Hydrochloric acid is a solution of gaseous hydrogen chloride HCl in water. The latter is a hygroscopic colorless gas with a pungent odor. Commonly consumed concentrated hydrochloric acid contains 36-38% hydrogen chloride and has a density 1.19 g/cm3. Such an acid smokes in air, since gaseous HCl; when combined with air moisture, tiny droplets of hydrochloric acid are formed.
Pure acid is colorless, while technical acid has a yellowish tint caused by traces of compounds of iron, chlorine and other elements ( FeCl 3 ).
Often a dilute acid containing 10% and less hydrogen chloride. Dilute solutions do not emit gaseous HCl and do not smoke in dry or humid air.
Hydrochloric acid is a volatile compound, as it evaporates when heated. It is a strong acid and reacts vigorously with most metals. However, metals such as gold, platinum, silver, tungsten and lead , hydrochloric acid is practically not etched. Many base metals, when dissolved in acid, form chlorides, for example zinc :
Zn + 2HCl \u003d ZnCl 2 + H 2.
Hydrochloric acid is widely used in industry for extracting metals from ores, pickling metals, etc. It is also used in the manufacture of soldering liquid, in the deposition silver and as part of royal vodka.
The scale of the use of hydrochloric acid in industry is less than nitric . This is due to the fact that hydrochloric acid causes corrosion of steel equipment. In addition, its volatile vapors are quite harmful and also cause corrosion of metal products. This must be taken into account when storing hydrochloric acid. Hydrochloric acid is stored and transported in rubber-lined tanks and barrels, i.e. in vessels, the inner surface of which is covered with acid-resistant rubber, as well as in glass bottles and polyethylene utensils.
Hydrochloric acid is used to produce chlorides zinc, manganese , iron and other metals, as well as ammonium chloride. Hydrochloric acid is used to clean the surfaces of metals, vessels, wells from carbonates, oxides and other sediments and contaminants. In this case, special additives are used - inhibitors that protect the metal from dissolution and corrosion, but do not delay the dissolution of oxides, carbonates and other similar compounds.
HCl used in the industrial production of synthetic resins, rubbers. It is used as a raw material in the production of methyl chloride from methyl alcohol, ethyl chloride from ethylene, and vinyl chloride from acetylene.
HCl poisonous. Poisoning usually occurs by mist formed when the gas interacts with water vapor in the air. HCl it is also absorbed on the mucous membranes with the formation of an acid that causes severe irritation. During prolonged work in the atmosphere HCl there are catarrhs of the respiratory tract, tooth decay, ulceration of the nasal mucosa, gastrointestinal disorders. Permissible content HCl in the air of working premises, no more 0 , 005 mg/l. For protection use a gas mask, goggles, rubber gloves, shoes, apron.
At the same time, our digestion is impossible without hydrochloric acid, its concentration in gastric juice is quite high. If the acidity in the body is lowered, then digestion is disturbed, and doctors prescribe such patients to take hydrochloric acid before eating.
Hydrochloric acid is one of the most powerful and dangerous substances for humans on the list of AHOV. However, it is surprising that it exists in the body of every person: hydrochloric acid is an integral part of gastric juice and plays an important role in the digestive process. In an amount of 0.2%, it promotes the transfer of food masses from the stomach to the duodenum and neutralizes microbes that enter the stomach from the external environment. It also activates the enzyme pepsinogen, is involved in the formation of secretin and some other hormones that stimulate the activity of the pancreas. For this purpose, it is used in medicine, prescribing its solution to patients to increase the acidity of gastric juice. In general, hydrochloric acid has a wide range of uses in our lives. For example, in heavy industry - to obtain chlorides of various metals, in the textile industry - to obtain synthetic dyes; for the food industry, acetic acid is made from it, for the pharmaceutical industry - activated carbon. It is also found in various adhesives and hydrolysis alcohol. It is used for etching metals, cleaning various vessels, casing pipes of boreholes from carbonates, oxides and other sediments and contaminants. In metallurgy, ores are treated with hydrochloric acid; in the leather industry, leather is treated before tanning and dyeing. Hydrochloric acid is transported in glass bottles or gummed (coated with a layer of rubber) metal vessels, as well as in plastic containers.
What is it as a chemical substance?
Hydrochloric acid, or hydrochloric acid, is an aqueous solution of hydrogen chloride HCl, which is a clear, colorless liquid with a pungent odor of hydrogen chloride. The technical variety of acid has a yellowish-green color due to impurities of chlorine and iron salts. The maximum concentration of hydrochloric acid is about 36% HCl; such a solution has a density of 1.18 g/cm3. Concentrated acid "smokes" in air, since the escaping gaseous HCl forms tiny droplets of hydrochloric acid with water vapor.
Despite this characteristic, hydrochloric acid is neither flammable nor explosive when exposed to air. But at the same time, it is one of the strongest acids and dissolves (with the release of hydrogen and the formation of salts - chlorides) all metals in the series of voltages up to hydrogen. Chlorides are also formed by the interaction of hydrochloric acid with metal oxides and hydroxides. With strong oxidizing agents, it behaves like a reducing agent.
Salts of hydrochloric acid are chlorides and, with the exception of AgCl, Hg2Cl2, are highly soluble in water. Materials such as glass, ceramics, porcelain, graphite, and fluoroplastic are resistant to hydrochloric acid.
Hydrochloric hydrogen chloride is obtained in water, which, in turn, is either directly synthesized from hydrogen and chlorine, or obtained by the action of sulfuric acid on sodium chloride.
Commercially available (technical) hydrochloric acid has a strength of at least 31% HCl (synthetic) and 27.5% HCl (from NaCI). Commercial acid is called concentrated if it contains 24% or more HCl; if the HCl content is less, then the acid is called dilute.
Hydrochloric acid - (hydrochloric acid, an aqueous solution of hydrogen chloride), known as the formula HCl, is a caustic chemical compound. Since ancient times, people have used this colorless liquid for various purposes, emitting a light smoke in the open air.
Properties of a chemical compound
HCl is used in various fields of human activity. It dissolves metals and their oxides, is absorbed in benzene, ether and water, does not destroy fluoroplastic, glass, ceramics and graphite. Its safe use is possible when stored and operated under the correct conditions, with all safety precautions observed.
Chemically pure (chemically pure) hydrochloric acid is formed during gaseous synthesis from chlorine and hydrogen, giving hydrogen chloride. It is absorbed in water, obtaining a solution with an HCl content of 38-39% at +18 C. An aqueous solution of hydrogen chloride is used in various fields of human activity. The price of chemically pure hydrochloric acid is variable, and depends on many components.
Scope of application of an aqueous solution of hydrogen chloride
The use of hydrochloric acid has become widespread due to its chemical and physical properties:
- in metallurgy, in the production of manganese, iron and zinc, in technological processes, in metal refining;
- in galvanoplasty - during etching and pickling;
- in the production of soda water to regulate acidity, in the manufacture of alcoholic beverages and syrups in the food industry;
- for leather processing in light industry;
- when treating non-potable water;
- for optimization of oil wells in the oil industry;
- in radio engineering and electronics.
Hydrochloric acid (HCl) in medicine
The most famous property of a hydrochloric acid solution is the alignment of the acid-base balance in the human body. A weak solution, or drugs, treats low acidity of the stomach. This optimizes the digestion of food, helps fight germs and bacteria that enter from the outside. Chemically pure hydrochloric acid helps to normalize the low level of gastric acidity and optimizes the digestion of proteins.
Oncology uses HCl to treat neoplasms and slow their progression. Hydrochloric acid preparations are prescribed for the prevention of stomach cancer, rheumatoid arthritis, diabetes, asthma, urticaria, cholelithiasis and others. In folk medicine, hemorrhoids are treated with a weak acid solution.
You can learn more about the properties and types of hydrochloric acid.
Receipt. Hydrochloric acid is produced by dissolving hydrogen chloride in water.
Pay attention to the device shown in the figure on the left. It is used to produce hydrochloric acid. During the process of obtaining hydrochloric acid, monitor the gas outlet tube, it should be near the water level, and not be immersed in it. If this is not followed, then due to the high solubility of hydrogen chloride, water will enter the test tube with sulfuric acid and an explosion may occur.
In industry, hydrochloric acid is usually produced by burning hydrogen in chlorine and dissolving the reaction product in water.
physical properties. By dissolving hydrogen chloride in water, even a 40% hydrochloric acid solution with a density of 1.19 g/cm 3 can be obtained. However, commercially available concentrated hydrochloric acid contains about 0.37 mass fractions, or about 37% hydrogen chloride. The density of this solution is approximately 1.19 g/cm 3 . When an acid is diluted, the density of its solution decreases.
Concentrated hydrochloric acid is an invaluable solution, highly fuming in moist air, with a pungent odor due to the release of hydrogen chloride.
Chemical properties. Hydrochloric acid has a number of common properties that are characteristic of most acids. In addition, it has some specific properties.
Properties of HCL in common with other acids: 1) Color change of indicators 2) interaction with metals 2HCL + Zn → ZnCL 2 + H 2 3) Interaction with basic and amphoteric oxides: 2HCL + CaO → CaCl 2 + H 2 O; 2HCL + ZnO → ZnHCL 2 + H 2 O 4) Interaction with bases: 2HCL + Cu (OH) 2 → CuCl 2 + 2H 2 O 5) Interaction with salts: 2HCL + CaCO 3 → H 2 O + CO 2 + CaCL 2
Specific properties of HCL: 1) Interaction with silver nitrate (silver nitrate is a reagent for hydrochloric acid and its salts); a white precipitate will form, which does not dissolve in water or acids: HCL + AgNO3 → AgCL↓ + HNO 3 2O+3CL2
Application. A huge amount of hydrochloric acid is consumed to remove iron oxides before coating products from this metal with other metals (tin, chromium, nickel). In order for hydrochloric acid to react only with oxides, but not with metal, special substances are added to it, which are called inhibitors. Inhibitors- Substances that slow down reactions.
Hydrochloric acid is used to obtain various chlorides. It is used to produce chlorine. Very often, a solution of hydrochloric acid is prescribed to patients with low acidity of gastric juice. Hydrochloric acid is found in everyone in the body, it is part of the gastric juice, which is necessary for digestion.
In the food industry, hydrochloric acid is used only in the form of a solution. It is used to regulate acidity in the production of citric acid, gelatin or fructose (E 507).
Do not forget that hydrochloric acid is dangerous for the skin. It poses an even greater danger to the eyes. Influencing a person, it can cause tooth decay, irritation of mucous membranes, and suffocation.
In addition, hydrochloric acid is actively used in electroplating and hydrometallurgy (scale removal, rust removal, leather treatment, chemical reagents, as a rock solvent in oil production, in the production of rubbers, sodium glutamate, soda, Cl 2). Hydrochloric acid is used for the regeneration of Cl 2 in organic synthesis (to obtain vinyl chloride, alkyl chlorides, etc.) It can be used as a catalyst in the production of diphenylolpropane, benzene alkylation.
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approximate solutions. In most cases, the laboratory has to use hydrochloric, sulfuric and nitric acids. Acids are commercially available in the form of concentrated solutions, the percentage of which is determined by their density.
The acids used in the laboratory are technical and pure. Technical acids contain impurities, and therefore are not used in analytical work.
Concentrated hydrochloric acid smokes in air, so you need to work with it in a fume hood. The most concentrated hydrochloric acid has a density of 1.2 g/cm3 and contains 39.11% hydrogen chloride.
Dilution of the acid is carried out according to the calculation described above.
Example. It is necessary to prepare 1 liter of a 5% solution of hydrochloric acid, using its solution with a density of 1.19 g / cm3. According to the reference book, we learn that a 5% solution has a density of 1.024 g / cm3; therefore, 1 liter of it will weigh 1.024 * 1000 \u003d 1024 g. This amount should contain pure hydrogen chloride:
Acid with a density of 1.19 g/cm3 contains 37.23% HCl (we also find it in the reference book). To find out how much this acid should be taken, make up the proportion:
or 137.5 / 1.19 \u003d 115.5 acids with a density of 1.19 g / cm3. Having measured 116 ml of an acid solution, bring its volume to 1 liter.
Sulfuric acid is also diluted. When diluting it, remember that you need to add acid to water ~, and not vice versa. When diluted, strong heating occurs, and if water is added to the acid, then splashing is possible, which is dangerous, since sulfuric acid causes severe burns. If acid gets on clothes or shoes, quickly wash the spilled area with plenty of water, and then neutralize the acid with sodium carbonate or ammonia solution. In case of contact with the skin of the hands or face, immediately wash the area with plenty of water.
Special care must be taken when handling oleum, which is sulfuric acid monohydrate saturated with sulfuric anhydride SO3. According to the content of the latter, oleum can be of several concentrations.
It should be remembered that with a slight cooling, the oleum crystallizes and is in a liquid state only at room temperature. In air, it smokes with the release of SO3, which forms sulfuric acid vapors when interacting with air moisture.
Great difficulties are caused by the transfusion of oleum from a large container into a small one. This operation should be carried out either under draft or in air, but where the resulting sulfuric acid and SO3 cannot have any harmful effect on people and surrounding objects.
If the oleum has hardened, it should first be heated by placing the container with it in a warm room. When the oleum melts and turns into an oily liquid, it must be taken out into the air and poured into smaller dishes, using the method of squeezing with the help of air (dry) or an inert gas (nitrogen).
When mixed with water, nitric acid also heats up (although not as strong as in the case of sulfuric acid), and therefore precautions must be taken when working with it.
In laboratory practice, solid organic acids are used. Handling them is much easier and more convenient than liquid ones. In this case, care should only be taken to ensure that the acids are not contaminated by anything foreign. If necessary, solid organic acids are purified by recrystallization (see Ch. 15 "Crystallization"),
precise solutions. Accurate acid solutions they are prepared in the same way as the approximate ones, with the only difference that at first they strive to obtain a solution of a slightly higher concentration, so that after that it can be diluted accurately, according to calculation. For precise solutions, only chemically pure preparations are taken.
The required amount of concentrated acids is usually taken by volume, calculated from the density.
Example. It is necessary to prepare 0.1 and. H2SO4 solution. This means that 1 liter of solution should contain:
Acid with a density of 1.84 g / cmg contains 95.6% H2SO4 n for the preparation of 1 l of 0.1 n. solution, you need to take the following amount (x) of it (in g):
The corresponding volume of acid will be:
Having measured exactly 2.8 ml of acid from a burette, dilute it to 1 liter in a volumetric flask and then titrate with an alkali solution and establish the normality of the resulting solution. If the solution turns out to be more concentrated), the calculated amount of water is added to it from the burette. For example, during titration, it was found that 1 ml of 6.1 N. H2SO4 solution contains not 0.0049 g H2SO4, but 0.0051 g. To calculate the amount of water that is needed to prepare exactly 0.1 N. solution, make up the proportion:
The calculation shows that this volume is equal to 1041 ml. the solution must be added 1041 - 1000 = 41 ml of water. It should also take into account the amount of solution that is taken for titration. Let 20 ml be taken, which is 20/1000 = 0.02 of the available volume. Therefore, water should be added not 41 ml, but less: 41 - (41 * 0.02) \u003d \u003d 41 -0.8 \u003d 40.2 ml.
* To measure acid, use a carefully dried burette with a ground stopcock. .
The corrected solution should be checked again for the content of the substance taken for dissolution. Accurate solutions of hydrochloric acid are also prepared by the ion-exchange method, based on the exact calculated sample of sodium chloride. The sample calculated and weighed on an analytical balance is dissolved in distilled or demineralized water, the resulting solution is passed through a chromatographic column filled with a cation exchanger in the H-form. The solution flowing from the column will contain an equivalent amount of HCl.
As a rule, exact (or titrated) solutions should be stored in tightly closed flasks. It is imperative to insert a calcium chloride tube into the cork of the vessel, filled in the case of an alkali solution with soda lime or ascarite, and in the case of an acid, with calcium chloride or simply cotton wool.
To check the normality of acids, calcined sodium carbonate Na2COs is often used. However, it is hygroscopic and therefore does not fully meet the requirements of analysts. It is much more convenient to use for these purposes acidic potassium carbonate KHCO3, dried in a desiccator over CaCl2.
When titrating, it is useful to use a “witness”, for the preparation of which one drop of acid (if titrating alkali) or alkali (if titrating acid) and as many drops of an indicator solution as added to the titrated solution are added to distilled or demineralized water.
The preparation of empirical, according to the substance being determined, and standard solutions, acids is carried out according to the calculation using the formulas given for these and the cases described above.
