Receipt
- Interaction of selenium(VI) oxide with water:
texvc not found; See math/README for setup help.): \mathsf(SeO_3 + H_2O \longrightarrow H_2SeO_4)
- Interaction of selenium with chlorine or bromine water:
Unable to parse expression (executable file texvc not found; See math/README for setup help.): \mathsf(Se + 3 Cl_2 + 4 H_2O \longrightarrow H_2SeO_4 + 6 HCl)
Unable to parse expression (executable file texvc not found; See math/README for setup help.): \mathsf(Se + 3 Br_2 + 4 H_2O \longrightarrow H_2SeO_4 + 6 HBr)
- Interaction of selenous acid or selenium (IV) oxide with hydrogen peroxide:
Unable to parse expression (executable file texvc not found; See math/README for setup help.): \mathsf(SeO_2 + H_2O_2 \longrightarrow H_2SeO_4 )
Unable to parse expression (executable file texvc not found; See math/README for setup help.): \mathsf(H_2SeO_3 + H_2O_2 \longrightarrow H_2SeO_4 + H_2O )
Chemical properties
- Color change of acid-base indicators
- Hot, concentrated selenic acid is able to dissolve gold, forming a red-yellow solution of gold(III) selenate:
Unable to parse expression (executable file texvc not found; See math/README for setup help.): \mathsf(2Au + 6 H_2SeO_4 \longrightarrow Au_2(SeO_4)_3 + 3 H_2SeO_3 + 3 H_2O)
To obtain an anhydrous acid in a solid crystalline state, the resulting solution is evaporated at a temperature below 140 ° C (413 K, 284 ° F) in vacuum.
Concentrated solutions of this acid are viscous. Crystalline mono- and dihydrates are known. The monohydrate melts at 26°C, the dihydrate at -51.7°C.
selenates
Salts of selenic acid are called selenates:
- Ammonium selenate - (NH 4) 2 SeO 4
- Gold (III) selenate - Au 2 (SeO 4) 3
- Sodium selenate - Na 2 SeO 4
Application
Selenic acid is mainly used for the preparation of selenates.
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Notes
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An excerpt characterizing Selenic acid
Apparently Christina had similar thoughts, because she suddenly asked me for the first time:– Please do something!
I immediately answered her: “Of course!” And I thought to myself: “If I only knew - what !!!” ... But I had to act, and I decided that I would try until I achieved something - or he would finally hear me, or (in the worst case) again put out the door.
So are you going to talk or not? I asked deliberately. “I don’t have time for you, and I’m only here because I have this wonderful little man with me - your daughter!”
The man suddenly flopped down in a nearby chair and, clasping his head in his hands, sobbed ... This went on for quite a long time, and it was clear that he, like most men, did not know how to cry at all. His tears were mean and heavy, and they were given to him, apparently, very, very hard. It was only here that I really understood for the first time what the expression “male tears” means ...
I sat down on the edge of some bedside table and bewilderedly watched this stream of other people's tears, having absolutely no idea what to do next? ..
- Mom, mommy, why are such monsters walking around here? a frightened voice asked softly.
And only then I noticed very strange creatures that literally “heaps” curled around the drunken Arthur ...
My hair began to stir - these were the real "monsters" from children's fairy tales, only here for some reason they even seemed very, very real ... They looked like evil spirits released from a jar that somehow managed to "attach" directly to the poor man’s breasts, and, hanging on him in clusters, with great pleasure “devoured” his almost exhausted life force ...
I felt that Vesta was scared to the point of a puppy squeal, but she was trying her best not to show it. The poor thing watched in horror as these terrible "monsters" with pleasure and ruthlessly "ate" her beloved dad right in front of her eyes ... I just could not figure out what to do, but I knew that I had to act quickly. After a quick look around and not finding anything better, I grabbed a pile of dirty plates and threw them on the floor with all my might ... Arthur jumped up in his chair in surprise and stared at me with crazy eyes.
- There is nothing to sag! I shouted, “Look what “friends” you have brought to your house!
I was not sure if he would see the same thing that we saw, but it was my only hope to somehow "wake him up" and thus make him at least a little sober.
By the way his eyes suddenly popped onto his forehead, it turned out that he saw ... In horror, he shied away into a corner, he could not take his eyes off his "cute" guests and, unable to utter a word, only pointed at them with a trembling hand. He was shaking slightly, and I realized that if nothing was done, the poor man would have a real nervous attack.
I tried to mentally refer to these strange monstrous creatures, but nothing good came of it; they just “growled” ominously, waving me off with their clawed paws, and without turning around, sent a very painful energy blow right into my chest. And right there, one of them “unstuck” from Arthur and, having looked, as he thought, the easiest prey, jumped right on Vesta ... The girl screamed wildly in surprise, but - we must pay tribute to her courage - she immediately began to fight back, which was forces. Both of them, he and she, were the same incorporeal beings, so they “understood” each other perfectly and could freely inflict energy blows on each other. And one should have seen with what excitement this fearless little girl rushed into battle! .. From the poor cowering "monster" only sparks fell from her violent blows, and we, the three watching, were so dumbfounded to our shame that we did not immediately react to at least to help her somehow. And just at the same moment, Vesta became like a completely squeezed out golden lump and, becoming completely transparent, disappeared somewhere. I realized that she had given up all her childish strengths, trying to defend herself, and now she didn’t have enough of them to simply maintain contact with us ... Christina looked around in confusion - apparently her daughter didn’t have the habit of disappearing so easily, leaving her alone. I also looked around and then ... I saw the most shocked face that I had ever seen in my life both then and for all subsequent long years ... Arthur stood in real shock and looked directly at his wife! .. Apparently too much alcohol , huge stress, and all subsequent emotions, for a moment opened the “door” between our different worlds and he saw his deceased Christina, as beautiful and as “real” as he always knew her ... No words would be possible describe the expressions in their eyes! .. They did not speak, although, as I understood, Arthur most likely could hear her. I think that at that moment he simply could not speak, but everything was in his eyes - and the wild pain that had choked him for so long; and deafening him with its unexpectedness, boundless happiness; and prayer, and so much more that there would be no words to try to tell it all! ..
Selenium was discovered in 1817 by Jens Jakob Berzelius. The story of Berzelius himself about how this discovery came about has been preserved: “I investigated, in collaboration with Gottlieb Hahn, the method that is used to produce sulfuric acid in Gripsholm. We found a precipitate in sulfuric acid, partly red, partly light brown. ... Curiosity , inspired by the hope of discovering a new rare metal in this brown precipitate, led me to investigate the precipitate... I found that the mass (i.e., the precipitate) contains a hitherto unknown metal, very similar in its properties to tellurium. According to this analogy I called the new body selenium (Selenium) from the Greek selhnh(moon), since tellurium is named after Tellus - our planet ".
Being in nature, getting:
The content of selenium in the earth's crust is about 500 mg/t. Selenium forms 37 minerals, among which ashavalite FeSe, claustalite PbSe, timannite HgSe, guanahuatite Bi 2 (Se,S) 3 , hastite CoSe 2 , platinum PbBi 2 (S, Se) 3 should be noted first of all. Occasionally, native selenium is found. Sulfide deposits have the main industrial value for selenium. The content of selenium in sulfides ranges from 7 to 110 g/t. The concentration of selenium in sea water is 4*10 -4 mg/l.
Selenium is obtained from waste products of sulfuric acid, pulp and paper production, and also significant amounts are obtained from the sludge of copper-electrolyte production, in which selenium is present in the form of silver selenide. Several methods are used to obtain selenium from sludge: oxidative roasting with sublimation of SeO 2 ; oxidative sintering with soda, conversion of the resulting mixture of selenium compounds to Se(IV) compounds and their reduction to elemental selenium by the action of SO 2 .
Physical properties:
The diversity of the molecular structure determines the existence of selenium in various allotropic modifications: amorphous (powdered, colloidal, vitreous) and crystalline (monoclinic, a- And b-shape and hexagonal g-form). Amorphous (red) powdered and colloidal selenium is obtained by reduction from a solution of selenous acid by rapid cooling of selenium vapor. Vitreous (black) selenium is obtained by heating any modification of selenium above 220°C, followed by rapid cooling. It has a vitreous luster and is fragile. Thermodynamically the most stable is hexagonal (gray) selenium. It is obtained from other forms of selenium by heating to melting with slow cooling to 180-210°C and holding at this temperature. Its lattice is built from parallel helical chains of atoms.
Chemical properties:
At ordinary temperatures, selenium is resistant to oxygen, water and dilute acids. When heated, selenium interacts with all metals, forming selenides. In oxygen, with additional heating, it slowly burns with a blue flame, turning into SeO 2 dioxide.
With halogens, with the exception of iodine, it reacts at room temperature to form compounds SeF 6 , SeF 4 , SeCl 4 , Se 2 Cl 2 , SeBr 4 , etc. Selenium reacts with chlorine or bromine water according to the equation:
Se + 3Br 2 + 4H 2 O \u003d H 2 SeO 4 + 6 HBr
Hydrogen interacts with selenium at t>200°C, giving H 2 Se.
In conc. H 2 SO 4 in the cold, selenium dissolves, giving a green solution containing polymer cations Se 8 2+.
With water when heated and in conc. solutions of alkalis, selenium disproportionates:
3Se + 3H 2 O = 2H 2 Se + H 2 SeO 3 and 3Se + 6KOH = K 2 SeO 3 + 2K 2 Se + 3H 2 O
forming compounds of selenium (-2) and selenium (+4).
Similarly, selenium sulfur dissolves when heated in solutions of Na 2 SO 3 or KCN, forming, respectively, Na 2 SSeO 3 (analogue of thiosulfate) or KCNSe (analogue of thiocyanate).
The most important connections:
For selenium, the most characteristic oxidation states are -2, +4, +6.
Selenium(IV) oxide SeO 2- white shiny crystals with a polymer molecule (SeOsub> 2) sub> n, tpl. 350°C. The vapors are yellowish-green in color and smell like rotten radish. Easily soluble in water to form H 2 SeO 3 .
Selenic acid, H 2 SeO 3- white rhombic crystals. Possesses high hygroscopicity. Well soluble in water. Unstable, when heated above 70°C, it decomposes into water and selenium(IV) oxide. Salts are selenites.
Sodium selenite, Na 2 SeO 3 are colorless crystals, mp. 711°C. Hygroscopic, soluble in water. When heated in an inert atmosphere, it decomposes into oxides. When heated in air, it oxidizes to selenate: 2Na 2 SeO 3 + O 2 = 2Na 2 SeO 4
Selenium(VI) oxide SeO 3- - colorless crystals, mp. 121°C. It is hygroscopic, reacts with water with high heat release and formation of H 2 SeO 4 . Strong oxidizing agent, reacts violently with organic substances
Selenic acid, H 2 SeO 4- a colorless crystalline substance, highly soluble in water. Poisonous, hygroscopic, is a strong oxidizing agent. Selenic acid is one of the few compounds that, when heated, dissolve gold, forming a red-yellow solution of gold(III) selenate.
2Au + 6H 2 SeO 4 = Au 2 (SeO 4) 3 + 3H 2 SeO 3 + 3H 2 O
selenates- salts of selenic acid. Sodium selenate Na 2 SeO 4 - rhombic crystals; tpl. 730 °C. Prepared by neutralization of an acid with sodium oxide, hydroxide or carbonate or by oxidation of sodium selenite. Slightly soluble in water, below 32 ° C crystallizes from aqueous solutions in the form of decahydrate Na 2 SeO 4 10H 2 O
Hydrogen selenide, H 2 Se It is a colorless flammable gas with an unpleasant odour. The most toxic compound of selenium. In air, it is easily oxidized at ordinary temperature to free selenium. It is also oxidized to free selenium by chlorine, bromine and iodine. When burned in air or oxygen, selenium(IV) oxide and water are formed. Stronger acid than H 2 S.
selenides- compounds of selenium with metals. Crystalline substances, often with a metallic sheen. There are monoselenides of the composition M 2 Se, MSe; polyselenides M 2 Se n (except Li), where n = 2-6; hydroselenides MHSe. Air oxygen is oxidized to selenium: 2Na 2 Se n + O 2 + 2H 2 O \u003d 2n Se + 4NaOH
Application:
Selenium is used in rectifier semiconductor diodes, as well as for photoelectric devices, electrophotographic copiers, as phosphors in television, optical and signal devices, thermistors, etc. Selenium is widely used to decolorize green glass and obtain ruby glasses; in metallurgy - to give steel a fine-grained structure, improve their mechanical properties; in the chemical industry - as a catalyst.
The stable selenium-74 isotope made it possible, on its basis, to create a plasma laser with colossal amplification in the ultraviolet region (about a billion times).
The radioactive isotope selenium-75 is used as a powerful source of gamma radiation for flaw detection.
Biological role and toxicity:
Selenium enters the active sites of some proteins in the form of the amino acid selenocysteine. It has antioxidant properties, increases the perception of light by the retina, affects many enzymatic reactions. The requirement of man and animals for selenium does not exceed 50-100 mcg/kg of diet.
Polkovnikov A.A.
KhF Tyumen State University, 581 groups. 2011
Website "Handbook of a chemist":
§ 12. Oxoacids of chalcogens E(VI): preparation, structure, properties.
Oxoacids of chalcogens(VI) H 2 SO 4 , H 2 SeO 4 and H 6 TeO 6 are synthesized by the oxidation of their dioxides (or their corresponding acids):
H 2 SeO 3 + H 2 O 2 H 2 SeO 4 + H 2 O
5TeO 2 + 2KMnO 4 + 6HNO 3 + 12 H 2 O 5H 6 TeO 6 + 2KNO 3 + 2Mn(NO 3) 2,
as well as the oxidation of simple substances with strong oxidizing agents:
5Te + 6HClO 3 + 12H 2 O 5H 6 TeO 6 + 3Cl 2,
or exchange reactions:
BaTeO 4 + H 2 SO 4 + 2H 2 O H 6 TeO 6 + BaSO 4 .
In the H 2 SO 4 molecule, sulfur is tetrahedrally surrounded by two hydroxyl (OH) groups and two oxygen atoms. The bond lengths (the S-OH distance is 1.54 and the S-O distance is 1.43) in the H 2 SO 4 molecule are such that the S-O bonds can be considered double, and the S-OH bonds single. Colorless, ice-like H 2 SO 4 crystals have a layered structure, in which each H 2 SO 4 molecule is connected to four neighboring molecules by strong hydrogen bonds, forming a single spatial frame. At a temperature of 10.48 o C, H 2 SO 4 melts with the formation of a heavy (d = 1.838 g / ml at 15 o C) oily liquid boiling at 280 o C. Liquid H 2 SO 4 has a structure almost the same as that of a solid, only the integrity of the spatial frame is broken, and it can be represented as a set of microcrystals constantly changing their shape. H 2 SO 4 is miscible with water in any ratio, which is accompanied by the formation of H 2 SO 4 hydrates. nH2O (Fig. 8). The heat of hydration is so great that the mixture may even boil.
Fig.8. T-x diagram of the H 2 O-H 2 SO 4 system.
Liquid H 2 SO 4 is surprisingly similar to water with all the structural features and anomalies. Here is the same system of strong hydrogen bonds as in water, almost the same strong spatial frame, the same abnormally high viscosity, surface tension, melting and boiling points. The dielectric constant of H 2 SO 4 is large ( 100). For this reason, the intrinsic dissociation ( autoionization) for sulfuric acid is noticeably higher than for water: 2H 2 SO 4 H 3 SO 4 + + HSO 4-, K = 2.7 . 10 -4 .
Due to the high polarity, the H-O bond is easily broken, and the elimination of a proton requires less energy than water. For this reason, the acidic properties of H 2 SO 4 are pronounced and, when dissolved in anhydrous H 2 SO 4, most of the compounds traditionally considered acids (CH 3 COOH, HNO 3, H 3 PO 4, etc.) behave like bases, entering in the neutralization reaction and increasing the concentration of anions:
H 2 O + H 2 SO 4 H 3 O + +,
base
CH 3 COOH + H 2 SO 4 CH 3 C (OH) 2 + +,
base
HNO 3 + 2 H 2 SO 4 NO 2 + + H 3 O + +2,
base
Only a few compounds (HClO 4, FSO 3 H) when dissolved in H 2 SO 4 behave like weak acids, that is, their proton is split off more easily than that of H 2 SO 4, which leads to an increase in the concentration of the solvated proton, for example,
HSO 3 F + H 2 SO 4 + SO 3 F-.
Some properties of oxoacids of chalcogens (VI) are given in Table 9.
Table 9. Properties of oxoacids of E(VI) chalcogens.
H2TeO4. 2H 2 O=H 6 TeO 6 |
|||
| pK 1: H 2 EO 4 =
H + + NEO 4 - pK2: |
|||
| E o, B; pH = 0: | |||
| E o, B; pH = 14: |
Sulfuric and selenic acids are strong dibasic acids and are similar in structure and properties to each other. Their dissociation constants in aqueous solutions are of the same order (K 2 for and are equal to 1.2.10 -2 and 2.19.10 -2, respectively), selenates are isomorphic with sulfates), forming, for example, alum of the composition MAl (SeO 4) 3 . 12H 2 O, where M - heavy alkali metal .
Structure orthotelluric acid H 6 TeO 6 differs from the structure of sulfuric and selenic acids (compare with the oxygen acids of the halogens HClO 4 , HBrO 4 and H 5 IO 6). The crystal structure of solid H 6 TeO 6 (mp 136 o C) is built from regular octahedral molecules, which retain their shape in solutions. Tellurates are not isomorphic with sulfates and selenates. Orthotelluric acid is titrated with alkali as a monobasic acid with the formation of salts M I TeO (OH) 5, it is weaker than carbonic acid. Complete (Ag 6 TeO 6 , Na 6 TeO 6) and partial (NaH 5 TeO 6 , Na 2 H 4 TeO 6 , Na 4 H 2 TeO 6) products have been obtained. replacement of protons by metal ions.
Selenic acid a stronger oxidizing agent than H 2 SO 4 and H 6 TeO 6 (Table 9). It dissolves Cu and even Au without heating: 2Au + 6H 2 SeO 4 Au 2 (SeO 4) 3 + 3 H 2 SeO 3 + 2H 2 O, oxidizes halide ions, except for fluoride, to free halogens, under its action fiber ignites. Orthotelluric acid is also a stronger oxidizing agent than sulfuric acid. The most frequent reduction product is H 2 SeO 4 and H 6 TeO 6 are simple substances.
Sulfuric acid has strong oxidizing properties only in concentrated form and when heated:
Cu + 2 H 2 SO 4 CuSO 4 + SO 2 + 2H 2 O.
The products of its recovery, depending on the reaction conditions, can be SO 2 (with an excess of H 2 SO 4), H 2 S, S,, polythionates (with a lack of H 2 SO 4).
In the - - H 5 Te series, an anomaly is observed in the sequence of changes in thermodynamic stability and oxidizing ability: selenic acid and its salts are thermodynamically less stable and stronger oxidizing agents than the corresponding acids and salts of S(VI) and Te(VI). Slope of a line connecting volt-equivalent pairs 
, greater than the slope of the corresponding lines for H 6 TeO 6- H 2 TeO 3 and - H 2 SO 3 (Fig. 7). The higher potential of the / pair compared to the H 6 TeO 6 / H 2 TeO 3 and / H 2 SO 3 pairs leads to the fact that H 2 SeO 4, for example, releases chlorine from concentrated HCl: H 2 SeO 4 + 2HCl \u003d \u003d Cl 2 + H 2 SeO 3 + H 2 O. Similar nonmonotonic changes in the properties of elements and their compounds, in particular, oxo acids, are also observed for other elements of the 4th period, for example, 
, and are sometimes called secondary periodicity. It can be assumed that the anomalies under consideration are associated with a decrease in the strength of the Se-O bond compared to the S-O bond. In turn, this is caused by an increase in the size and energies of the 4s and 4p orbitals of the selenium atom compared to the size and energies of the 2s -orbitals of oxygen, and therefore, with a decrease in the interaction (overlap) 4s-,
4p -
orbitals of selenium and 2s, 2p-orbitals of oxygen (the energies of 2s-, 2p-, 3s-, 3p-, 4s- and 4p-atomic orbitals are - 32.4, - 15.9, - 20.7, - 12.0, - 17.6 and - 9.1 eV, respectively). An increase in the stability and a decrease in the oxidizing ability of oxo compounds upon passing from Se(VI) to Te(VI )
due to structural features and an increase in the strength of the Te-O bond in octahedral TeO 6 ions compared to the Se-O bond in tetrahedra. The tellurium atom, compared to the selenium atom, has a larger radius; it is characterized by a coordination number of 6. An increase in the number of coordinated oxygen atoms leads to an increase in the number of electrons in the bonding molecular orbitals and, accordingly, to an increase in the bond strength.
Selenic acid is an inorganic substance consisting of the selenate anion and a hydrogen cation. Its chemical formula is H 2 SeO 4 . Selenic acid, like any other compound, has unique properties due to which it has found wide application in certain areas. And this should be told in more detail.
General characteristics
Selenic acid belongs to the class of strong. Under standard conditions, it appears as colorless crystals, which are highly soluble in water. This substance must be feared, as it is poisonous and hygroscopic (absorbs water vapor from the air). Also, this compound is a powerful oxidizing agent. Other features can be listed as follows:
- The molar mass is 144.97354 g/mol.
- The density is 2.95 g/cm³.
- The melting point reaches 58°C and the boiling point reaches 260°C.
- The dissociation constant index is -3.
- Solubility in water is reached at 30 °C.
Interestingly, selenic acid is one of the few substances that can dissolve gold. This list also includes cyanide, Lugol's solution and aqua regia. But of the acids, it is the only one.
Getting a substance
Most often, selenic acid is synthesized according to the formula SeO 3 + H 2 O → H 2 SeO 4. It displays the interaction of water and selenium oxide. It is an inorganic substance that is easily soluble in acetic anhydride, sulfuric acid, and also in sulfur dioxide. By the way, a selenium compound can decompose into oxide and water under the influence of phosphoric anhydride (P 2 O 5).
In addition, acid is also obtained as a result of reactions when the main substance interacts with chlorine or bromine water. Here are the formulas for selenic acid in these two cases:
- Se + 3Cl 2 + 4H 2 O → H 2 SeO 4 + 6HCl.
- Se + Br 2 + 4H 2 O → H 2 SeO 4 + 6HBr.
But this is not the last way. There are two more. Obtaining selenic acid from selenium is possible due to its reaction with hydrogen peroxide. It looks like this: SeO 3 + H 2 O 2 → H 2 SeO 4.
Application
Now we can talk about him. Why is it important to obtain selenic acid? Because without it, the synthesis of its salts is impossible. They are better known as selenates. They will be discussed a little later.
The use of selenic acid as an oxidizing agent is very common, since it exhibits much more properties in this process than sulfuric acid. Even if it is diluted. If for sulfuric acid the electrode potentials are approximately ~0.169 V, then for selenium this indicator reaches ~1.147 V. And the difference will be noticed by every person who does not even understand chemistry.
Needless to say, if selenic acid easily oxidizes hydrochloric acid, and also dissolves gold, as a result of which selenate of this metal is formed, which is a red-yellow liquid.
ammonium selenate
The formula of this salt is (NH 4) 2SeO 4 . This substance is represented by colorless crystals. They dissolve well in water, but not in acetone or ethanol. They exhibit the general properties of salts.
They are used as insecticides. This is the name of the substances used to kill insects. Ammonium selenate is actively used in pest control. But it must be used with extreme caution, since this substance is especially toxic. But that's why it's effective.
barium selenate
Its formula is BaSeO 4 . This salt, unlike the previous one, does not dissolve in water. But on the other hand, it reacts with as a result of which selenium and barium sulfate are formed. Here it is of particular interest. After all, barium sulfate is an X-ray positive substance that is actively used in radiology.
This compound is non-toxic. It increases the contrast of the image obtained during the x-ray. Sulfate is not absorbed from the digestive tract and does not enter the bloodstream. It is excreted in the stool, so it is harmless to humans. This substance is used in the form of a suspension inside, together with sodium citrate and sorbitol.
beryllium selenate
This salt with the formula BeSeO 4 forms crystalline hydrates. The substance itself is formed in a very interesting way. It is the result of amphoteric beryllium hydroxide in selenic acid. Dissociation results in the formation of colorless crystals, which decompose when heated.
Where are the notorious hydroxides used? Usually they are used as raw materials to obtain beryllium. Or used as a catalyst for polymerization and Friedel-Crafts reactions.
Gold selenate
This substance has the following formula - Au 2 (SeO 4) 3. It looks like small yellow crystals. Naturally, this "salt" does not dissolve in water. It can only be affected by hot concentrated selenic acid. Selenium oxide is not formed as a result of this reaction, but a reddish-yellow solution will appear.
The "golden" salt is also soluble in nitric and sulfuric acids. But hydrogen chloride can destroy it.
Obtaining gold selenate is quite fast and simple. A temperature of 230 °C is sufficient for the reaction to take place.
copper selenate
The formula of this salt looks like this - CuSeO 4. This substance is white, soluble in water (but not in ethanol) crystals, which also form crystalline hydrates.
This salt is obtained according to the following formula: CuO + H2SeO 4 → 40-50 ° C CuSeO 4 + H 2 O. This reflects the dissolution of the oxide in selenic acid, as a result of which water is also released. By the way, the resulting crystalline hydrates subsequently lose part of H 2 O. To do this, it is enough to increase the temperature to 110 ° C. And if it is above 350 ° C, then the crystalline hydrate will begin to decompose altogether.
sodium selenate
This is the last salt in the formation of which the discussed acid is involved. Its formula is Na 2 SeO 4 . This compound is of particular interest because it is the result of the interaction of an alkali metal and a strong acid. Salt, by the way, is soluble in water, and also forms a crystalline hydrate.
They get it in different ways. The most common involves dissolving selenium in hydrogen peroxide. According to the formula, it looks like this: Se + 2NaOH + 3H 2 O 2 → Na 2 SeO 4 + 4H 2 O.
They also resort to the oxidation of sodium selenite, performed using hydrogen peroxide, electrolysis or oxygen. But the simplest method involves the interaction of the discussed acid with sodium carbonate. It is sometimes replaced with hydroxide.
This is perhaps the most actively used selenate. It is used as a medicine. According to the ATC, sodium selenate is a mineral supplement. However, neither in the USA nor in Russia, not a single medicine with its content is registered. But in Latvia and Denmark there are such drugs. The same "Bio-Selenium + Zinc", for example. An excellent tool for strengthening the immune system.
But selenate is included in the composition of biological additives sold in Russia. The same "Supradin Kids Junior" contains it in the amount of 12.5 mcg per tablet.
In general, it is through the use of this substance that doctors recommend treating selenium deficiency in the body. But, of course, before use, it is necessary to undergo a medical examination and consultation.
As you can see, even if selenic acid is not used in its pure form, the importance of its derivatives in chemistry, medicine and industry is obvious.
