Hydrogen chloride is a gas about 1.3 times heavier than air. It is colorless, but with a sharp, suffocating and characteristic odor. At a temperature of minus 84C, hydrogen chloride passes from a gaseous to a liquid state, and at minus 112C it solidifies. Hydrogen chloride dissolves in water. One liter of H2O can absorb up to 500 ml of gas. Its solution is called hydrochloric or hydrochloric acid. Concentrated hydrochloric acid at 20C is characterized by the maximum possible basic substance, equal to 38%. The solution is a strong monobasic acid (it smokes in air, and forms an acid mist in the presence of moisture), it also has other names: hydrochloric acid, and according to Ukrainian nomenclature - chloride acid. The chemical formula can be represented as follows: HCl. The molar mass is 36.5 g/mol. The density of concentrated hydrochloric acid at 20C is 1.19 g/cm³. This is harmful substance, which belongs to the second class of danger.
In a "dry" form, hydrogen chloride cannot interact even with active metals, but in the presence of moisture, the reaction proceeds quite vigorously. This strong hydrochloric acid is capable of reacting with all metals that are to the left of hydrogen in the voltage series. In addition, it interacts with basic and amphoteric oxides, bases, and also with salts:
- Fe + 2HCl → FeCl2 + H2;
- 2HCl + CuO → CuCl2 + H2O;
- 3HCl + Fe(OH)3 → FeCl3 + 3H2O;
- 2HCl + Na2CO3 → 2NaCl + H2O + CO2;
- HCl + AgNO3 → AgCl↓ + HNO3.
In addition to the general properties characteristic of each strong acid, concentrated hydrochloric acid reacts with various oxidizing agents, releasing free chlorine. Salts of this acid are called chlorides. Almost all of them dissolve well in water and completely dissociate into ions. Slightly soluble are: lead chloride PbCl2, silver chloride AgCl, monovalent mercury chloride Hg2Cl2 (calomel) and monovalent copper chloride CuCl. Hydrogen chloride is capable of entering into an addition reaction to a double or triple bond, with the formation of chlorine derivatives of organic compounds.
Under laboratory conditions, hydrogen chloride is obtained by exposure to dry concentrated sulfuric acid. Reaction in different conditions can proceed with the formation of sodium salts (acidic or medium):
- H2SO4 + NaCl → NaHSO4 + HCl
- H2SO4 + 2NaCl → Na2SO4 + 2HCl.
The first reaction goes to completion at low heating, the second - at higher temperatures. Therefore, in the laboratory, it is better to obtain hydrogen chloride by the first method, for which the amount of sulfuric acid is recommended to be taken from the calculation of obtaining the acid salt NaHSO4. Then, by dissolving hydrogen chloride in water, hydrochloric acid is obtained. In industry, it is obtained by burning hydrogen in an atmosphere of chlorine or by acting on dry sodium chloride (only the second with concentrated sulfuric acid. Hydrogen chloride is also obtained as a by-product during the chlorination of saturated organic compounds. In industry, hydrogen chloride obtained by one of the above methods is dissolved in special towers in which liquid is passed from top to bottom, and gas is supplied from bottom to top, that is, according to the principle of counterflow.
Hydrochloric acid is transported in special rubberized tanks or containers, as well as in polyethylene barrels with a capacity of 50 liters or glass bottles with a capacity of 20 liters. When there is a risk of formation of explosive hydrogen-air mixtures. Therefore, the contact of the hydrogen formed as a result of the reaction with air, as well as (with the help of anti-corrosion coatings) the contact of acid with metals, must be completely excluded. Before removing the apparatus and pipelines, where it was stored or transported, for repair, it is necessary to carry out nitrogen purges and control the state of the gas phase.
Hydrogen chloride is widely used in industrial production and in laboratory practice. It is used to obtain salts and as a reagent in analytical studies. Technical hydrochloric acid is produced in accordance with GOST 857-95 (the text is identical international standard ISO 905-78), reagent - according to GOST 3118-77. The concentration of the technical product depends on the brand and grade and can be 31.5%, 33% or 35%, and externally the product is yellowish in color due to the content of impurities of iron, chlorine and other chemicals. The reactive acid should be a colorless and transparent liquid with a mass fraction of 35 to 38%.
Definition and formula of hydrochloric acid
DEFINITION
Hydrochloric acid (hydrochloric acid, hydrochloric acid, hydrogen chloride) is a solution of hydrogen chloride \(\\mathrm(HCl)\) in water.
Hydrochloric acid formula
Formula - \(\ \mathrm(HCl) \)
The molar mass is 36.46 g/mol.
Physical properties - colorless caustic liquid, "smokes" in air.
Technical hydrochloric acid has a yellow color due to the presence of impurities of iron, chlorine and other substances.
The maximum concentration in the solution at \(\ 20^(\circ) \mathrm(C) \) is 38%, the density of this solution is 1.19 g/cm3. Molar mass 36.46 g/mol.
Hydrochloric acid is a strong monobasic acid, dissociation constant.
Forms salts - chlorides.
Chemical properties of hydrochloric acid
It interacts with metals that are in the electrochemical series of voltages up to hydrogen with the formation of the corresponding chlorides and the release of hydrogen:
\(\ Z n+2 H C l=Z n C l_(2)+H_(2) \uparrow \)
Interacts with metal oxides to form soluble salts and water:
\(\ M g O+2 H C l=M g C l_(2)+H_(2) O \)
Reacts with metal hydroxides to form soluble chlorides and water:
\(\ A l(O H)_(3)+3 H C l=A l C l_(3)+3 H_(2) O \)
Interacts with metal salts formed by weaker acids:
\(\ \mathrm(Na)_(2) \mathrm(CO)_(3)+2 \mathrm(HCl)=2 \mathrm(NaCl)+\mathrm(H)_(2) \mathrm(O) +\mathrm(CO)_(2) \uparrow \)
Reacts with strong oxidants (potassium permanganate, manganese dioxide) to release chlorine:
\(\ 2 K M n O_(4)+16 H C l=5 C l_(2) \uparrow+2 M n C l_(2)+2 K C l+8 H_(2) O \)
Reacts with ammonia to form thick white smoke consisting of tiny crystals of ammonium chloride:
\(\ N H_(3)+H C l=N H_(4) C l \)
A qualitative reaction to hydrochloric acid and its salts is a reaction with silver nitrate, which results in the formation of a white curd precipitate of silver chloride, insoluble in nitric acid:
\(\ H C l+A g N O_(3)=A g C l \downarrow+H N O_(3) \)
Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water.
Application
Hydrochloric acid is used in hydrometallurgy and electroforming (etching, pickling), to clean the surface of metals during soldering and tinning, to obtain metal chlorides (zinc, manganese, iron, etc.). Mixtures of hydrochloric acid with surfactants are used to clean ceramic and metal products from contamination and disinfection.
In the food industry, hydrochloric acid is used as an acidity regulator \(\\mathrm(pH)\) , food additive E507. Is natural integral part human gastric juice.
Concentrated hydrochloric acid is a corrosive substance that causes severe chemical burns if it comes into contact with the skin. Acid in the eyes is especially dangerous. To neutralize burns, a solution of weak alkali (baking soda) is used.
Examples of problem solving
Calculate the normality of a hydrochloric acid solution if 19.2 ml of a 0.1 N sodium hydroxide solution was used to titrate 20 ml of it.
We write the equation for the titration reaction:
\(\ H C l+N a O H=N a C l+H_(2) O \)
Let us write down the law of equivalents for the given titration process:
\(\ V_(N a O H) \cdot N_(N a O H)=V_(H C l) \cdot N_(H C l) \)
We express the normal concentration of a hydrochloric acid solution:
\(\ N_(H C l)=\frac(V_(N a O H) \cdot N_(N a O H))(V_(H C l))=\frac(19,2 \cdot 0,1)(20) \u003d 0.096 \)
The normality of a hydrochloric acid solution is 0.096 N.
A solution of hydrochloric acid \ (\ \mathrm (HCl) \) with a volume of 1.8 ml (density 1.18 g / ml) with a mass fraction of a substance of 36% was diluted with water to 1 liter. Find \(\ _(1) \mathrm(pH) \) of the resulting solution.
We write the equation for the dissociation of hydrochloric acid:
\(\ H C l=H^(+)+C l^(-) \)
Let's find the mass of the initial solution of hydrochloric acid by the formula:
\(\ m=\rho \cdot V\)
where \(\ \rho \) is the density of the solution, \(\ \mathrm(V) \) is the volume of the solution.
\(\ m_(p-p a)=1.18 \cdot 1.8=2.124 g.\)
Find the mass of hydrochloric acid in solution. The expression for the mass fraction of a substance in solution:
\(\ \omega=\frac(m_(b-b a))(m_(p-p a)) \)
If the hydrochloric acid solution is 36%, then the mass fraction of hydrochloric acid in it will be equal to 0.36.
Express the mass of hydrochloric acid:
\(\ m_(H C l)=\omega \cdot m_(p-p a)=0.36 \cdot 2.124=0.765 \)
Given that the molar mass of hydrochloric acid is 36.5 g/mol, we calculate the amount of substance \(\ \mathrm(HCl) \) in solution
\(\ n_(H C l)=\frac(m_(H C l))(M_(H C l))=\frac(0.765)(36.5)=0.021 \) mol
Since the initial volume of the solution was diluted with water to 1 liter, we find the molar concentration of the resulting hydrochloric acid solution using the formula:
\(\ C_(M)(H C l)=\frac(n_(H C l))(V)=\frac(0.021)(1)=0.021 \) mol/l
Hydrochloric acid is a strong acid, it dissociates completely in an aqueous solution, so the concentration of hydrogen ions will be equal to the concentration of the acid:
\(\ \left \u003d M (H C l) \u003d 0.021 \) mol / l
The pH of the solution is calculated by the formula:
\(\ p H=-l g\left=-\lg (0.021)=1.678=1.678 \)
The pH of the resulting solution is 1.678
1.2679; G crnt 51.4°C, p crit 8.258 MPa, d crit 0.42 g/cm 3 ; -92.31 kJ / mol, D H pl 1.9924 kJ / mol (-114.22 ° C), D H test 16.1421 kJ / mol (-8.05 ° C); 186.79 J / (mol ) TO); vapor pressure (Pa): 133.32 10 -6 (-200.7 ° C), 2.775 10 3 (-130.15 ° C), 10.0 10 4 (-85.1 ° C), 74.0 10 4 (-40 ° C), 24.95 10 5 (O ° C), 76.9 10 5 (50 ° C); ur-tion temperature dependence steam pressure lgp (kPa) = -905.53 / T + 1.75lgT- -500.77 10 -5 T + 3.78229 (160-260 K); coefficient compressibility 0.00787; g 23 mN/cm (-155°C); r 0.29 10 7 Ohm m (-85°C), 0.59 10 7 (-114.22°C). See also table. one.
Solubility of HCl in hydrocarbons at 25 °C and 0.1 MPa (mol.%): in pentane-0.47, hexane-1.12, heptane-1.47, octane-1.63. The p-value of HC1 in alkyl and aryl halides is low, for example. 0.07 mol / mol for C 4 H 9 C1. P-value in the range from -20 to 60 ° C decreases in the series dichloroethane-tri-chloroethane-tetrachloroethane-trichlorethylene. P-value at 10 ° C in a number of alcohols is approximately 1 mol / mol of alcohol, in carboxylic esters to-t 0.6 mol / mol, in carboxylic acids 0.2 mol / mol. In simple ethers, stable adducts R 2 O HCl are formed. The p-value of HC1 in chloride melts obeys Henry's law and amounts to 2.51 10 -4 (800 ° C), 1.75 10 -4 mol / mol (900 ° C) for KCl, 1.90 10 for NaCl -4 mol / mol (900 ° C).
Salt to-ta. The dissolution of HCl in water is highly exothermic. process, for infinitely razb. water solution D H 0 dissolution of HCl -69.9 kJ / mol, Cl ion -- 167.080 kJ/mol; HC1 in water is completely ionized. The p-value of HC1 in water depends on the temperature (Table 2) and the partial pressure of HC1 in the gas mixture. Density of hydrochloric acid decomp. concentrations and h at 20 °C are presented in Table. 3 and 4. With an increase in the temperature h of hydrochloric acid decreases, for example: for 23.05% hydrochloric acid at 25 ° C h 1364 mPa s, at 35 ° C 1.170 mPa s. hydrochloric acid containing h moles water per 1 mole of HC1 is [kJ/(kg K)]: 3.136 (n = 10), 3.580 (n = 20), 3.902 (n = 50), 4.036 (n = 100), 4.061 (n = 200 ).
HCl forms an azeotropic mixture with water (Table 5). In the HCl-water system, there are three eutectic. points: - 74.7 ° C (23.0% by mass of HCl); -73.0°C (26.5% HCl); -87.5°C (24.8% HC1, metastable phase). Known crystalline hydrates Hcl nH 2 O, where n = 8.6 (mp. -40 ° C), 4. 3 (mp. -24.4 ° C), 2 (mp. -17, 7°C) and 1 (mp. -15.35°C). Ice crystallizes from 10% hydrochloric acid at -20, from 15% at -30, from 20% at -60 and from 24% at -80°C. The p-value of metal halides decreases with an increase in the concentration of HCl in hydrochloric acid, which is used to salt them out.
Chemical properties. Pure dry HCl begins to dissociate above 1500°C, it is chemically passive. Mn. metals, C, S, P do not interact. even with liquid HCl. It reacts with nitrides, carbides, borides, sulfides above 650 ° C, with hydrides Si, Ge and B-in are present. AlCl 3, with oxides of transition metals - at 300 ° C and above. O 2 and HNO 3 are oxidized to Cl 2, with SO 3 gives C1SO 3 H. O p-tions with org. compounds, see Hydrohalogenation.
With hydrochloric acid is chemically very active. Dissolves with the release of H 2 all metals having negative. normal potential,with me. metal oxides and hydroxides forms chlorides, releases free. to-you from such salts as phosphates, silicates, borates, etc.
Receipt. In the industry, Hcl get a trace. ways-sulfate, synthetic. and from off-gases (side gases) of a number of processes. The first two methods lose their meaning. So, in the USA in 1965 the share of waste hydrochloric acid was 77.6% in the total volume of production, and in 1982-94%.
The production of hydrochloric acid (reactive, obtained by the sulfate method, synthetic, off-gas) consists in obtaining HCl with the last. its absorption by water. Depending on the method of removing the heat of absorption (reaches 72.8 kJ / mol), the processes are divided into isothermal, adiabatic. and combined.
The sulfate method is based on the interaction. NaCl with conc. H 2 SO 4 at 500-550 ° C. reaction gases contain from 50-65% HCl (muffle furnaces) to 5% HCl (fluidized bed reactor). It is proposed to replace H 2 SO 4 with a mixture of SO 2 and O 2 (process temperature approx. 540 ° C, cat.-Fe 2 O 3).
The basis of the direct synthesis of HCl is the chain burning p-tion: H 2 + Cl 2 2HCl + 184.7 kJ. The equilibrium constant K p is calculated from the equation: lgK p \u003d 9554 / T- 0.5331g T + 2.42.
R-tion is initiated by light, moisture, porous solids (charcoal, porous Pt) and some minerals. in-you (quartz, clay). Synthesis is carried out with an excess of H 2 (5-10%) in combustion chambers made of steel, graphite, quartz, refractory bricks. Naib. modern HCl pollution prevention material - graphite impregnated with phenol-formald. resins. To prevent the explosive nature of combustion, the reagents are mixed directly in the flame of the burner. To the top. heat exchangers are installed in the zone of combustion chambers to cool the reaction. gases up to 150-160°С. The power of modern graphite furnaces reaches 65 tons / day (in terms of 35% hydrochloric acid). In case of H 2 deficiency, decomp. process modifications; for example, pass a mixture of Cl 2 with water vapor through a layer of porous hot coal:
2Cl 2 + 2H 2 O + C: 4HCl + CO 2 + 288.9 kJ
The temperature of the process (1000-1600 ° C) depends on the type of coal and the presence of impurities in it that are catalysts (eg, Fe 2 O 3). It is promising to use a mixture of CO with water vapor:
CO + H 2 O + Cl 2: 2HCl + CO 2
More than 90% of hydrochloric acid in developed countries is obtained from off-gas HCl, which is formed during chlorination and dehydrochlorination of org. compounds, pyrolysis chlororg. waste, metal chlorides, obtaining potassium non-chlorinated. fertilizers, etc. Abgases contain decomp. quantity of HC1, inert impurities (N 2, H 2, CH 4), slightly soluble in water org. in-va (chlorobenzene, chloromethanes), water-soluble in-va (acetic acid, chloral), acidic impurities (Cl 2, HF, O 2) and water. The use of isothermal absorption is advisable at a low content of HC1 in exhaust gases (but with a content of inert impurities less than 40%). Naib. film absorbers are promising, allowing to extract from 65 to 85% HCl from the initial off-gas.
Naib. adiabatic schemes are widely used. absorption. Abgases are introduced into the lower. part of the absorber, and water (or dilute hydrochloric acid) countercurrent to the top. Hydrochloric acid is heated to the boiling point due to the heat of dissolution of HCl. Change t-ry absorption and concentration of Hcl is given in fig. 1. The absorption temperature is determined by the boiling temperature of the corresponding concentration (max. boiling temperature of the azeotropic mixture is approx. 110 ° C).
On fig. 2 shows a typical adiabatic scheme. absorption of HCl from off-gases formed during chlorination (eg, obtaining chlorobenzene). HCl is absorbed in the absorber 1, and the remains of water-soluble org. in-in is separated from water after condensation in the apparatus 2, further purified in the tail column 4 and separators 3, 5 and commercial hydrochloric acid is obtained.
Rice. 1. Distribution scheme t-r (curve 1) and
Like acids. The education program provides for the memorization by students of the names and formulas of six representatives of this group. And, looking through the table provided by the textbook, you notice in the list of acids the one that comes first and interested you in the first place - hydrochloric acid. Alas, in the classroom at school, neither the property nor any other information about it is studied. Therefore, those who are eager to gain knowledge outside the school curriculum are looking for additional information in all sorts of sources. But often, many do not find the information they need. And so the topic of today's article is dedicated to this particular acid.
Definition
Hydrochloric acid is a strong monobasic acid. In some sources, it may be called hydrochloric and hydrochloric, as well as hydrogen chloride.
Physical propertiesIt is a colorless and fuming caustic liquid in the air (photo on the right). However, technical acid has a yellowish color due to the presence of iron, chlorine and other additives in it. Its largest concentration at a temperature of 20 ° C is 38%. The density of hydrochloric acid with such parameters is 1.19 g/cm 3 . But this compound in varying degrees of saturation has completely different data. With a decrease in concentration, the numerical value of molarity, viscosity and melting point decrease, but the specific heat capacity and boiling point increase. Solidification of hydrochloric acid of any concentration gives various crystalline hydrates.
Chemical properties
All metals that come before hydrogen in the electrochemical series of their voltage can interact with this compound, forming salts and releasing hydrogen gas. If they are replaced by metal oxides, then the reaction products will be soluble salt and water. The same effect will be in the interaction of hydrochloric acid with hydroxides. If, however, any salt of metals (for example, sodium carbonate) is added to it, the residue of which was taken from a weaker acid (carbonic), then chloride of this metal (sodium), water and gas corresponding to the acid residue (in this case, carbon dioxide) are formed. .
Receipt
The compound now discussed is formed when hydrogen chloride gas, which can be obtained by burning hydrogen in chlorine, is dissolved in water. Hydrochloric acid, which was obtained using this method, is called synthetic. Off-gases can also serve as a source for obtaining this substance. And such hydrochloric acid will be called off-gas. Recently, the level of production of hydrochloric acid using this method is much higher than its production by a synthetic method, although the latter gives the compound in a purer form. These are all ways of getting it in industry. However, in laboratories, hydrochloric acid is obtained in three ways (the first two differ only in temperature and reaction products) using various types of chemical interactions, such as:
- Effect of saturated sulfuric acid on sodium chloride at 150°C.
- The interaction of the above substances under conditions with a temperature of 550 ° C and above.
- Hydrolysis of aluminum or magnesium chlorides.
Hydrometallurgy and electroforming cannot do without the use of hydrochloric acid, where it is needed, in order to clean the surface of metals during tinning and soldering and to obtain chlorides of manganese, iron, zinc and other metals. In the food industry, this compound is known as food additive E507 - there it is an acidity regulator necessary in order to make seltzer (soda) water. Concentrated hydrochloric acid is also found in gastric juice any person and helps to digest food. During this process, its degree of saturation decreases, because. this composition is diluted with food. However, with prolonged fasting, the concentration of hydrochloric acid in the stomach gradually increases. And since this compound is very caustic, it can lead to stomach ulcers.
Conclusion
Hydrochloric acid can be both beneficial and harmful to humans. Its contact with the skin leads to the appearance of severe chemical burns, and the vapors of this compound irritate the respiratory tract and eyes. But if you handle this substance carefully, it can come in handy more than once in
Hydrochloric acid(hydrochloric acid) (Hydrochloric acid) - a solution of hydrogen chloride in water, a strong monobasic acid. Colorless, "fuming" in air, highly caustic liquid (technical hydrochloric acid is yellowish due to impurities of Fe, Cl2, etc.).
The maximum concentration at 20°C is 38% by mass, the density of such a solution is 1.19 g/cm3. Salts of hydrochloric acid are called chlorides.
Chemical formula: HCl
Molecular weight (according to international atomic masses 1985) - 36.46
Pure acid is colorless, while technical acid has a yellowish tint caused by traces of compounds of iron, chlorine and other elements (FeCl3).
Often a dilute acid containing 10% or less hydrogen chloride is used. Diluted 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 are practically not etched with hydrochloric acid. Many base metals, when dissolved in acid, form chlorides, such as zinc.
Physical properties of hydrochloric acid
Physical properties of hydrochloric acid at 20 °C, 1 atm (101 kPa)
| Conc. (the weight) c: kg HCl/kg |
Conc. (g/l) c: kg HCl/m3 |
Density ρ: kg/l |
Molarity M |
pH | Viscosity η: mPa∙s |
| 10% | 104,80 | 1,048 | 2.87M | -0,5 | 1,16 |
| 20% | 219,60 | 1,098 | 6.02M | -0,8 | 1,37 |
| 30% | 344,70 | 1,149 | 9.45M | -1,0 | 1,70 |
| 32% | 370,88 | 1,159 | 10.17M | -1,0 | 1,80 |
| 34% | 397,46 | 1,169 | 10.90M | -1,0 | 1,90 |
| 36% | 424,44 | 1,179 | 11.64M | -1,1 | 1,99 |
| 38% | 451,82 | 1,189 | 12.39M | -1,1 | 2,10 |
| Conc. (the weight) c: kg HCl/kg |
Specific heat capacity s: kJ/(kg∙K) |
Pressure pair PHCl: Pa |
Temperature boiling t°kip |
Temperature melting t°pl |
|
| 10% | 3,47 | 0,527 | 103°C | -18°C | |
| 20% | 2,99 | 27,3 | 108°C | -59°C | |
| 30% | 2,60 | 1,410 | 90°C | -52°C | |
| 32% | 2,55 | 3,130 | 84°C | -43°C | |
| 34% | 2,50 | 6,733 | 71°C | -36°C | |
| 36% | 2,46 | 14,100 | 61°C | -30°C | |
| 38% | 2,43 | 28,000 | 48°C | -26°C |
Chemical properties of hydrochloric acid
Hydrochloric acid is a typical monobasic acid. Hydrochloric acid reacts with the following substances:
- with metals standing in the electrochemical series of metals up to hydrogen;
- with oxides of all metals;
- with metal hydroxides;
- with metal salts formed by weaker acids.
Hydrochloric acid production
Hydrochloric acid is produced by dissolving hydrogen chloride gas in water.
In the industry, hydrochloric acid is produced by the following methods:
- sulfate - obtaining hydrogen chloride by the action of concentrated sulfuric acid on sodium chloride;
- synthetic - obtaining hydrogen chloride by burning hydrogen in chlorine;
- from off-gases (side gases) of a number of actions.
The first two methods are losing their industrial significance.
Over 90% of hydrochloric acid Currently, they are produced from off-gas hydrogen chloride HCI, which is formed during the chlorination and dehydrochlorination of organic compounds, pyrolysis of organochlorine wastes, metal chlorides, production of potash non-chlorinated fertilizers, etc.
