Hydrochloric Acid 1000ml 35%
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical.
Chemical properties
Gaseous hydrogen chloride is a molecular compound with a covalent bond between the hydrogen and chlorine atoms. In aqueous solutions dissociation is complete, with the formation of chloride ions and hydrated hydrogen ions (hydronium ions). A combined IR, Raman, X-ray, and neutron diffraction study of concentrated hydrochloric acid showed that the hydronium ion forms hydrogen bonded complexes with other water molecules.
The pKa value of hydrochloric acid in aqueous solution is estimated theoretically to be −5.9. A solution of hydrogen chloride in water behaves as a strong acid: the concentration of HCl molecules is effectively zero.
Physical properties
Mass fraction | Concentration | Density | Molarity | pH | Viscosity | Specific heat | Vapour pressure | Boiling point | Melting point | |
---|---|---|---|---|---|---|---|---|---|---|
kg HCl/kg | kg HCl/m3 | Baumé | kg/L | mol/L | mPa·s | kJ/(kg·K) | kPa | °C | °C | |
10% | 104.80 | 6.6 | 1.048 | 2.87 | −0.5 | 1.16 | 3.47 | 1.95 | 103 | −18 |
20% | 219.60 | 13 | 1.098 | 6.02 | −0.8 | 1.37 | 2.99 | 1.40 | 108 | −59 |
30% | 344.70 | 19 | 1.149 | 9.45 | −1.0 | 1.70 | 2.60 | 2.13 | 90 | −52 |
32% | 370.88 | 20 | 1.159 | 10.17 | −1.0 | 1.80 | 2.55 | 3.73 | 84 | −43 |
34% | 397.46 | 21 | 1.169 | 10.90 | −1.0 | 1.90 | 2.50 | 7.24 | 71 | −36 |
36% | 424.44 | 22 | 1.179 | 11.81 | −1.1 | 1.99 | 2.46 | 14.5 | 61 | −30 |
38% | 451.82 | 23 | 1.189 | 12.39 | −1.1 | 2.10 | 2.43 | 28.3 | 48 | −26 |
The reference temperature and pressure for the above table are 20 °C and 1 atmosphere (101.325 kPa). Vapour pressure values are taken from the International Critical Tables and refer to the total vapour pressure of the solution. |
Physical properties of hydrochloric acid, such as boiling and melting points, density, and pH, depend on the concentration or molarity of HCl in the aqueous solution. They range from those of water at very low concentrations approaching 0% HCl to values for fuming hydrochloric acid at over 40% HCl.
Hydrochloric acid as the binary (two-component) mixture of HCl and H2O has a constant-boiling azeotrope at 20.2% HCl and 108.6 °C (227 °F). There are four constant-crystallization eutectic points for hydrochloric acid, between the crystal form of [H3O]Cl (68% HCl), [H5O2]Cl (51% HCl), [H7O3]Cl (41% HCl), [H3O]Cl·5H2O (25% HCl), and ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the [H7O3]Cl crystallization. They are all Hydronium salts.
Production
Hydrochloric acid is usually prepared industrially by dissolving hydrogen chloride in water. Hydrogen chloride can be generated in many ways, and thus several precursors to hydrochloric acid exist. The large-scale production of hydrochloric acid is almost always integrated with the industrial scale production of other chemicals, such as in the chloralkali process which produces hydroxide, hydrogen, and chlorine, the latter of which can be combined to produce HCl.[29][30]
Hydrogen chloride is produced by combining chlorine and hydrogen:
- Cl2 + H2 → 2 HCl
As the reaction is exothermic, the installation is called an HCl oven or HCl burner. The resulting hydrogen chloride gas is absorbed in deionized water, resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.
Applications
Hydrochloric acid is a strong inorganic acid that is used in many industrial processes such as refining metal. The application often determines the required product quality. Hydrogen chloride, not hydrochloric acid, is used more widely in industrial organic chemistry, e.g. for vinyl chloride and dichloroethane.
Pickling of steel
One of the most important applications of hydrochloric acid is in the pickling of steel, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling, galvanizing, and other techniques. Technical quality HCl at typically 18% concentration is the most commonly used pickling agent for the pickling of carbon steel grades.
- {\displaystyle {\ce {Fe3O4 + Fe + 8 HCl -> 4 FeCl2 + 4 H2O}}}
The spent acid has long been reused as iron(II) chloride (also known as ferrous chloride) solutions, but high heavy-metal levels in the pickling liquor have decreased this practice.
The steel pickling industry has developed hydrochloric acid regeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula:
- {\displaystyle {\ce {4 FeCl2 + 4 H2O + O2 -> 8 HCl + 2 Fe2O3}}}
By recuperation of the spent acid, a closed acid loop is established. The iron(III) oxide by-product of the regeneration process is valuable, used in a variety of secondary industries.
Production of inorganic compounds
Akin to its use for pickling, hydrochloric acid is used to dissolve many metals, metal oxides and metal carbonates. The conversion are often depicted in simplified equations:
- Zn + 2 HCl → ZnCl2 + H2
- NiO + 2 HCl → NiCl2 + H2O
- CaCO3 + 2 HCl → CaCl2 + CO2 + H2O
These processes are used to produce metal chlorides for analysis or further production.
pH control and neutralization
Hydrochloric acid can be used to regulate the acidity (pH) of solutions.
- {\displaystyle {\ce {OH^- + HCl -> H2O + Cl^-}}}
In industry demanding purity (food, pharmaceutical, drinking water), high-quality hydrochloric acid is used to control the pH of process water streams. In less-demanding industry, technical quality hydrochloric acid suffices for neutralizing waste streams and swimming pool pH control.
Regeneration of ion exchangers
High-quality hydrochloric acid is used in the regeneration of ion exchange resins. Cation exchange is widely used to remove ions such as Na+ and Ca2+ from aqueous solutions, producing demineralized water. The acid is used to rinse the cations from the resins. Na+ is replaced with H+ and Ca2+ with 2 H+.
Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries.
Laboratory use
Of the six common strong mineral acids in chemistry, hydrochloric acid is the monoprotic acid least likely to undergo an interfering oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it contains the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure reagent, make hydrochloric acid an excellent acidifying reagent. It is also inexpensive.
Hydrochloric acid is the preferred acid in titration for determining the amount of bases. Strong acid titrants give more precise results due to a more distinct endpoint. Azeotropic, or “constant-boiling”, hydrochloric acid (roughly 20.2%) can be used as a primary standard in quantitative analysis, although its exact concentration depends on the atmospheric pressure when it is prepared.
Other
Hydrochloric acid is used for a large number of small-scale applications, such as leather processing, household cleaning, and building construction. Oil production may be stimulated by injecting hydrochloric acid into the rock formation of an oil well, dissolving a portion of the rock, and creating a large-pore structure. Oil well acidizing is a common process in the North Sea oil production industry.
Hydrochloric acid has been used for dissolving calcium carbonate, e.g. such things as de-scaling kettles and for cleaning mortar off brickwork. When used on brickwork the reaction with the mortar only continues until the acid has all been converted, producing calcium chloride, carbon dioxide, and water:
- {\displaystyle {\ce {CaCO3 + 2 HCl -> CaCl2 + CO2 + H2O}}}
Many chemical reactions involving hydrochloric acid are applied in the production of food, food ingredients, and food additives. Typical products include aspartame, fructose, citric acid, lysine, hydrolyzed vegetable protein as food enhancer, and in gelatin production. Food-grade (extra-pure) hydrochloric acid can be applied when needed for the final product.
Presence in living organisms
Gastric acid is one of the main secretions of the stomach. It consists mainly of hydrochloric acid and acidifies the stomach content to a pH of 1 to 2. Chloride (Cl−) and hydrogen (H+) ions are secreted separately in the stomach fundus region at the top of the stomach by parietal cells of the gastric mucosa into a secretory network called canaliculi before it enters the stomach lumen.
Gastric acid acts as a barrier against microorganisms to prevent infections and is important for the digestion of food. Its low pH denatures proteins and thereby makes them susceptible to degradation by digestive enzymes such as pepsin. The low pH also activates the enzyme precursor pepsinogen into the active enzyme pepsin by self-cleavage. After leaving the stomach, the hydrochloric acid of the chyme is neutralized in the duodenum by bicarbonate.
The stomach itself is protected from the strong acid by the secretion of a thick mucus layer, and by secretin induced buffering with sodium bicarbonate. Heartburn or peptic ulcers can develop when these mechanisms fail. Drugs of the antihistaminic and proton pump inhibitor classes can inhibit the production of acid in the stomach, and antacids are used to neutralize excessive existing acid.
Safety
Being a strong acid, hydrochloric acid is corrosive to living tissue and to many materials, but not to rubber. Typically, rubber protective gloves and related protective gear are used when handling concentrated solutions.
Mass fraction | Classification | List of H-phrases |
---|---|---|
10% ≤ C < 25% | Causes skin irritation, Causes serious eye irritation, | H315, H319 |
C ≥ 10% | May cause respiratory irritation | H335 |
C ≥ 25% | Causes severe skin burns and eye damage | H314 |
Legal status
Hydrochloric acid has been listed as a Table II precursor under the 1988 United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances because of its use in the production of heroin, cocaine, and methamphetamine.