Acid in the context of Solvent

Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types of material. As a method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today. In a number of modern variants such as microfabrication etching and photochemical milling, it is a crucial technique in modern technology, including circuit boards.

In traditional pure etching, a metal plate (usually of copper, zinc or steel) is covered with a waxy ground which is resistant to acid. The artist then scratches off the ground with a pointed etching needle where the artist wants a line to appear in the finished piece, exposing the bare metal. The échoppe, a tool with a slanted oval section, is also used for "swelling" lines. The plate is then dipped in a bath of acid, known as the mordant (French for "biting") or etchant, or has acid washed over it. The acid "bites" into the metal (it undergoes a redox reaction) to a depth depending on time and acid strength, leaving behind the drawing (as carved into the wax) on the metal plate. The remaining ground is then cleaned off the plate. For first and renewed uses the plate is inked in any chosen non-corrosive ink all over and the surface ink drained and wiped clean, leaving ink in the etched forms.

Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide (CO₂) levels exceeding 422 ppm (as of 2024). CO₂ from the atmosphere is absorbed by the oceans. This chemical reaction produces carbonic acid (H₂CO₃) which dissociates into a bicarbonate ion (HCO−3) and a hydrogen ion (H). The presence of free hydrogen ions (H) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.

A change in pH by 0.1 represents a 26% increase in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH units is equivalent to a tenfold change in hydrogen ion concentration). Sea-surface pH and carbonate saturation states vary depending on ocean depth and location. Colder and higher latitude waters are capable of absorbing more CO₂. This can cause acidity to rise, lowering the pH and carbonate saturation levels in these areas. There are several other factors that influence the atmosphere-ocean CO₂ exchange, and thus local ocean acidification. These include ocean currents and upwelling zones, proximity to large continental rivers, sea ice coverage, and atmospheric exchange with nitrogen and sulfur from fossil fuel burning and agriculture.

Lead (/lɛd/ ) is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal, denser than most common materials. Lead is soft, malleable, and has a relatively low melting point. When freshly cut, it appears shiny gray with a bluish tint, but tarnishes to dull gray on exposure to air. Lead has the highest atomic number of any stable element, and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.

Lead is a relatively unreactive post-transition metal. Its weak metallic character is shown by its amphoteric behavior: lead and lead oxides react with both acids and bases, and it tends to form covalent bonds. Lead compounds usually occur in the +2 oxidation state rather than the +4 state common in lighter members of the carbon group, with exceptions mostly limited to organolead compounds. Like the lighter members of the group, lead can bond with itself, forming chains and polyhedral structures.

The chemical industry comprises the companies and other organizations that develop and produce industrial, specialty and other chemicals. Central to the modern world economy, the chemical industry converts raw materials (oil, natural gas, air, water, metals, and minerals) into commodity chemicals for industrial and consumer products. It includes industries for petrochemicals such as polymers for plastics and synthetic fibers; inorganic chemicals such as acids and alkalis; agricultural chemicals such as fertilizers, pesticides and herbicides; and other categories such as industrial gases, speciality chemicals and pharmaceuticals.

Various professionals are involved in the chemical industry including chemical engineers, chemists and lab technicians.

Hydrogen is a chemical element; it has the symbol H and atomic number 1. It is the lightest and most abundant chemical element in the universe, constituting about 75% of all normal matter. Under standard conditions, hydrogen is a gas of diatomic molecules with the formula H₂, called dihydrogen, or sometimes hydrogen gas, molecular hydrogen, or simply hydrogen. Dihydrogen is colorless, odorless, non-toxic, and highly combustible. Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found as the gas H₂ (dihydrogen) and in molecules, such as in water and organic compounds. The most common isotope of hydrogen, H, consists of one proton, one electron, and no neutrons.

Hydrogen gas was first produced artificially in the 17th century by the reaction of acids with metals. Henry Cavendish, in 1766–1781, identified hydrogen gas as a distinct substance and discovered its property of producing water when burned: this is the origin of hydrogen's name, which means 'water-former' (from Ancient Greek: ὕδωρ, romanized: húdōr, lit. 'water', and γεννάω, gennáō, 'I bring forth'). Understanding the colors of light absorbed and emitted by hydrogen was a crucial part of the development of quantum mechanics.

A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls. Cellulose is crystalline, strong, and resistant to hydrolysis. Hemicelluloses are branched, shorter in length than cellulose, and also show a propensity to crystallize. They can be hydrolyzed by dilute acid or base as well as a myriad of hemicellulase enzymes.

Tanning, or hide tanning, is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed.

Historically, vegetable based tanning used tannin, an acidic chemical compound derived from the bark of certain trees, in the production of leather. An alternative method, developed in the 1800s, is chrome tanning, where chromium salts are used instead of natural tannins.

In chemistry, pH (/piːˈheɪtʃ/ or /piːˈeɪtʃ/; pee-HAYCH or pee-AYCH) is a logarithmic scale used to specify the acidity or basicity of aqueous solutions. Acidic solutions (solutions with higher concentrations of hydrogen (H) cations) are measured to have lower pH values than basic or alkaline solutions. While the origin of the symbol 'pH' can be traced back to its original inventor, and the 'H' refers clearly to hydrogen, the exact original meaning of the letter 'p' in pH is still disputed; it has since acquired a more general technical meaning that is used in numerous other contexts.

The pH scale is logarithmic and inversely indicates the activity of hydrogen cations in the solution

Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver in peroxisomes. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts.

Primary bile acids are those synthesized by the liver. Secondary bile acids result from bacterial actions in the colon. In humans, taurocholic acid and glycocholic acid (derivatives of cholic acid) and taurochenodeoxycholic acid and glycochenodeoxycholic acid (derivatives of chenodeoxycholic acid) are the major bile salts. The salts of their 7-alpha-dehydroxylated derivatives, deoxycholic acid and lithocholic acid, are also found, with derivatives of cholic, chenodeoxycholic and deoxycholic acids accounting for over 90% of human biliary bile acids.

A mordant or dye fixative is a substance used to set (i.e., bind) dyes on fabrics. It does this by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in cell or tissue preparations. Although mordants are still used, especially by small batch dyers, they have been largely displaced in industry by substantive dyes.

The term mordant comes from the Latin mordere, "to bite". In the past, it was thought that a mordant helped the dye "bite" onto the fiber so that it would hold fast during washing. A mordant is often a polyvalent metal ion, and one example is chromium (III). The resulting coordination complex of dye and ion is colloidal and can be either acidic or alkaline.

Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H, and an anion, A. The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated solutions.

Examples of strong acids are hydrochloric acid (HCl), perchloric acid (HClO₄), nitric acid (HNO₃) and sulfuric acid (H₂SO₄).

Cheese is a type of dairy product produced in a range of flavors, textures, and forms by coagulation of the milk protein casein. It is composed of proteins and fat from milk, usually of cows, goats or sheep, and sometimes of water buffalo. During production, milk is usually acidified and either the enzymes of rennet or bacterial enzymes with similar activity are added to cause the casein to coagulate. The solid curds are then separated from the liquid whey and pressed into finished cheese. Some cheeses have aromatic molds on the rind, the outer layer, or throughout.

Over a thousand types of cheese exist, produced in various countries. Their styles, textures and flavors depend on the origin of the milk (including the animal's diet), whether they have been pasteurised, the butterfat content, the bacteria and mold, the processing, and how long they have been aged. Herbs, spices, or wood smoke may be used as flavoring agents. Other added ingredients may include black pepper, garlic, chives or cranberries. A cheesemonger, or specialist seller of cheeses, may have expertise with selecting, purchasing, receiving, storing and ripening cheeses.

Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner. For instance, when an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton (H) and a negative ion. Dissociation is the opposite of association or recombination.

In chemistry, there are three definitions in common use of the word "base": Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.

In 1884, Svante Arrhenius proposed that a base is a substance which dissociates in aqueous solution to form hydroxide ions OH. These ions can react with hydrogen ions (H according to Arrhenius) from the dissociation of acids to form water in an acid–base reaction. A base was therefore a metal hydroxide such as NaOH or Ca(OH)₂. Such aqueous hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste bitter and change the color of pH indicators (e.g., turn red litmus paper blue).

A noble metal is a metallic chemical element that is resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, osmium, iridium) are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.

In more specialized fields of study and applications, the number of elements counted as noble metals can vary. In some contexts, the term is used only for copper, silver, and gold which have filled d-bands. In others, it is applied more broadly to any metallic or semimetallic element that does not react with a weak acid and give off hydrogen gas in the process. This broader set includes copper, mercury, technetium, rhenium, arsenic, antimony, bismuth, polonium, gold, the six platinum group metals, and silver.

The pancreas (plural pancreases, or pancreata) is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e., it has both an endocrine and a digestive exocrine function. Ninety-nine percent of the pancreas is exocrine and 1% is endocrine. As an endocrine gland, it functions mostly to regulate blood sugar levels, secreting the hormones insulin, glucagon, somatostatin and pancreatic polypeptide. As a part of the digestive system, it functions as an exocrine gland secreting pancreatic juice into the duodenum through the pancreatic duct. This juice contains bicarbonate, which neutralizes acid entering the duodenum from the stomach; and digestive enzymes, which break down carbohydrates, proteins and fats in food entering the duodenum from the stomach.

Inflammation of the pancreas is known as pancreatitis, with common causes including chronic alcohol use and gallstones. Because of its role in the regulation of blood sugar, the pancreas is also a key organ in diabetes. Pancreatic cancer can arise following chronic pancreatitis or due to other reasons, and carries a very poor prognosis, as it is often only identified after it has spread to other areas of the body.

In chemistry, an amphoteric compound (from Greek amphoteros 'both') is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.

A heath (/hiːθ/) is a shrubland habitat found mainly on free-draining infertile, acidic soils and is characterised by open, low-growing woody vegetation. Moorland is generally related to high-ground heaths with—especially in Great Britain—a cooler and damper climate.

Heaths are widespread worldwide but are rapidly disappearing and considered a rare habitat in Europe. They form extensive and highly diverse communities across Australia in humid and sub-humid areas where fire regimes with recurring burning are required for the maintenance of the heathlands. Even more diverse though less widespread heath communities occur in Southern Africa. Extensive heath communities can also be found in the Texas chaparral, New Caledonia, central Chile, and along the shores of the Mediterranean Sea. In addition to these extensive heath areas, the vegetation type is also found in scattered locations across all continents, except Antarctica.