Acid dissociation constant
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. K a =; the chemical species HA, A−, H+ are said to be in equilibrium when their concentrations do not change with the passing of time, because both forward and backward reactions are occurring at the same fast rate. The chemical equation for acid dissociation can be written symbolically as: HA ↽ − − ⇀ A − + H + where HA is a generic acid that dissociates into A−, the conjugate base of the acid and a hydrogen ion, H+, it is implicit in this definition that the quotient of activity coefficients, Γ, Γ = γ A − γ H + γ A H is a constant that can be ignored in a given set of experimental conditions. For many practical purposes it is more convenient to discuss the logarithmic constant, pKa p K a = − log 10 The more positive the value of pKa, the smaller the extent of dissociation at any given pH —that is, the weaker the acid.
A weak acid has a pKa value in the approximate range −2 to 12 in water. For a buffer solution consisting of a weak acid and its conjugate base, pKa can be expressed as: p K a = pH − log 10 The pKa for a weak monoprotic acid is conveniently determined by potentiometric titration with a strong base to the equivalence point and taking the pH value measured at one-half this volume as being equal to pKa; that is because at this half equivalence point, the number of moles of strong base added is one-half the number of moles of weak acid present, while the concentrations of the conjugate base and the remaining weak acid are the same. Acids with a pKa value of less than about −2 are said to be strong acids. In water, the dissociation of a strong acid in dilute solutions is complete such that the final concentration of the undissociated acid final is low. Consider a strong monoprotic acid, such as HCl; because of their 1:1 ratio, the final concentration of the conjugate base, final, is taken to be equal to the concentration of the hydronium ion, which can be directly measured by a pH meter.
For strong monoprotic acids like HCl, final and are both nearly equal to the initial concentration of initial placed into solution. With conventional acid-base titration methods it is difficult to measure the pH of a strong acid solution and, hence, to determine the or final, with a sufficient number of significant figures to and compute the low values encountered for final, which can be as low as 10-9 mol per liter for some strong acids. Furthermore, if 100% dissociation is assumed, final is zero and the fraction within parenthesis in the equation above becomes undefined; because the second expression on the right-hand side of the above equation is therefore indeterminable by conventional titration methods, the entire equation is not as useful a means of experimentally measuring pKa for strong acids as it is for weak acids. However, pKa and/or Ka values for strong acids can be estimated by theoretical means, such as computing gas phase dissociation constants and using Gibbs free energies of solvation for the molecular anions.
It is possible to use spectroscopy in some cases to determine the ratio of the concentrations of the conjugate base produced and the undissociated acid. For example, the Raman spectra of dilute nitric acid solutions contain signals of the nitrate ion and as the solutions become more concentrated signals of undissociated nitric acid molecules emerge; the acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction. The value of the pKa changes with temperature and can be understood qualitatively based on Le Châtelier's principle: when the reaction is endothermic, Ka increases and pKa decreases with
Succinic acid is a dicarboxylic acid with the chemical formula 22. The name derives from Latin succinum. In living organisms, succinic acid takes the form of an anion, which has multiple biological roles as a metabolic intermediate being converted into fumarate by the enzyme succinate dehydrogenase in complex 2 of the electron transport chain, involved in making ATP, as a signaling molecule reflecting the cellular metabolic state, it is marketed as food additive E363. Succinate is generated in mitochondria via the tricarboxylic acid cycle, an energy-yielding process shared by all organisms. Succinate can exit the mitochondrial matrix and function in the cytoplasm as well as the extracellular space, changing gene expression patterns, modulating epigenetic landscape or demonstrating hormone-like signaling; as such, succinate links cellular metabolism ATP formation, to the regulation of cellular function. Dysregulation of succinate synthesis, therefore ATP synthesis, happens in some genetic mitochondrial diseases, such as Leigh syndrome, Melas syndrome, degradation can lead to pathological conditions, such as malignant transformation and tissue injury.
Succinic acid is a white, odorless solid with a acidic taste. In an aqueous solution, succinic acid ionizes to form its conjugate base, succinate; as a diprotic acid, succinic acid undergoes two successive deprotonation reactions: 22 → 2− + H+ 2− → 222− + H+The pKa of these processes are 4.3 and 5.6, respectively. Both anions are colorless and can be isolated as the salts, e.g. Na2 and Na2222−. In living organisms succinate, not succinic acid, is found; as a radical group it is called a succinyl group. Like most simple mono- and dicarboxylic acids, it is not harmful but can be an irritant to skin and eyes. Succinic acid can be oxidized to fumaric acid or be converted to diesters, such as diethylsuccinate 2; this diethyl ester is a substrate in the Stobbe condensation. Dehydration of succinic acid gives succinic anhydride. Succinate can be used to derive 1,4-butanediol, maleic anhydride, succinimide, 2-pyrrolidinone and tetrahydrofuran. Succinic acid was obtained from amber by distillation and has thus been known as spirit of amber.
Today, succinic acid is generated for human use synthetically or converted from biomass via fermentation. Common industrial routes of synthesis include partial hydrogenation of maleic acid, oxidation of 1,4-butanediol, carbonylation of ethylene glycol. Succinate is produced petrochemically from butane via maleic anhydride. Additionally, genetic engineering of microorganisms, such as Escherichia coli or Saccharomyces cerevisiae, has allowed for the high-yielding, commercial production from fermentation of glucose. Global production is estimated at 16,000 to 30,000 tons a year, with an annual growth rate of 10%. In 2004, succinate was placed on the US Department of Energy's list of top 12 platform chemicals from biomass. Succinic acid is a component of some alkyd resins. 1,4-Butanediol can be synthesized using succinic as a precursor. The automotive and electronics industries rely on BDO to produce connectors, wheel covers, gearshift knobs and reinforcing beams. Succinic acid serves as the bases of certain biodegradable polymers, which are of interest in tissue engineering applications.
Acylation with succinic acid is called succination. Oversuccination occurs; as a food additive and dietary supplement, succinic acid is recognized as safe by the U. S. Food and Drug Administration. Succinic acid is used as an acidity regulator in the food and beverage industry, it is available as a flavoring agent, contributing a somewhat sour and astringent component to umami taste. As an excipient in pharmaceutical products, it is used to control acidity or as a counter ion. Drugs involving succinate include metoprolol succinate, sumatriptan succinate, Doxylamine succinate or solifenacin succinate. Succinate is a key intermediate in the tricarboxylic acid cycle, a primary metabolic pathway used to produce chemical energy in the presence of O2. Succinate is generated from succinyl-CoA by the enzyme succinyl-CoA synthetase in a GTP/ATP-producing step:Succinyl-CoA + NDP + Pi → Succinate + CoA + NTP Catalyzed by the enzyme succinate dehydrogenase, succinate is subsequently oxidized to fumarate:Succinate + FAD → Fumarate + FADH2SDH participates in the mitochondrial electron transport chain, where it is known as respiratory Complex 2.
This enzyme complex is a 4 subunit membrane-bound lipoprotein which couples the oxidation of succinate to the reduction of ubiquinone via the intermediate electron carriers FAD and three 2Fe-2S clusters. Succinate thus serves as a direct electron donor to the electron transport chain, itself is converted into fumarate. Click on genes and metabolites below to link to respective articles. Succinate can alternatively be formed by reverse activity of SDH. Under anaerobic conditions certain bacteria such as A. succinogenes, A. succiniciproducens and M. succiniciproducens, run the TCA cycle in reverse and convert glucose to succinate through the intermediates of oxaloacetate and fumarate. This pathway is exploited in metabolic engineering to net generate succinate for human use. Additionally, succinic acid produced during the fermentation of sugar provides a combination of saltiness and acidity to fermented alcohols. Accumulation of fumarate can drive the reverse activity of SDH. Under pathological and physiological conditions, the
Oxalate is the dianion with the formula C2O2−4 written 2−2. Either name is used for derivatives, such as salts of oxalic acid, for example sodium oxalate Na2C2O4, or dimethyl oxalate. Oxalate forms coordination compounds where it is sometimes abbreviated as ox. Many metal ions form insoluble precipitates with oxalate, a prominent example being calcium oxalate, the primary constituent of the most common kind of kidney stones; the dissociation of protons from oxalic acid proceeds in a stepwise manner as for other polyprotic acids. Loss of a single proton results in the monovalent hydrogenoxalate anion HC2O−4. A salt with this anion is sometimes called monobasic oxalate, or hydrogen oxalate; the equilibrium constant for loss of the first proton is 5.37×10−2. The loss of the second proton, which yields the oxalate ion, has an equilibrium constant of 5.25×10−5. These values imply, in solutions with neutral pH, no oxalic acid and only trace amounts of hydrogen oxalate exist; the literature is unclear on the distinction between H2C2O4, HC2O−4, C2O2−4, the collection of species is referred to as oxalic acid.
X-ray crystallography of simple oxalate salts show that the oxalate anion may adopt either a planar conformation with D2h molecular symmetry, or a conformation where the O–C–C–O dihedrals approach 90° with approximate D2d symmetry. The oxalate moiety adopts the planar, D2h conformation in the solid-state structures of M2C2O4. However, in structure of Cs2C2O4 the O–C–C–O dihedral angle is 81°. Therefore, Cs2C2O4 is more approximated by a D2d symmetry structure because the two CO2 planes are staggered. Two forms of Rb2C2O4 have been structurally characterized by single-crystal X-ray diffraction; as the preceding examples indicate that the conformation adopted by the oxalate dianion is dependent upon the size of the alkali metal to which it is bound, some have explored the barrier to rotation about the central C−C bond. The barrier to rotation about this bond was determined computationally to be 2–6 kcal/mol for the free dianion, C2O2−4; such results are consistent with the interpretation that the central carbon–carbon bond is best regarded as a single bond with only minimal pi interactions between the two CO−2 units.
This barrier to rotation about the C−C bond may be attributed to electrostatic interactions as unfavorable O−O repulsion is maximized in the planar form. Oxalate is encountered as a bidentate, chelating ligand, such as in potassium ferrioxalate; when the oxalate chelates to a single metal center, it always adopts the planar conformation. Oxalate occurs in many plants. Oxalate-rich plants include fat hen and several Oxalis species; the root and/or leaves of buckwheat are high in oxalic acid. Other edible plants that contain significant concentrations of oxalate include, in decreasing order, star fruit, black pepper, poppy seed, spinach, beets, chocolate, most nuts, most berries, fishtail palms, New Zealand spinach, beans. Leaves of the tea plant contain among the greatest measured concentrations of oxalic acid relative to other plants. However, the beverage derived by infusion in hot water contains only low to moderate amounts of oxalic acid due to the small mass of leaves used for brewing. In the body, oxalic acid combines with divalent metallic cations such as calcium and iron to form crystals of the corresponding oxalates which are excreted in urine as minute crystals.
These oxalates can form larger kidney stones. An estimated 80% of kidney stones are formed from calcium oxalate; those with kidney disorders, rheumatoid arthritis, or certain forms of chronic vulvar pain are advised to avoid foods high in oxalic acid. Methods to reduce the oxalate content in food are of current interest. Magnesium oxalate is 567 times more soluble than calcium oxalate, so the latter is more to precipitate out when magnesium levels are low and calcium and oxalate levels are high. Magnesium oxalate is a million times more soluble than mercury oxalate. Oxalate solubility for metals decreases in the order; the insoluble iron oxalate appears to play a major role in gout, in the nucleation and growth of the otherwise soluble sodium urate. This explains why gout appears after age 40, when ferritin levels in blood exceed 1 μg/L. Foods high in oxalate should be avoided by people suffering at risk of gout. Cadmium catalyzes the transformation of vitamin C into oxalic acid; this can be a problem for people exposed to high levels of cadmium in their diets, in the workplace, or through smoking.
In studies with rats, calcium supplements given along with foods high in oxalic acid can cause calcium oxalate to precipitate in the gut and reduce the levels of oxalate absorbed by the body Oxalic acid can be produced by the metabolism of ethylene glycol, glyoxylic acid, or ascorbic acid. Powdered oxalate is used as a pesticide in beekeeping to combat the bee mite; some fungi of the genus Aspergillus produce oxalic acid. Some preliminary evidence indicates the administration of probiotics can affect oxalic acid excretion rates in a positive manner. Oxalate, the conjugate base of oxalic acid, is an excellent ligand for metal ions
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water at 93.4 °C at 1,905 metres altitude. For a given pressure, different liquids will boil at different temperatures; the normal boiling point of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid; the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar.
The heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the liquid's edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid. A saturated liquid contains as much thermal energy. Saturation temperature means boiling point; the saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed.
A liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, or the IUPAC standard pressure of 100.000 kPa. At higher elevations, where the atmospheric pressure is much lower, the boiling point is lower; the boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point; the boiling point decreases with decreasing pressure until the triple point is reached. The boiling point cannot be reduced below the triple point. If the heat of vaporization and the vapor pressure of a liquid at a certain temperature are known, the boiling point can be calculated by using the Clausius–Clapeyron equation, thus: T B = − 1, where: T B is the boiling point at the pressure of interest, R is the ideal gas constant, P is the vapour pressure of the liquid at the pressure of interest, P 0 is some pressure where the corresponding T 0 is known, Δ H vap is the heat of vaporization of the liquid, T 0 is the boiling temperature, ln is the natural logarithm.
Saturation pressure is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased, so is saturation temperature. If the temperature in a system remains constant, vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. A liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased. There are two conventions regarding the standard boiling point of water: The normal boiling point is 99.97 °C at a pressure of 1 atm. The IUPAC recommended standard boiling point of water at a standard pressure of 100 kPa is 99.61 °C. For comparison, on top of Mount Everest, at 8,848 m elevation, the pressure is about 34 kPa and the boiling point of water is 71 °C; the Celsius temperature scale was defined until 1954 by two points: 0 °C being defined by the wate
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t
The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are equal. For example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures.
For example, agar melts at 85 °C and solidifies from 31 °C. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances, the freezing point of water is not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its enthalpy of fusion.
A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees.
The spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source, calibrated as a function of temperature. In this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer. For temperatures above the calibration range of the source, an extrapolation technique must be employed; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website