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95-417: The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide . At room temperature , it is a colorless gas , which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor . Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given

190-424: A chemical compound ; the concept is most readily understood when considering pure chemical substances . It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction , into compounds or substances each having fewer atoms. A chemical formula is a way of expressing information about the proportions of atoms that constitute

285-402: A monochromator . Alternatively, the entire wavelength range is measured using a Fourier transform instrument and then a transmittance or absorbance spectrum is extracted. This technique is commonly used for analyzing samples with covalent bonds . The number of bands roughly correlates with symmetry and molecular complexity. A variety of devices are used to hold the sample in the path of

380-419: A solid-state reaction , or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points , and are hard and brittle . As solids they are almost always electrically insulating , but when melted or dissolved they become highly conductive , because the ions are mobilized. An intermetallic compound

475-401: A "two-beam" setup (see figure), can correct for these types of effects to give very accurate results. The Standard addition method can be used to statistically cancel these errors. Nevertheless, among different absorption-based techniques which are used for gaseous species detection, Cavity ring-down spectroscopy (CRDS) can be used as a calibration-free method. The fact that CRDS is based on

570-472: 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 : Hydrogen chloride can protonate molecules or ions and can also serve as an acid- catalyst for chemical reactions where anhydrous (water-free) conditions are desired. Because of its acidic nature, hydrogen chloride

665-426: A bond between atoms is stretched, for instance, there comes a point at which the bond breaks and the molecule dissociates into atoms. Thus real molecules deviate from perfect harmonic motion and their molecular vibrational motion is anharmonic . An empirical expression that fits the energy curve of a diatomic molecule undergoing anharmonic extension and compression to a good approximation was derived by P.M. Morse , and

760-408: A ceiling of 5 ppm (7 mg/m), and compiled extensive information on hydrogen chloride workplace safety concerns. Chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities ) containing atoms from more than one chemical element held together by chemical bonds . A molecule consisting of atoms of only one element

855-412: A continuous three-dimensional network, usually in a crystalline structure . Ionic compounds containing basic ions hydroxide (OH ) or oxide (O ) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions . Ionic compounds can also be produced from their constituent ions by evaporation of their solvent , precipitation , freezing ,

950-747: A convenient stand-off method to sort plastic of different polymers ( PET , HDPE , ...). Other developments include a miniature IR-spectrometer that's linked to a cloud based database and suitable for personal everyday use, and NIR-spectroscopic chips that can be embedded in smartphones and various gadgets. In catalysis research it is a very useful tool to characterize the catalyst, as well as to detect intermediates Infrared spectroscopy coupled with machine learning and artificial intelligence also has potential for rapid, accurate and non-invasive sensing of bacteria. The complex chemical composition of bacteria, including nucleic acids, proteins, carbohydrates and fatty acids, results in high-dimensional datasets where

1045-492: A different chemical composition by interaction with a second chemical compound via a chemical reaction . In this process, bonds between atoms are broken in both of the interacting compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AD + CB , where A, B, C, and D are each unique atoms; and AB, AD, CD, and CB are each unique compounds. Infrared spectrometer The infrared portion of

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1140-516: A disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the standard chemical symbols with numerical subscripts . Many chemical compounds have a unique CAS number identifier assigned by the Chemical Abstracts Service . Globally, more than 350,000 chemical compounds (including mixtures of chemicals) have been registered for production and use. The term "compound"—with

1235-452: A function of infrared wavelength (or equivalently, wavenumber ). As described above, the sample's spectrum is always compared to a reference. An alternate method for acquiring spectra is the "dispersive" or "scanning monochromator " method. In this approach, the sample is irradiated sequentially with various single wavelengths. The dispersive method is more common in UV-Vis spectroscopy , but

1330-444: A meaning similar to the modern—has been used at least since 1661 when Robert Boyle's The Sceptical Chymist was published. In this book, Boyle variously used the terms "compound", "compounded body", "perfectly mixt body", and "concrete". "Perfectly mixt bodies" included for example gold, lead, mercury, and wine. While the distinction between compound and mixture is not so clear, the distinction between element and compound

1425-418: A much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region. However, the vibrational energy of HCl molecule places its absorptions within the infrared region, allowing a spectrum showing the rovibrational transitions of this molecule to be easily collected using an infrared spectrometer with a gas cell. The latter can even be made of quartz as

1520-403: A number of other salts such as potassium bromide or calcium fluoride are also used). The plates are transparent to the infrared light and do not introduce any lines onto the spectra. With increasing technology in computer filtering and manipulation of the results, samples in solution can now be measured accurately (water produces a broad absorbance across the range of interest, and thus renders

1615-566: A particular chemical compound, using chemical symbols for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H 2 O. In the case of non-stoichiometric compounds , the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride , PdH x (0.02 < x < 0.58)]. Chemical compounds have

1710-496: A positively charged cation . The nonmetal will gain the electrons from the metal, making the nonmetal a negatively charged anion . As outlined, ionic bonds occur between an electron donor, usually a metal, and an electron acceptor, which tends to be a nonmetal. Hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom forms an electrostatic connection with another electronegative atom through interacting dipoles or charges. A compound can be converted to

1805-794: A sample to be "IR active", it must be associated with changes in the molecular dipole moment. A permanent dipole is not necessary, as the rule requires only a change in dipole moment. A molecule can vibrate in many ways, and each way is called a vibrational mode . For molecules with N number of atoms, geometrically linear molecules have 3 N  – 5 degrees of vibrational modes, whereas nonlinear molecules have 3 N  – 6 degrees of vibrational modes (also called vibrational degrees of freedom). As examples linear carbon dioxide (CO 2 ) has 3 × 3 – 5 = 4, while non-linear water (H 2 O) , has only 3 × 3 – 6 = 3. Simple diatomic molecules have only one bond and only one vibrational band. If

1900-421: A simultaneous change in the rotational state of the molecules. Because of quantum mechanical selection rules, only certain rotational transitions are permitted. The states are characterized by the rotational quantum number J  = 0, 1, 2, 3, ... selection rules state that Δ J is only able to take values of ±1. The value of the rotational constant B is much smaller than the vibrational one ν o , such that

1995-447: A solid state dependent on how low the temperature of the environment is. A covalent bond , also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements , yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on

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2090-622: A technique for performing vibrational spectroscopy in a transmission electron microscope (TEM). In combination with the high spatial resolution of the TEM, unprecedented experiments have been performed, such as nano-scale temperature measurements, mapping of isotopically labeled molecules, mapping of phonon modes in position- and momentum-space, vibrational surface and bulk mode mapping on nanocubes, and investigations of polariton modes in van der Waals crystals. Analysis of vibrational modes that are IR-inactive but appear in inelastic neutron scattering

2185-469: A unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds . Chemical compounds can be molecular compounds held together by covalent bonds , salts held together by ionic bonds , intermetallic compounds held together by metallic bonds , or the subset of chemical complexes that are held together by coordinate covalent bonds . Pure chemical elements are generally not considered chemical compounds, failing

2280-502: Is a corrosive substance , particularly in the presence of moisture. Frozen HCl undergoes a phase transition at 98.4 K (−174.8 °C; −282.5 °F). X-ray powder diffraction of the frozen material shows that the material changes from an orthorhombic structure to a cubic one during this transition. In both structures the chlorine atoms are in a face-centered array . However, the hydrogen atoms could not be located. Analysis of spectroscopic and dielectric data, and determination of

2375-445: Is a central theme. Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury. Boyle used the concept of "corpuscles"—or "atomes", as he also called them—to explain how a limited number of elements could combine into a vast number of compounds: If we assigne to

2470-403: Is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as stoichiometric or nonstoichiometric intermetallic compounds. A coordination complex consists of a central atom or ion, which is usually metallic and is called

2565-570: Is also possible at high spatial resolution using EELS. Although the spatial resolution of HREELs is very high, the bands are extremely broad compared to other techniques. By using computer simulations and normal mode analysis it is possible to calculate theoretical frequencies of molecules. IR spectroscopy is often used to identify structures because functional groups give rise to characteristic bands both in terms of intensity and position (frequency). The positions of these bands are summarized in correlation tables as shown below. A spectrograph

2660-463: Is also used in forensic analysis in both criminal and civil cases, for example in identifying polymer degradation . It can be used in determining the blood alcohol content of a suspected drunk driver. IR spectroscopy has been used in identification of pigments in paintings and other art objects such as illuminated manuscripts . Infrared spectroscopy is also useful in measuring the degree of polymerization in polymer manufacture. Changes in

2755-511: Is called the Morse function . Using the Schrödinger equation leads to the selection rule for the system undergoing vibrational changes : △ v = ± 1 , ± 2 , ± 3 , ⋅ ⋅ ⋅ {\displaystyle \bigtriangleup v=\pm 1,\pm 2,\pm 3,\cdot \cdot \cdot } In order for a vibrational mode in

2850-528: Is composed of hydrogen and chlorine . 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

2945-624: Is consumed in the production of hydrochloric acid. It is also used in the production of vinyl chloride and many alkyl chlorides . Trichlorosilane , a precursor to ultrapure silicon, is produced by the reaction of hydrogen chloride and silicon at around 300 °C. Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi (c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac ( ammonium chloride ), which when it

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3040-456: Is guided through an interferometer and then through the sample (or vice versa). A moving mirror inside the apparatus alters the distribution of infrared light that passes through the interferometer. The signal directly recorded, called an "interferogram", represents light output as a function of mirror position. A data-processing technique called Fourier transform turns this raw data into the desired result (the sample's spectrum): light output as

3135-423: Is important for many clinical settings where faster susceptibility testing would decrease unnecessary blind-treatment with broad-spectrum antibiotics. The main limitation of this technique for clinical applications is the high sensitivity to technical equipment and sample preparation techniques, which makes it difficult to construct large-scale databases. Attempts in this direction have however been made by Bruker with

3230-465: Is in the food industry to measure the concentration of various compounds in different food products. Infrared spectroscopy is also used in gas leak detection devices such as the DP-IR and EyeCGAs. These devices detect hydrocarbon gas leaks in the transportation of natural gas and crude oil. Infrared spectroscopy is an important analysis method in the recycling process of household waste plastics , and

3325-855: Is less practical in the infrared than the FTIR method. One reason that FTIR is favored is called " Fellgett's advantage " or the "multiplex advantage": The information at all frequencies is collected simultaneously, improving both speed and signal-to-noise ratio . Another is called "Jacquinot's Throughput Advantage": A dispersive measurement requires detecting much lower light levels than an FTIR measurement. There are other advantages, as well as some disadvantages, but virtually all modern infrared spectrometers are FTIR instruments. Various forms of infrared microscopy exist. These include IR versions of sub-diffraction microscopy such as IR NSOM , photothermal microspectroscopy , Nano-FTIR and atomic force microscope based infrared spectroscopy (AFM-IR). Infrared spectroscopy

3420-424: Is more useful. For example, if the sample is a dilute solute dissolved in water in a beaker, then a good reference measurement might be to measure pure water in the same beaker. Then the reference measurement would cancel out not only all the instrumental properties (like what light source is used), but also the light-absorbing and light-reflecting properties of the water and beaker, and the final result would just show

3515-493: Is neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions . These can be simple ions such as the sodium (Na ) and chloride (Cl ) in sodium chloride , or polyatomic species such as the ammonium ( NH 4 ) and carbonate ( CO 3 ) ions in ammonium carbonate . Individual ions within an ionic compound usually have multiple nearest neighbours, so are not considered to be part of molecules, but instead part of

3610-458: Is not the only method of studying molecular vibrational spectra. Raman spectroscopy involves an inelastic scattering process in which only part of the energy of an incident photon is absorbed by the molecule, and the remaining part is scattered and detected. The energy difference corresponds to absorbed vibrational energy. The selection rules for infrared and for Raman spectroscopy are different at least for some molecular symmetries , so that

3705-452: Is often interpreted as having two regions. In the functional region there are one to a few troughs per functional group. In the fingerprint region there are many troughs which form an intricate pattern which can be used like a fingerprint to determine the compound. For many kinds of samples, the assignments are known, i.e. which bond deformation(s) are associated with which frequency. In such cases further information can be gleaned about

3800-414: Is then pressed in a mechanical press to form a translucent pellet through which the beam of the spectrometer can pass. A third technique is the "cast film" technique, which is used mainly for polymeric materials. The sample is first dissolved in a suitable, non- hygroscopic solvent. A drop of this solution is deposited on the surface of a KBr or NaCl cell. The solution is then evaporated to dryness and

3895-639: Is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction , which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds ; ionic compounds are held together by ionic bonds ; intermetallic compounds are held together by metallic bonds ; coordination complexes are held together by coordinate covalent bonds . Non-stoichiometric compounds form

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3990-615: 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

4085-449: The CH 2 portion: two stretching modes (ν): symmetric (ν s ) and antisymmetric (ν as ); and four bending modes: scissoring (δ), rocking (ρ), wagging (ω) and twisting (τ), as shown below. Structures that do not have the two additional X groups attached have fewer modes because some modes are defined by specific relationships to those other attached groups. For example, in water,

4180-452: The coordination centre , and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those of transition metals , are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex of d block element. Compounds are held together through a variety of different types of bonding and forces. The differences in

4275-415: The electromagnetic spectrum is usually divided into three regions; the near- , mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14,000–4,000 cm (0.7–2.5 μm wavelength) can excite overtone or combination modes of molecular vibrations . The mid-infrared, approximately 4,000–400 cm (2.5–25 μm) is generally used to study

4370-449: The oxygen molecule (O 2 ); or it may be heteronuclear , a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H 2 O). A molecule is the smallest unit of a substance that still carries all the physical and chemical properties of that substance. An ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding . The compound

4465-434: The triple bond to convert it to chloroprene as shown here: This "acetylene process" has been replaced by a process which adds Cl 2 to the double bond of ethylene instead, and subsequent elimination produces HCl instead, as well as chloroprene. Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing , choking , inflammation of

4560-896: The Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos’d of them. In his Logick , published in 1724, the English minister and logician Isaac Watts gave an early definition of chemical element, and contrasted element with chemical compound in clear, modern terms. Among Substances, some are called Simple, some are Compound ... Simple Substances ... are usually called Elements, of which all other Bodies are compounded: Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be

4655-459: The Earth. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. A molecule may be homonuclear , that is, it consists of atoms of one chemical element, as with two atoms in

4750-404: The HCl absorption lies in a window of transparency for this material. Naturally abundant chlorine consists of two isotopes, Cl and Cl, in a ratio of approximately 3:1. While the spring constants are nearly identical, the disparate reduced masses of HCl and HCl cause measurable differences in the rotational energy, thus doublets are observed on close inspection of each absorption line, weighted in

4845-460: The IR Biotyper for food microbiology. Infrared spectroscopy exploits the fact that molecules absorb frequencies that are characteristic of their structure . These absorptions occur at resonant frequencies , i.e. the frequency of the absorbed radiation matches the vibrational frequency. The energies are affected by the shape of the molecular potential energy surfaces , the masses of the atoms, and

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4940-487: The IR beam These devices are selected on the basis of their transparency in the region of interest and their resilience toward the sample. Gaseous samples require a sample cell with a long pathlength to compensate for the diluteness. The pathlength of the sample cell depends on the concentration of the compound of interest. A simple glass tube with length of 5 to 10 cm equipped with infrared-transparent windows at both ends of

5035-524: The Truth ;; tho' they are not all agreed ... Compound Substances are made up of two or more simple Substances ... So a Needle is simple Body, being made only of Steel; but a Sword or a Knife is a compound because its ... Handle is made of Materials different from the Blade. Any substance consisting of two or more different types of atoms ( chemical elements ) in a fixed stoichiometric proportion can be termed

5130-503: The absorption of a photon leading to a direct transition from the ground state to the second excited vibrational state ( v = 2). Such a band appears at approximately twice the energy of the fundamental band for the same normal mode. Some excitations, so-called combination modes , involve simultaneous excitation of more than one normal mode. The phenomenon of Fermi resonance can arise when two modes are similar in energy; Fermi resonance results in an unexpected shift in energy and intensity of

5225-547: The associated vibronic coupling . In particular, in the Born–Oppenheimer and harmonic approximations (i.e. when the molecular Hamiltonian corresponding to the electronic ground state can be approximated by a harmonic oscillator in the neighbourhood of the equilibrium molecular geometry ), the resonant frequencies are associated with the normal modes of vibration corresponding to the molecular electronic ground state potential energy surface. Thus, it depends on both

5320-416: The bands etc. The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. When the frequency of the IR matches the vibrational frequency of a bond or collection of bonds, absorption occurs. Examination of the transmitted light reveals how much energy was absorbed at each frequency (or wavelength). This measurement can be achieved by scanning the wavelength range using

5415-600: The character or quantity of a particular bond are assessed by measuring at a specific frequency over time. Instruments can routinely record many spectra per second in situ, providing insights into reaction mechanism (e.g., detection of intermediates) and reaction progress. Infrared spectroscopy is utilized in the field of semiconductor microelectronics: for example, infrared spectroscopy can be applied to semiconductors like silicon , gallium arsenide , gallium nitride , zinc selenide , amorphous silicon, silicon nitride , etc. Another important application of infrared spectroscopy

5510-403: The chemical composition included hydrogen and chlorine . Hydrogen chloride is produced by combining chlorine and hydrogen : 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

5605-454: The essential features are effectively hidden under the total spectrum. Extraction of the essential features therefore requires advanced statistical methods such as machine learning and deep-neural networks. The potential of this technique for bacteria classification have been demonstrated for differentiation at the genus, species and serotype taxonomic levels, and it has also been shown promising for antimicrobial susceptibility testing, which

5700-407: The film formed on the cell is analysed directly. Care is important to ensure that the film is not too thick otherwise light cannot pass through. This technique is suitable for qualitative analysis. The final method is to use microtomy to cut a thin (20–100 μm) film from a solid sample. This is one of the most important ways of analysing failed plastic products for example because the integrity of

5795-400: The fixed ratios. Many solid chemical substances—for example many silicate minerals —are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios; even so, these crystalline substances are often called " non-stoichiometric compounds ". It may be argued that they are related to, rather than being chemical compounds, insofar as

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5890-437: The food industry. The reaction can also be triggered by blue light. The industrial production of hydrogen chloride is often integrated with the formation of chlorinated and fluorinated organic compounds, e.g., Teflon , Freon , 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

5985-415: The formula HCl. Hydrogen chloride is a diatomic molecule , consisting of a hydrogen atom H and a chlorine atom Cl connected by a polar covalent bond . The chlorine atom is much more electronegative than the hydrogen atom, which makes this bond polar. Consequently, the molecule has a large dipole moment with a negative partial charge (δ−) at the chlorine atom and a positive partial charge (δ+) at

6080-508: The four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five : This seems to come nearer

6175-477: The fundamental vibrations and associated rotational–vibrational structure. The far-infrared, approximately 400–10 cm (25–1,000 μm) has low energy and may be used for rotational spectroscopy and low frequency vibrations. The region from 2–130 cm , bordering the microwave region, is considered the terahertz region and may probe intermolecular vibrations. The names and classifications of these subregions are conventions, and are only loosely based on

6270-642: The hydrocarbon are replaced by chlorine atoms, whereupon 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: The resulting hydrogen chloride is either reused directly or absorbed in water, resulting in hydrochloric acid of technical or industrial grade. Small amounts of hydrogen chloride for laboratory use can be generated in an HCl generator by dehydrating hydrochloric acid with either sulfuric acid or anhydrous calcium chloride . Alternatively, HCl can be generated by

6365-417: The hydrogen atom. In part because of its high polarity, HCl is very soluble in water (and in other polar solvents ). Upon contact, H 2 O and HCl combine to form hydronium cations [H 3 O] and chloride anions Cl through a reversible chemical reaction : The resulting solution is called hydrochloric acid and is a strong acid . The acid dissociation or ionization constant, K

6460-418: The measurements of photon life-times (and not the laser intensity) makes it needless for any calibration and comparison with a reference Some instruments also automatically identify the substance being measured from a store of thousands of reference spectra held in storage. Fourier transform infrared (FTIR) spectroscopy is a measurement technique that allows one to record infrared spectra. Infrared light

6555-607: The molecule is symmetrical, e.g. N 2 , the band is not observed in the IR spectrum, but only in the Raman spectrum . Asymmetrical diatomic molecules, e.g. carbon monoxide ( CO ), absorb in the IR spectrum. More complex molecules have many bonds, and their vibrational spectra are correspondingly more complex, i.e. big molecules have many peaks in their IR spectra. The atoms in a CH 2 X 2 group, commonly found in organic compounds and where X can represent any other atom, can vibrate in nine different ways. Six of these vibrations involve only

6650-432: The molecule, are much smaller than the movements of the lighter H atoms. The simplest and most important or fundamental IR bands arise from the excitations of normal modes, the simplest distortions of the molecule, from the ground state with vibrational quantum number v = 0 to the first excited state with vibrational quantum number v = 1. In some cases, overtone bands are observed. An overtone band arises from

6745-525: The nature of the bonds and the mass of the atoms that are involved. Using the Schrödinger equation leads to the selection rule for the vibrational quantum number in the system undergoing vibrational changes: △ v = ± 1 {\displaystyle \bigtriangleup v=\pm 1} The compression and extension of a bond may be likened to the behaviour of a spring , but real molecules are hardly perfectly elastic in nature. If

6840-530: 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 chemical burns . Hydrogen chloride may cause severe burns to the eye and permanent eye damage. The U.S. Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have established occupational exposure limits for hydrogen chloride at

6935-536: The periodic table tend to have similar electronegativities , which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet . Ionic bonding occurs when valence electrons are completely transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions. The metals in ionic bonding usually lose their valence electrons, becoming

7030-402: The production of vinyl chloride, acetylene ( C 2 H 2 ) is hydrochlorinated by adding the HCl across the triple bond of the C 2 H 2 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

7125-438: The properties of the solute (at least approximately). A common way to compare to a reference is sequentially: first measure the reference, then replace the reference by the sample and measure the sample. This technique is not perfectly reliable; if the infrared lamp is a bit brighter during the reference measurement, then a bit dimmer during the sample measurement, the measurement will be distorted. More elaborate methods, such as

7220-599: The reaction of sulfuric acid with sodium chloride: This reaction occurs at room temperature. Provided there is NaCl remaining in the generator and it is heated above 200 °C, the reaction proceeds further: For such generators to function, the reagents should be dry. Hydrogen chloride can also be prepared by the hydrolysis of certain reactive chloride compounds such as phosphorus chlorides , thionyl chloride ( SOCl 2 ), and acyl chlorides . For example, cold water can be gradually dripped onto phosphorus pentachloride ( PCl 5 ) to give HCl: Most hydrogen chloride

7315-410: The relative molecular or electromagnetic properties. Infrared spectroscopy is a simple and reliable technique widely used in both organic and inorganic chemistry, in research and industry. It is used in quality control, dynamic measurement, and monitoring applications such as the long-term unattended measurement of CO 2 concentrations in greenhouses and growth chambers by infrared gas analyzers. It

7410-411: The rocking, wagging, and twisting modes do not exist because these types of motions of the H atoms represent simple rotation of the whole molecule rather than vibrations within it. In case of more complex molecules, out-of-plane (γ) vibrational modes can be also present. These figures do not represent the " recoil " of the C atoms, which, though necessarily present to balance the overall movements of

7505-544: The same ratio of 3:1. Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production. In the 17th century, Johann Rudolf Glauber from Karlstadt am Main, Germany used sodium chloride salt and sulfuric acid for the preparation of sodium sulfate in the Mannheim process , releasing hydrogen chloride. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, and by 1808 Humphry Davy of Penzance, England had proved that

7600-417: The sample and a "reference". This step controls for a number of variables, e.g. infrared detector , which may affect the spectrum. The reference measurement makes it possible to eliminate the instrument influence. The appropriate "reference" depends on the measurement and its goal. The simplest reference measurement is to simply remove the sample (replacing it by air). However, sometimes a different reference

7695-404: The solid is preserved. In photoacoustic spectroscopy the need for sample treatment is minimal. The sample, liquid or solid, is placed into the sample cup which is inserted into the photoacoustic cell which is then sealed for the measurement. The sample may be one solid piece, powder or basically in any form for the measurement. For example, a piece of rock can be inserted into the sample cup and

7790-473: The spectra unreadable without this computer treatment). Solid samples can be prepared in a variety of ways. One common method is to crush the sample with an oily mulling agent (usually mineral oil Nujol ). A thin film of the mull is applied onto salt plates and measured. The second method is to grind a quantity of the sample with a specially purified salt (usually potassium bromide ) finely (to remove scattering effects from large crystals). This powder mixture

7885-419: The spectrum measured from it. A useful way of analyzing solid samples without the need for cutting samples uses ATR or attenuated total reflectance spectroscopy. Using this approach, samples are pressed against the face of a single crystal. The infrared radiation passes through the crystal and only interacts with the sample at the interface between the two materials. It is typical to record spectrum of both

7980-429: The structure of DCl (deuterium chloride) indicates that HCl forms zigzag chains in the solid, as does HF (see figure on right). The infrared spectrum of gaseous hydrogen chloride, shown on the left, consists of a number of sharp absorption lines grouped around 2886 cm (wavelength ~3.47 μm). At room temperature, almost all molecules are in the ground vibrational state v  = 0. Including anharmonicity

8075-438: The tube can be used for concentrations down to several hundred ppm. Sample gas concentrations well below ppm can be measured with a White's cell in which the infrared light is guided with mirrors to travel through the gas. White's cells are available with optical pathlength starting from 0.5 m up to hundred meters. Liquid samples can be sandwiched between two plates of a salt (commonly sodium chloride , or common salt, although

8170-406: The two methods are complementary in that they observe vibrations of different symmetries. Another method is electron energy loss spectroscopy (EELS), in which the energy absorbed is provided by an inelastically scattered electron rather than a photon. This method is useful for studying vibrations of molecules adsorbed on a solid surface. Recently, high-resolution EELS (HREELS) has emerged as

8265-494: The two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H 2 , or the polyatomic molecule S 8 , etc.). Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number . There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require

8360-455: The types of bonds in compounds differ based on the types of elements present in the compound. London dispersion forces are the weakest force of all intermolecular forces . They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole . Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, and to further freeze to

8455-421: The variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound , or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of

8550-490: The vibrational energy can be written as: To promote an HCl molecule from the v  = 0 to the v  = 1 state, we would expect to see an infrared absorption about ν o  =  ν e  + 2 x e ν e = 2880 cm. However, this absorption corresponding to the Q-branch is not observed due to it being forbidden by symmetry. Instead, two sets of signals (P- and R-branches) are seen owing to

8645-430: 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, above). 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

8740-571: Was discovered that it can be put to chemical use. One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts"), an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin by Gerard of Cremona (1144–1187). Another important development

8835-413: Was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride. It is possible that in one of his experiments, al-Razi stumbled upon a primitive method to produce hydrochloric acid . However, it appears that in most of these early experiments with chloride salts , the gaseous products were discarded, and hydrogen chloride may have been produced many times before it

8930-513: 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

9025-555: Was the discovery by pseudo-Geber (in the De inventione veritatis , "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid , a strong solvent capable of dissolving gold (i.e., aqua regia ) could be produced. After the discovery in the late sixteenth century of the process by which unmixed hydrochloric acid can be prepared, it was recognized that this new acid (then known as spirit of salt or acidum salis ) released vaporous hydrogen chloride, which

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