The compound A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds hydrogen chloride has the formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound H Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its Cl Chlorine (pronounced /ˈklɔəriːn/ KLOR-een, from the Greek word 'χλωρóς' , is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to. At room temperature, it is a colorless gas Gas is one of three classical states of matter. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are so energized that they leave their parent atoms, which forms white fumes of hydrochloric acid Hydrochloric acid is the solution of hydrogen chloride (H upon contact with atmospheric humidity Humidity is the amount of water vapor in the air. Relative humidity is defined as the ratio of the partial pressure of water vapor in a parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature. Humidity may also be expressed as specific humidity. Relative humidity is an important metric used in forecasting weather. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. The formula HCl is often used to refer, somewhat misleadingly, to hydrochloric acid Hydrochloric acid is the solution of hydrogen chloride (H , an aqueous solution that can be derived from hydrogen chloride.

Chemistry

Hydrogen chloride is composed of diatomic Diatomic molecules are molecules composed only of two atoms, of either the same or different chemical elements. The prefix di- means two in Greek. Common diatomic molecules are hydrogen, nitrogen, oxygen, and carbon monoxide. Most elements aside from the noble gases form diatomic molecules when heated, but high temperatures—sometimes thousands molecules, each consisting of a hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its atom The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol is a simple HTTP-based protocol for creating and updating web resources H and a chlorine Chlorine (pronounced /ˈklɔəriːn/ KLOR-een, from the Greek word 'χλωρóς' , is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to atom Cl connected by a covalent A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, and other covalent bonds. In short, the attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding single bond Bond order is the number of chemical bonds between a pair of atoms. For example, in diatomic nitrogen N≡N the bond order is 3, while in acetylene H−C≡C−H the bond order between the two carbon atoms is also 3, and the C−H bond order is 1. Bond order gives an indication to the stability of a bond. In a more advanced context, bond order. Since the chlorine atom is much more electronegative Electronegativity, symbol χ , is a chemical property that describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) towards itself. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus. The higher the than the hydrogen atom, the covalent bond between the two atoms is quite polar. Consequently, the molecule has a large dipole moment with a negative partial charge A partial charge is a charge with an absolute value of less than one elementary charge unit δ⁻ at the chlorine atom and a positive partial charge δ⁺ at the hydrogen atom. In part due to its high polarity, HCl is very soluble Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure. The extent of the solubility of a substance in a in water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam (and in other polar solvents A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature. Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as a paint thinner (e.g. toluene, turpentine), as nail polish removers and).

Upon contact, H₂O and HCl combine to form hydronium In chemistry, hydronium is the common name for the aqueous cation H3O+, the type of oxonium ion, produced by protonation of water. It is the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton to the surrounding water molecules (H2O) cations An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. An anion , from the Greek word ἀνω (anο), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively H₃O⁺ and chloride The chloride ion is formed when the element chlorine picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides anions An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. An anion , from the Greek word ἀνω (anο), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively Cl⁻ through a reversible chemical reaction A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass:

HCl + H₂O → H₃O⁺ + Cl⁻

The resulting solution is called hydrochloric acid Hydrochloric acid is the solution of hydrogen chloride (H and is a strong acid More precisely, the acid must be stronger in aqueous solution than hydronium ion, so strong acids are acids with a pKa > −1.74 . This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution. While strong acids are. The acid dissociation An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The equilibrium can be written symbolically as: or ionization constant, K_a, is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with formula C , protonate Upon protonating a substrate, the mass and the charge of the species each increase by one unit. Protonating or deprotonating a molecule or ion alters many chemical properties beyond the change in the charge and mass: hydrophilicity, reduction potential, optical properties, among others. Protonation is also an essential step in certain analytical molecules or ions, and serve as an acid-catalyst Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive for chemical reactions where anhydrous (water-free) conditions are desired.

HCl + CH₃OH → CH₃O⁺H₂ + Cl⁻

Because of its acidic nature, hydrogen chloride is a corrosive A corrosive substance is one that will destroy or irreversibly damage another surface or substance with which it comes into contact. The main hazards to people include damage to the eyes, the skin, and the tissue under the skin; inhalation or ingestion of a corrosive substance can damage the respiratory and gastrointestinal tracts. Exposure gas, particularly in the presence of any moisture.

Structure and properties

The infrared spectrum Infrared spectroscopy is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum. It covers a range of techniques, the most common being a form of absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify compounds or investigate sample composition. Infrared spectroscopy of gaseous hydrogen chloride consists of a number of sharp absorption lines grouped around 2886 cm⁻¹ (wavelength ~3.47 µm). The HCl molecule absorbs photons, and converts it to kinetic energy in the form of rotation and vibration, that becomes heat In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body in collective behavior.

A chemical bond may be viewed simply as a spring with a certain Hooke's constant. However, due to quantum mechanical rules, only certain vibrational modes are permitted. The energy within this spring can be written thus:

E(v) = hν_e(v + 1/2)

At room temperature, almost all molecules in the ground state v = 0. To promote an HCl molecule to the v = 1 state, we would expect to see an infrared absorption about 2880 cm⁻¹. This absorption corresponding to the Q-branch is not observed due to it being forbidden due to symmetry. Instead, two sets of signals (P- and R-branches) are seen due to rotation of the molecules.

Due to quantum mechanical rules, only certain rotational modes are permitted. They are characterized by the rotational quantum number J = 0, 1, 2, 3, ... ΔJ can only take values of ± 1.

E(J) = h·B·J(J+1)

The value of B is much smaller than ν e, such that a much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region. However, due to the vibrational energy of this molecule, the set of absorptions lie within the infrared region, allowing a spectrum showing the rovibrational modes of this molecule to be easily collected using an ordinary infrared spectrometer with a conventional gas cell.

Plotting the assigned rotational quantum numbers (of fundamental transitions) of the R branch and P branch (J+1 and −J respectively) versus their energies (usually in cm⁻¹) and taking a third order regression of the data allows for the calculation of the centrifugal distortion constant, moment of inertia, average bond length, the coupling constant, and other useful information.

Naturally abundant chlorine consists of two isotopes, ³⁵Cl and ³⁷Cl, in a ratio of approximately 3:1. While the spring constants are very similar, the reduced masses Reduced mass is the "effective" inertial mass appearing in the two-body problem of Newtonian mechanics. This is a quantity with the unit of mass, which allows the two-body problem to be solved as if it were a one-body problem. Note however that the mass determining the gravitational force is not reduced. In the computation one mass can are different causing significant differences in the rotational energy, thus doublets are observed on close inspection of each absorption line, weighted in the same ratio of 3:1.

Production

Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid Hydrochloric acid is the solution of hydrogen chloride (H production.

Direct synthesis

In the chlor-alkali A Chloralkali process always implies the electrolysis of common salt or sodium chloride. Depending on the method several products beside hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide are the products; by mixing, sodium hypochlorite or sodium chlorate are produced, depending on the temperature. Higher industry, brine (mixture of sodium chloride and water) solution is electrolyzed In chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell producing chlorine Chlorine (pronounced /ˈklɔəriːn/ KLOR-een, from the Greek word 'χλωρóς' , is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to (Cl₂), sodium hydroxide Sodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around 45 million tonnes.[citation needed] Sodium hydroxide, and hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its (H₂). The pure chlorine gas can be combined with hydrogen to produce hydrogen chloride.

Cl₂ + H₂ → 2HCl

As the reaction is exothermic An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:, the installation is called an HCl oven An oven is an enclosed compartment for heating, baking or drying. It is most commonly used in cooking and pottery. Ovens used in pottery are also known as kilns. An oven used for heating or for industrial processes is called a furnace or industrial oven. In modern times the oven is used to cook and heat food in many households across the globe or HCl Burner. The resulting hydrogen chloride gas is absorbed Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, not by the surface . A more general term is "sorption", which in deionized water Purified water is water from any source that is physically processed to remove impurities. Distilled water and deionized water have been the most common forms of purified water, but water can also be purified by other processes including reverse osmosis, carbon filtration, microporous filtration, ultrafiltration, ultraviolet oxidation, or, resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.

Organic synthesis

The largest production of hydrochloric acid is integrated with the formation of chlorinated Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water which has been treated with chlorine is effective in preventing the spread of waterborne disease and fluorinated Fluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule. F2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the most chemically reactive and electronegative of all the elements. For organic Organic chemistry is a discipline within chemistry that involves the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as compounds, e.g., Teflon In chemistry, polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon, Freon A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass is the hydrochlorofluorocarbons (HCFCs), which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon. The most common representative is, and other CFCs, as well as chloroacetic acid, and PVC. Often this production of hydrochloric acid is integrated with captive use of it on-site. In the chemical reactions, hydrogen atoms on the hydrocarbon are replaced by chlorine atoms, where upon the released hydrogen atom recombines with the spare atom from the chlorine molecule, forming hydrogen chloride. Fluorination is a subsequent chlorine-replacement reaction, producing again hydrogen chloride.

R-H + Cl₂ → R-Cl + HCl

R-Cl + HF → R-F + HCl

The resulting hydrogen chloride gas is either reused directly, or absorbed in water, resulting in hydrochloric acid of technical or industrial grade.

Laboratory methods

Small amounts of HCl gas for laboratory use can be generated in a HCl generator by dehydrating hydrochloric acid with either sulfuric acid or anhydrous calcium chloride. Alternatively, HCl can be generated by the reaction of sulfuric acid with sodium chloride:^[1]

2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl↑

HCl can also be prepared by the hydrolysis of certain reactive chloride compounds such as phosphorus chlorides, thionyl chloride (SOCl₂), and acyl chlorides. Adding more water would absorb the HCl gas forming hydrochloric acid. For example, cold water can be gradually dripped onto phosphorus pentachloride (PCl₅) to give HCl in this reaction:

PCl₅ + H₂O → POCl₃ + 2HCl

Hot water could liberate more HCl by hydrolyzing PCl₅ all the way to ortho-phosphoric acid. Reaction of water with phosphorus trichloride (PCl₃) also yields HCl. Reaction of thionyl chloride with water would give sulfur dioxide (SO₂) gas as well as HCl. For the reactions of thionyl chloride or acyl chlorides with water, see thionyl chloride or acyl halide.

Applications

Most hydrogen chloride is used in the production of hydrochloric acid. It is also an important reagent in other industrial chemical transformations, e.g.:

• Hydrochlorination of rubber
• Production of vinyl and alkyl chlorides

In the semiconductor industry, it is used to both etch semiconductor crystals and to purify silicon via SiHCl₃.

It may also be used to treat cotton to delint it, and to separate it from wool.^{[citation needed]}

Where anhydrous hydrogen chloride is desired for small scale laboratory work, the gas is available in cylinders.

History

Alchemists of the Middle Ages recognized that hydrochloric acid (then known as spirit of salt or acidum salis) released vaporous hydrogen chloride, which was called marine acid air. In the 17th century, Johann Rudolf Glauber used salt (sodium chloride) and sulfuric acid for the preparation of sodium sulfate, releasing hydrogen chloride gas (see production, below). In 1772, Carl Wilhelm Scheele also reported this reaction and is sometimes credited with its discovery. Joseph Priestley prepared hydrogen chloride in 1772, and in 1810 Humphry Davy established that it is composed of hydrogen and chlorine.^[2]

During the Industrial Revolution, demand for alkaline substances such as soda ash increased, and Nicolas Leblanc developed a new industrial-scale process for producing the soda ash. In the Leblanc process, salt was converted to soda ash, using sulfuric acid, limestone, and coal, giving hydrogen chloride as by-product. Initially, this gas was vented to air, but the Alkali Act of 1863 prohibited such release, so then soda ash producers absorbed the HCl waste gas in water, producing hydrochloric acid on an industrial scale. Later, the Hargreaves process was developed, which is similar to the Leblanc process except sulfur dioxide, water, and air are used instead of sulfuric acid in a reaction which is exothermic overall. In the early 20th century the Leblanc process was effectively replaced by the Solvay process, which did not produce HCl. However, hydrogen chloride production continued as a step in hydrochloric acid production.

Historical uses of hydrogen chloride in the 20th century include hydrochlorinations of alkynes in producing the chlorinated monomers chloroprene and vinyl chloride, which are subsequently polymerized to make polychloroprene (Neoprene) and polyvinyl chloride (PVC), respectively. In the production of vinyl chloride, acetylene (C₂H₂) is hydrochlorinated by adding the HCl across the triple bond of the C₂H₂ molecule, turning the triple into a double bond, yielding vinyl chloride.

The "acetylene process", used until the 1960s for making chloroprene, starts out by joining two acetylene molecules, and then adds HCl to the joined intermediate across the triple bond to convert it to chloroprene as shown here:

This "acetylene process" has been replaced by a process which adds Cl₂ to one of the double bonds in 1,3-butadiene instead, and subsequent elimination produces HCl instead, as well as chloroprene.

Safety

Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause redness, pain, and severe skin burns. Hydrogen chloride may cause severe burns to the eye and permanent eye damage.

See also

• Chloride, inorganic salts of hydrochloric acid
• Hydrochloride, organic salts of hydrochloric acid

References

1. ^ Francisco J. Arnsliz (1995). "A Convenient Way To Generate Hydrogen Chloride in the Freshman Lab". J. Chem. Ed. 72: 1139. doi:10.1021/ed072p1139 (inactive 2010-01-09). http://jchemed.chem.wisc.edu/journal/Issues/1995/Dec/abs1139.html.
2. ^ Hartley, Harold (1960). "The Wilkins Lecture. Sir Humphry Davy, Bt., P.R.S. 1778-1829". Proceedings of the Royal Society of London (A) 255 (1281): 153 – 180. doi:10.1098/rspa.1960.0060. Bibcode: 1960RSPSA.255..153H.

2. Thames & Kosmos Chem C2000 Experiment Manual

External links

• International Chemical Safety Card 0163

Categories: Hydrogen compounds | Chlorides | Hazardous air pollutants | Nonmetal halides

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