk of lime). Qualitative reaction is the transmission of carbon dioxide through lime water with the appearance of CaCO3 sediment and its transition into solution. Reacts with acids and acid oxides, enters into ion exchange reactions.
It is used in construction for the preparation of lime mortar (sand + slaked lime + water), which serve as a bonding material for stone and brickwork, finishing (plastering) walls and other construction purposes. The solidification of such solutions is due to the absorption of CO2 from the air.
Ca (OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O
Ca (OH) 2 + H 2 SO 4 → CaSO 4 + 2H 2 O,
Reacts with salts if a precipitate forms:
Ca (OH) 2 + Na 2 SO 3 → CaSO 3 ↓ + 2NaOH
Calcium salts.
Calcium sulfate (CaSO 4) - inorganic compound, calcium salt of sulfuric acid.
Is found in nature as a CaSO 4 dihydrate? 2H 2 O (gypsum, selenite) and in the anhydrous state - anhydrite.
Calcium chloride, CaCl2 - calcium salt of hydrochloric acid.
Possesses high hygroscopic properties. Solubility (g per 100 g H2O): 74 (20 ° C) and 159 (100 ° C). Calcium chloride aqueous solutions freeze at low temperatures (20% at –18.57 ° C, 30% at –48 ° C).
Forms a hydrate of CaCl2 · 6H2O, stable up to 29.8 ° C; at higher temperatures, crystalline hydrates with 4, 2, and 1 H2O molecules fall out of the saturated solution. When CaCl2 * 6H2O (58.8%) is mixed with snow or ice (41.2%), the temperature drops to -55 ° C (cryohydrate point).
Calcium chloride is obtained as a by-product in the production of soda.
In the chemical laboratory, calcium chloride is used as a filler for drying tubes, also called calcium chloride, intended to isolate substances in the vessel from atmospheric water vapor and for drying gases.
Calcium chloride is also used as an accelerator for setting cement;
Calcium carbonate (calcium carbonate) - inorganic chemical compound, salt of carbonic acid and calcium. Chemical formula —CaCO 3. In nature, it is found in the form of minerals - calcite, aragonite and vaterite, is the main component of limestone, marble, chalk, is part of the shell of eggs. Insoluble in water and ethanol.
Putty, various sealants - all of them contain calcium carbonate in significant quantities. Also, calcium carbonate is an essential component in the production of household chemicals.
Calcium carbonate is also widely used in cleaning systems, as a means of combating environmental pollution, and with the help of calcium carbonate, the acid-base balance of the soil is restored.
- Examples illustrating the use of oxides and hydroxides of calcium and magnesium in construction.
Calcium oxide and hydroxide:
When whitewashing rooms.
When whitewashing wooden fences and smearing rafters - to protect against rotting and fire.
For the preparation of lime mortar. Lime has been used for building masonry since ancient times. The mixture is usually prepared in this proportion: three or four parts of sand (by weight) are added to one part of a mixture of calcium hydroxide (hydrated lime) and water. When this happens, the mixture hardens by the reaction: Ca (OH) 2 + CO2 → CaCO3 ↓ + H2O. This is an exothermic reaction, the energy release is 27 kcal (113 kJ).
As can be seen from the reaction, water is released during it. This is a negative factor, since in rooms built with lime mortar, high humidity persists for a long time. In this regard, as well as due to a number of other advantages over calcium hydroxide, cement has practically superseded it as a binder for building solutions. Moreover, it is also unacceptable for use when laying stoves, because under the influence of high temperatures, suffocating carbon dioxide is released.
For the preparation of silicate concrete. The composition of silicate concrete is identical with the composition of lime mortar; however, it is prepared by another method - a mixture of calcium oxide and quartz sand is not treated with water, but with superheated (174.5-197.4 ° C) water vapor in an autoclave at a pressure of 9-15 atmospheres.
In the manufacture of silicate bricks.
Oxide and magnesium hydroxide:
for the production of combined systems of refractory materials (magnesite building boards), for the production of cements. Magnesium oxide (caustic magnesite) is used as a binder, which, when mixed with MgCl2 solution, is able to quickly harden and gain strength in air.
- hardness of natural waters: definition, types of hardness, methods for removing hardness of water: physical, chemical (reaction equations), physico-chemical.
Natural water containing a large amount of calcium or magnesium salts in a solution is called hard water as opposed to soft water containing little or no calcium and magnesium salts.
The first of these is due to the presence of calcium and magnesium bicarbonates, the second to the presence of salts of strong acids, sulphates or chlorides of calcium and magnesium. With prolonged boiling of water with carbonate hardness, a precipitate appears in it, consisting mainly of CaCO3, and at the same time CO2 is released.
Both of these substances appear as a result of the decomposition of calcium carbonate:
Therefore, carbonate stiffness is also called temporary stiffness. Quantitatively, the temporary rigidity is characterized by the content of bicarbonates removed from the water when it is boiled for an hour. The stiffness remaining after such boiling is called constant stiffness.
Water hardness is expressed by the sum of milliequivalents of calcium and magnesium ions contained in water. One milliequivalent of stiffness corresponds to a content of 20.04 mg / l or 12.16 mg / l.
The hardness of natural waters varies widely. It is different in different reservoirs, and in the same river varies throughout the year (minimal during the flood). The hardness of the waters of the seas is much higher than rivers and lakes. Thus, the Black Sea water has a total hardness of 65.5 meq / l. The average value of the hardness of the water of the world ocean is 130.5 meq / l (including 22.5 meq / l per meq / l).
The presence in water of a significant amount of calcium or magnesium salts makes water unsuitable for many technical purposes. Thus, with prolonged feeding of steam boilers with hard water, their walls gradually become covered with a dense crust of nakiii. Such a crust already at a layer thickness in greatly reduces the transfer of heat by the walls of the boiler and, consequently, leads to an increase in fuel consumption. In addition, it can cause blistering and cracking both in the heating pipes and on the walls of the boiler itself.
Hard water does not give foam with soap, as the soluble sodium salts of fatty acids — palmitic and stearic — contained in soap are transformed into insoluble calcium salts of the same acids:
Hard water can not be used when carrying out some technological processes, for example, when dyeing.
The constant hardness of water is due to the presence in it mainly of sulphates and chlorides of calcium and magnesium and is not eliminated by boiling. The sum of the temporary (removable) and constant hardness is the total hardness of the water.
There are various ways to determine stiffness.
Consider two of them:
1) determination of temporal rigidity using a titrated solution of hydrochloric acid
2) complexometric method for determining the total stiffness.
During the titration of a sample of water with hydrochloric acid in the presence of methyl orange, the decomposition of bicarbonates occurs, causing temporary rigidity:
Method of determination. 100 ml of the test water are taken in a conical flask with a pipette or a measuring cylinder, 2-3 drops of methyl orange are added and titrated with 0.1 and. HCl solution until orange color appears.
Calculation result analysis. 1 ml 0.1 n. HCl solution corresponds to 0.1 / 1000 g-eq or 0.1 mg-eq Ca 2+. V (HCl) corresponds to 0.1 V (HCl) / 1000 g-eq or 0.1 V (HCl) mg-eq Ca 2+. 0.1 V (HCl) mEq is in the volume of V A. To express the rigidity in milligram-equivalents per 1 l of water, you need to divide the value found by V A and multiply it by 1000, i.e. the hardness of the water under study is equal to:
Methods of elimination.
Thermal softening. Based on water boiling, as a result of thermally unstable calcium and magnesium bicarbonates decompose with the formation of scale:
Ca (HCO3) 2 → CaCO3 ↓ + CO2 + H2O.
Boiling removes only temporary (carbonate) hardness. Finds application in life.
Reagent softening. The method is based on the addition of soda ash Na2CO3 or hydrated lime Ca (OH) 2 to the water. At the same time, calcium and magnesium salts pass into insoluble compounds and, as a result, precipitate.
For example, the addition of hydrated lime leads to the conversion of calcium salts to insoluble carbonate:
Ca (HCO3) 2 + Ca (OH) 2 → 2CaCO3 ↓ + 2H2O
The best reagent for eliminating the overall hardness of water is sodium orthophosphate Na3PO4, which is part of most household and industrial products:
3Ca (HCO3) 2 + 2Na3PO4 → Ca3 (PO4) 2 ↓ + 6NaHCO3
3MgSO4 + 2Na3PO4 → Mg3 (PO4) 2 ↓ + 3Na2SO4
Calcium and magnesium orthophosphates are very poorly soluble in water, and therefore easily separated by mechanical filtration. This method is justified at relatively high water consumption, since it involves solving a number of specific problems: sediment filtration, accurate reagent dosage.
Cationization. The method is based on the use of ion-exchange granular loading (most often ion-exchange resins). Such a load on contact with water absorbs cations of hardness salts (calcium and magnesium, iron and manganese). Instead, depending on the ionic form, it gives away ions of sodium or hydrogen. These methods are respectively called Na-cationization and H-cationization. With properly selected ion-exchange loading, the water hardness decreases with single-stage sodium cationization to 0.05-0.1 ° W, with two-stage loading - to 0.01 ° W. In industry, ion-exchange filters replace calcium and magnesium ions with sodium and potassium ions, producing soft water.
Reverse osmosis . The method is based on the passage of water through a semipermeable membrane (usually polyamide). Together with the salts of hardness, most of the other salts are removed. The cleaning efficiency can reach 99.9%.
There are nanofiltration (the nominal diameter of the holes of the membrane is equal to the units of nanometers) and picofiltration (the nominal diameter of the holes of the membrane is equal to the units of picometers).
As disadvantages of this method should be noted:
The need for pre-treatment of water supplied to the reverse osmosis membrane;
The relatively high cost of 1 liter of water produced (expensive equipment, expensive membranes);
Low mineralization of the produced water (especially when picofiltration). Water becomes almost distilled.
Electrodialysis It is based on the removal of salts from water under the action of an electric field. Removal of ions of dissolved substances occurs due to special membranes. Just as with the use of reverse osmosis technology, the removal of other salts, in addition to the hardness ions, occurs.
Completely clean water from hardness salts can be distilled.