A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed by the reception of a proton by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid; because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic. In summary, this can be represented as the following chemical reaction: Acid + Base ⇌ Conjugate Base + Conjugate Acid Johannes Nicolaus Brønsted and Martin Lowry introduced the Brønsted–Lowry theory, which proposed that any compound that can transfer a proton to any other compound is an acid, the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge. A cation can be a conjugate acid, an anion can be a conjugate base, depending on which substance is involved and which acid–base theory is the viewpoint.
The simplest anion which can be a conjugate base is the solvated electron whose conjugate acid is the atomic hydrogen. In an acid-base reaction, an acid plus a base reacts to form a conjugate base plus a conjugate acid: Conjugates are formed when an acid loses a hydrogen proton or a base gains a hydrogen proton. Refer to the following figure: We say that the water molecule is the conjugate acid of the hydroxide ion after the latter received the hydrogen proton donated by ammonium. On the other hand, ammonia is the conjugate base for the acid ammonium after ammonium has donated a hydrogen ion towards the production of the water molecule. We can refer to OH- as a conjugate base of H2O, since the water molecule donates a proton towards the production of NH+4 in the reverse reaction, the predominating process in nature due to the strength of the base NH3 over the hydroxide ion. Based on this information, it is clear that the terms "Acid", "Base", "conjugate acid", "conjugate base" are not fixed for a certain chemical species.
The strength of a conjugate acid is directly proportional to its dissociation constant. If a conjugate acid is strong, its dissociation will have a higher equilibrium constant and the products of the reaction will be favored; the strength of a conjugate base can be seen as the tendency of the species to "pull" hydrogen protons towards itself. If a conjugate base is classified as strong, it will "hold on" to the hydrogen proton when in solution and its acid will not dissociate. On the other hand, if a species is classified as a strong acid, its conjugate base will be weak in nature. An example of this case would be the dissociation of Hydrochloric acid HCl in water. Since HCl is a strong acid, its conjugate base will be a weak conjugate base. Therefore, in this system, most H+ will be in the form of a Hydronium ion H3O+ instead of attached to a Cl anion and the conjugate base will be weaker than a water molecule. If an acid is weak, its conjugate base will be strong; when considering the fact that the Kw is equal to the product of the concentrations of H+ and OH.
A weak acid will have a low concentration of H+. The Kw divided by a low H+ concentration will result in a low OH- concentration as well. Therefore, weak acids will have weak conjugate bases, unlike the misconception that they have strong conjugate bases; the acid and conjugate base as well as the base and conjugate acid are known as conjugate pairs. When finding a conjugate acid or base, it is important to look at the reactants of the chemical equation. In this case, the reactants are the acids and bases, the acid corresponds to the conjugate base on the product side of the chemical equation. To identify the conjugate acid, look for the pair of compounds that are related; the acid–base reaction can be viewed in a before and after sense. The before is the reactant side of the after is the product side of the equation; the conjugate acid in the after side of an equation gains a hydrogen ion, so in the before side of the equation the compound that has one less hydrogen ion of the conjugate acid is the base.
The conjugate base in the after side of the equation lost a hydrogen ion, so in the before side of the equation, the compound that has one more hydrogen ion of the conjugate base is the acid. Consider the following acid–base reaction: HNO3 + H2O → H3O+ + NO−3Nitric acid is an acid because it donates a proton to the water molecule and its conjugate base is nitrate; the water molecule acts as a base because it receives the Hydrogen Proton and its conjugate acid is the hydronium ion. One use of conjugate acids and bases lies in buffering systems. In a buffer, a weak acid and its conjugate base, or a weak base and its conjugate acid, are used in order to limit the pH change during a titration process. Buffers have both non-organic chemical applications. For example, besides buffers being used in lab processes, our blood acts as a buffer to maintain pH; the most important buffer in our bloodstream is the carbonic acid-bicarbonate buffer, which prevents drastic pH changes when CO2 is introduced. This functions as such: CO 2 + H 2 O ↽ − − ⇀ H 2 CO 3 ↽
Restriction of Hazardous Substances Directive
The Restriction of Hazardous Substances Directive 2002/95/EC, short for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment, was adopted in February 2003 by the European Union. The RoHS 1 directive took effect on 1 July 2006, is required to be enforced and became a law in each member state; this directive restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is linked with the Waste Electrical and Electronic Equipment Directive 2002/96/EC which sets collection and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic electronic waste. In speech, RoHS is spelled out, or pronounced, or, refers to the EU standard, unless otherwise qualified; each European Union member state will adopt its own enforcement and implementation policies using the directive as a guide. RoHS is referred to as the "lead-free directive," but it restricts the use of the following ten substances: Lead Mercury Cadmium Hexavalent chromium Polybrominated biphenyls Polybrominated diphenyl ether Bis phthalate Butyl benzyl phthalate Dibutyl phthalate Diisobutyl phthalate DEHP, BBP, DBP and DIBP were added as part of DIRECTIVE 2015/863, published on 31 March 2015.
PBB and PBDE are flame retardants used in several plastics. Hexavalent chromium is used in chrome plating, chromate coatings and primers, in chromic acid; the maximum permitted concentrations in non-exempt products are 1000 ppm by weight. The restrictions are on each homogeneous material in the product, which means that the limits do not apply to the weight of the finished product, or to a component, but to any single substance that could be separated mechanically—for example, the sheath on a cable or the tinning on a component lead; as an example, a radio is composed of a case, washers, a circuit board, etc. The screws and case may each be made of homogenous materials, but the other components comprise multiple sub-components of many different types of material. For instance, a circuit board is composed of a bare PCB, ICs, capacitors, etc. A switch is composed of a case, a lever, a spring, pins, etc. each of which may be made of different materials. A contact might be composed of a copper strip with a surface coating.
A speaker is composed of a permanent magnet, copper wire, etc. Everything that can be identified as a homogeneous material must meet the limit. So if it turns out that the case was made of plastic with 2,300 ppm PBB used as a flame retardant the entire radio would fail the requirements of the directive. In an effort to close RoHS 1 loopholes, in May 2006 the European Commission was asked to review two excluded product categories for future inclusion in the products that must fall into RoHS compliance. In addition the commission entertains requests for deadline extensions or for exclusions by substance categories, substance location or weight. New legislation was published in the official journal in July 2011. Note that batteries are not included within the scope of RoHS. However, in Europe, batteries are under the European Commission's 1991 Battery Directive, increased in scope and approved in the form of the new battery directive, version 2003/0282 COD, which will be official when submitted to and published in the EU's Official Journal.
While the first Battery Directive addressed possible trade barrier issues brought about by disparate European member states' implementation, the new directive more explicitly highlights improving and protecting the environment from the negative effects of the waste contained in batteries. It contains a programme for more ambitious recycling of industrial and consumer batteries increasing the rate of manufacturer-provided collection sites to 45% by 2016, it sets limits of 5 ppm mercury and 20 ppm cadmium to batteries except those used in medical, emergency, or portable power-tool devices. Though not setting quantitative limits on quantities of lead, lead–acid and nickel–cadmium in batteries, it cites a need to restrict these substances and provide for recycling up to 75% of batteries with these substances. There are provisions for marking the batteries with symbols in regard to metal content and recycling collection information; the directive applies to equipment. The following numeric categories apply: Large household appliances Small household appliances IT & telecommunications equipment Consumer equipment Lighting equipment – including light bulbs Electronic and electrical tools Toys and sports equipment Medical devices Monitoring and control instruments Automatic dispensers Semiconductor devicesIt does not apply to fixed industrial plant and tools.
Compliance is the responsibility of the company that puts the product on the market, as defined in the Directive. Of course, given the fact that the regulation is applied at the homogeneous material level, data on substance concentrations needs to be transferred through the supply chain to the final producer. An IPC standard has been developed and published to facilitate this data exchange, IPC-1752. It
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, can be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur; the substance involved in a chemical reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, they yield one or more products, which have properties different from the reactants. Reactions consist of a sequence of individual sub-steps, the so-called elementary reactions, the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium. Reactions that proceed in the forward direction to approach equilibrium are described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of free energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product. In biochemistry, a consecutive series of chemical reactions form metabolic pathways; these reactions are catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a cell.
The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, reactions between elementary particles, as described by quantum field theory. Chemical reactions such as combustion in fire and the reduction of ores to metals were known since antiquity. Initial theories of transformation of materials were developed by Greek philosophers, such as the Four-Element Theory of Empedocles stating that any substance is composed of the four basic elements – fire, water and earth. In the Middle Ages, chemical transformations were studied by Alchemists, they attempted, in particular, to convert lead into gold, for which purpose they used reactions of lead and lead-copper alloys with sulfur. The production of chemical substances that do not occur in nature has long been tried, such as the synthesis of sulfuric and nitric acids attributed to the controversial alchemist Jābir ibn Hayyān; the process involved heating of sulfate and nitrate minerals such as copper sulfate and saltpeter.
In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid and sodium chloride. With the development of the lead chamber process in 1746 and the Leblanc process, allowing large-scale production of sulfuric acid and sodium carbonate chemical reactions became implemented into the industry. Further optimization of sulfuric acid technology resulted in the contact process in the 1880s, the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, Isaac Newton tried to establish theories of the experimentally observed chemical transformations; the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of a fire-like element called "phlogiston", contained within combustible bodies and released during combustion; this proved to be false in 1785 by Antoine Lavoisier who found the correct explanation of the combustion as reaction with oxygen from the air.
Joseph Louis Gay-Lussac recognized in 1808 that gases always react in a certain relationship with each other. Based on this idea and the atomic theory of John Dalton, Joseph Proust had developed the law of definite proportions, which resulted in the concepts of stoichiometry and chemical equations. Regarding the organic chemistry, it was long believed that compounds obtained from living organisms were too complex to be obtained synthetically. According to the concept of vitalism, organic matter was endowed with a "vital force" and distinguished from inorganic materials; this separation was ended however by the synthesis of urea from inorganic precursors by Friedrich Wöhler in 1828. Other chemists who brought major contributions to organic chemistry include Alexander William Williamson with his synthesis of ethers and Christopher Kelk Ingold, among many discoveries, established the mechanisms of substitution reactions. Chemical equations are used to graphically illustrate chemical reactions, they consist of chemical or structural formulas of the reactants on the left and those of the products on the right.
They are separated by an arrow which indicates the type of the reaction.
Tasmania is an island state of Australia. It is located 240 km to the south of the Australian mainland, separated by Bass Strait; the state encompasses the main island of Tasmania, the 26th-largest island in the world, the surrounding 334 islands. The state has a population of around 526,700 as of March 2018. Just over forty percent of the population resides in the Greater Hobart precinct, which forms the metropolitan area of the state capital and largest city, Hobart. Tasmania's area is 68,401 km2, of which the main island covers 64,519 km2, it is promoted as a natural state, protected areas of Tasmania cover about 42% of its land area, which includes national parks and World Heritage Sites. Tasmania was the founding place of the first environmental political party in the world; the island is believed to have been occupied by indigenous peoples for 30,000 years before British colonisation. It is thought Aboriginal Tasmanians were separated from the mainland Aboriginal groups about 10,000 years ago when the sea rose to form Bass Strait.
The Aboriginal population is estimated to have been between 3,000 and 7,000 at the time of colonisation, but was wiped out within 30 years by a combination of violent guerrilla conflict with settlers known as the "Black War", intertribal conflict, from the late 1820s, the spread of infectious diseases to which they had no immunity. The conflict, which peaked between 1825 and 1831, led to more than three years of martial law, cost the lives of 1,100 Aboriginals and settlers; the island was permanently settled by Europeans in 1803 as a penal settlement of the British Empire to prevent claims to the land by the First French Empire during the Napoleonic Wars. The island was part of the Colony of New South Wales but became a separate, self-governing colony under the name Van Diemen's Land in 1825. 75,000 convicts were sent to Van Diemen's Land before transportation ceased in 1853. In 1854 the present Constitution of Tasmania was passed, the following year the colony received permission to change its name to Tasmania.
In 1901 it became a state through the process of the Federation of Australia. The state is named after Dutch explorer Abel Tasman, who made the first reported European sighting of the island on 24 November 1642. Tasman named the island Anthony van Diemen's Land after his sponsor Anthony van Diemen, the Governor of the Dutch East Indies; the name was shortened to Van Diemen's Land by the British. It was renamed Tasmania in honour of its first European discoverer on 1 January 1856. Tasmania was sometimes referred to as "Dervon," as mentioned in the Jerilderie Letter written by the notorious Australian bushranger Ned Kelly in 1879; the colloquial expression for the state is "Tassie". Tasmania is colloquially shortened to "Tas," when used in business names and website addresses. TAS is the Australia Post abbreviation for the state; the reconstructed Palawa kani language name for Tasmania is Lutriwita. The island was adjoined to the mainland of Australia until the end of the last glacial period about 10,000 years ago.
Much of the island is composed of Jurassic dolerite intrusions through other rock types, sometimes forming large columnar joints. Tasmania has the world's largest areas of dolerite, with many distinctive mountains and cliffs formed from this rock type; the central plateau and the southeast portions of the island are dolerites. Mount Wellington above Hobart is a good example. In the southern midlands as far south as Hobart, the dolerite is underlaid by sandstone and similar sedimentary stones. In the southwest, Precambrian quartzites were formed from ancient sea sediments and form strikingly sharp ridges and ranges, such as Federation Peak or Frenchmans Cap. In the northeast and east, continental granites can be seen, such as at Freycinet, similar to coastal granites on mainland Australia. In the northwest and west, mineral-rich volcanic rock can be seen at Mount Read near Rosebery, or at Mount Lyell near Queenstown. Present in the south and northwest is limestone with caves; the quartzite and dolerite areas in the higher mountains show evidence of glaciation, much of Australia's glaciated landscape is found on the Central Plateau and the Southwest.
Cradle Mountain, another dolerite peak, for example, was a nunatak. The combination of these different rock types contributes to scenery, distinct from any other region of the world. In the far southwest corner of the state, the geology is wholly quartzite, which gives the mountains the false impression of having snow-capped peaks year round. Evidence indicates the presence of Aborigines in Tasmania about 42,000 years ago. Rising sea levels cut Tasmania off from mainland Australia about 10,000 years ago and by the time of European contact, the Aboriginal people in Tasmania had nine major nations or ethnic groups. At the time of the British occupation and colonisation in 1803, the indigenous population was estimated at between 3,000 and 10,000. Historian Lyndall Ryan's analysis of population studies led her to conclude that there were about 7,000 spread throughout the island's nine nations. J. B. Plomley and Rhys Jones, settled on a figure of 3,000 to 4,000, they engaged in fire-stick farming, hunted game including kangaroo and wallabies, caught seals, mutton-birds and fish and lived as nine separate "nations" on the island, which they knew as "Trouwunna".
The first reported sighting of Tasmania by a European was on 24 November 1642 by Dutch explorer Abel Tasman, who landed at today's Blackman Bay. More than a century in 1772, a French expedition le
Heavy metals are defined as metals with high densities, atomic weights, or atomic numbers. The criteria used, whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would be more concerned with chemical behaviour. More specific definitions have been published, but none of these have been accepted; the definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements. Despite this lack of agreement, the term is used in science. A density of more than 5 g/cm3 is sometimes quoted as a used criterion and is used in the body of this article; the earliest known metals—common metals such as iron and tin, precious metals such as silver and platinum—are heavy metals. From 1809 onwards, light metals, such as magnesium and titanium, were discovered, as well as less well-known heavy metals including gallium and hafnium.
Some heavy metals are either essential nutrients, or harmless, but can be toxic in larger amounts or certain forms. Other heavy metals, such as cadmium and lead, are poisonous. Potential sources of heavy metal poisoning include mining, industrial wastes, agricultural runoff, occupational exposure and treated timber. Physical and chemical characterisations of heavy metals need to be treated with caution, as the metals involved are not always defined; as well as being dense, heavy metals tend to be less reactive than lighter metals and have much less soluble sulfides and hydroxides. While it is easy to distinguish a heavy metal such as tungsten from a lighter metal such as sodium, a few heavy metals, such as zinc and lead, have some of the characteristics of lighter metals, lighter metals such as beryllium and titanium, have some of the characteristics of heavier metals. Heavy metals are scarce in the Earth's crust but are present in many aspects of modern life, they are used in, for example, golf clubs, antiseptics, self-cleaning ovens, solar panels, mobile phones, particle accelerators.
There is no agreed criterion-based definition of a heavy metal. Different meanings may be attached depending on the context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, a chemist would be more concerned with chemical behaviour. Density criteria range from above 3.5 g/cm3 to above 7 g/cm3. Atomic weight definitions can range from greater than sodium. Atomic numbers of heavy metals are given as greater than 20. Definitions based on atomic number have been criticised for including metals with low densities. For example, rubidium in group 1 of the periodic table has an atomic number of 37 but a density of only 1.532 g/cm3, below the threshold figure used by other authors. The same problem may occur with atomic weight based definitions; the United States Pharmacopeia includes a test for heavy metals that involves precipitating metallic impurities as their coloured sulfides." In 1997, Stephen Hawkes, a chemistry professor writing in the context of fifty years' experience with the term, said it applied to "metals with insoluble sulfides and hydroxides, whose salts produce colored solutions in water and whose complexes are colored".
On the basis of the metals he had seen referred to as heavy metals, he suggested it would useful to define them as all the metals in periodic table columns 3 to 16 that are in row 4 or greater, in other words, the transition metals and post-transition metals. The lanthanides satisfy Hawkes' three-part description. In biochemistry, heavy metals are sometimes defined—on the basis of the Lewis acid behaviour of their ions in aqueous solution—as class B and borderline metals. In this scheme, class A metal ions prefer oxygen donors. Class A metals, which tend to have low electronegativity and form bonds with large ionic character, are the alkali and alkaline earths, the group 3 metals, the lanthanides and actinides. Class B metals, which tend to have higher electronegativity and form bonds with considerable covalent character, are the heavier transition and post-transition metals. Borderline metals comprise the lighter transition and post-transition metals; the distinction between the class A metals and the other two categories is sharp.
A cited proposal to use these classification categories instead of the more evocative name heavy metal has not been adopted. A density of more than 5 g/cm3 is sometimes mentioned as a common heavy metal defining factor and, in the absence of a unanimous definition, is used to populate this list and guide the remainder of the article. Metalloids meeting the applicable criteria–arsenic and antimony for example—are sometimes counted as heavy metals in environmental chemistry, as is the case here. Selenium is include
Chrome yellow is lead chromate. It occurs as the mineral crocoite but the mineral itself was never used as a pigment for paint. After the French chemist Louis Vauquelin discovered the new element chromium in 1797 lead chromate was synthesized in the laboratory and its use as a pigment began in the second decade of the nineteenth century. Chrome yellow had been produced by mixing solutions of lead nitrate and potassium chromate and filtering off the lead chromate precipitate; because the pigment tends to react with hydrogen sulfide and darken on exposure to air over time, forming lead sulfide, it contains lead, a toxic, heavy metal, the toxic and carcinogenic chromate as well it was replaced by another pigment, cadmium yellow. Darkening may occur as well by reduction with sulfur dioxide. Good quality pigments have been coated to inhibit contact with gases; the first recorded use of chrome yellow as a color name in English was in 1818. The Piper J-3 Cub aircraft had chrome yellow as its standard overall color called "Cub Yellow" or "Lock Haven Yellow" in aviation circles, from the Piper factory that existed in Lock Haven, where it was made in the 1930s and during World War II.
List of colors List of inorganic pigments School bus yellow Kühn, H. and Curran, M. Chrome Yellow and Other Chromate Pigments, in Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 1, L. Feller, Ed. Cambridge University Press, London 1986 Chrome yellow, Colourlex Pichon, A. Pigment degradation: Chrome yellow’s darker side. Nature Chemistry, 5, 2013, 897–897. Doi:10.1038/nchem.1789
Sodium carbonate, Na2CO3, is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, water-soluble salts. All forms have a alkaline taste and give moderately alkaline solutions in water, it was extracted from the ashes of plants growing in sodium-rich soils. Because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash", it is produced in large quantities from sodium limestone by the Solvay process. Sodium carbonate is obtained as three different hydrates and as the anhydrous salt: sodium carbonate decahydrate, Na2CO3·10H2O, which effloresces to form the monohydrate. Sodium carbonate heptahydrate, Na2CO3·7H2O. Sodium carbonate monohydrate, Na2CO3·H2O. Known as crystal carbonate. Anhydrous sodium carbonate known as calcined soda, is formed by heating the hydrates, it is formed when sodium hydrogen carbonate is heated e.g. in the final step of the Solvay process. The decahydrate is formed from water solutions crystallizing in the temperature range -2.1 to +32.0 C, the heptahydrate in the narrow range 32.0 to 35.4 C and above this temperature the monohydrate forms.
In dry air the decahydrate and heptahydrate lose water to give the monohydrate. Other hydrates have been reported. In terms of its largest applications, sodium carbonate is used in the manufacture of glass, rayon and detergents. Sodium carbonate serves as a flux for silica, lowering the melting point of the mixture to something achievable without special materials; this "soda glass" is mildly water-soluble, so some calcium carbonate is added to the melt mixture to make the glass produced insoluble. Bottle and window glass is made by melting such mixtures of sodium carbonate, calcium carbonate, silica sand; when these materials are heated, the carbonates release carbon dioxide. In this way, sodium carbonate is a source of sodium oxide. Soda lime glass has been the most common form of glass for centuries. Sodium carbonate is used to soften water by removing Mg2+ and Ca2+; these ions form insoluble solid precipitates upon treatment with carbonate ions: Ca2+ + CO32- → CaCO3Sodium carbonate is an inexpensive and water-soluble source of carbonate ions.
Sodium carbonate is a food additive used as an acidity regulator, anticaking agent, raising agent, stabilizer. It is one of the components of kansui, a solution of alkaline salts used to give ramen noodles their characteristic flavor and texture, it is used in the production of snus to stabilize the pH of the final product. Sodium carbonate is used in the production of sherbet powder; the cooling and fizzing sensation results from the endothermic reaction between sodium carbonate and a weak acid citric acid, releasing carbon dioxide gas, which occurs when the sherbet is moistened by saliva. In China, it is used to replace lye-water in the crust of traditional Cantonese moon cakes, in many other Chinese steamed buns and noodles. In cooking, it is sometimes used in place of sodium hydroxide for lyeing with German pretzels and lye rolls; these dishes are treated with a solution of an alkaline substance to change the pH of the surface of the food and improve browning. Sodium carbonate is used as a strong base in various fields.
As a common alkali, it is preferred in many chemical processes because it is cheaper than NaOH and far safer to handle. Its mildness recommends its use in domestic applications. For example, it is used as a pH regulator to maintain stable alkaline conditions necessary for the action of the majority of photographic film developing agents. For example, it is a common additive in swimming pools and aquarium water to maintain a desired pH and carbonate hardness. In dyeing with fiber-reactive dyes, sodium carbonate is used to ensure proper chemical bonding of the dye with cellulose fibers before dyeing, mixed with the dye, or after dyeing. Sodium bicarbonate or baking soda a component in fire extinguishers, is generated from sodium carbonate. Although NaHCO3 is itself an intermediate product of the Solvay process, the heating needed to remove the ammonia that contaminates it decomposes some NaHCO3, making it more economic to react finished Na2CO3 with CO2: Na2CO3 + CO2 + H2O → 2NaHCO3In a related reaction, sodium carbonate is used to make sodium bisulphite, used for the "sulfite" method of separating lignin from cellulose.
This reaction is exploited for removing sulphur dioxide from flue gases in power stations: Na2CO3 + SO2 + H2O → NaHCO3 + NaHSO3This application has become more common where stations have to meet stringent emission controls. Sodium carbonate is used by the cotton industry to neutralize the sulfuric acid needed for acid delinting of fuzzy cottonseed. Sodium carbonate is used by the brick industry as a wetting agent to reduce the amount of water needed to extrude the clay. In casting, it is referred to as "bonding agent" and is used to allow wet alginate to adhere to gelled alginate. Sodium carbonate is used in toothpastes, where it acts as a foaming agent and an abrasive, to temporarily increase mouth pH; the integral enthalpy of solution of sodium carbonate is −28.1 kJ/mol for a 10% w/w aqueous solution. The Mohs hardness of sodium carbonate monohydrate is 1.3. Sodium carbonate is soluble in water, can occur nat