"that it can be ignored at pH > 4. Loss of the second proton occurs in the pH range 4–8, making the ion [HCrO] a weak acid. Molecular chromic acid could in principle be made by adding chromium trioxide to water (""cf."" manufacture of sulfuric acid). but in practice the reverse reaction occurs when molecular chromic acid is dehydrated. This is what happens when concentrated sulfuric acid is added to a dichromate solution. At first the colour changes from orange (dichromate) to red (chromic acid) and then deep red crystals of chromium trioxide precipitate from the mixture, without further colour"
"Litmus Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. Litmus was used for the first time about 1300 AD by Spanish physician Arnaldus de Villa Nova. From the 16th century on, the blue dye was extracted from some lichens, especially in the Netherlands. Litmus can be found in different species of lichens. The dyes are extracted from such species as ""Roccella tinctoria"" (South America), ""Roccella fuciformis"" (Angola and Madagascar), ""Roccella pygmaea"" (Algeria), ""Roccella phycopsis"","
"a shorter wavelength. This is what causes the molecule to appear red in the presence of an acid. Erythrolitmin Erythrolitmin (also called erythrolein) is the active ingredient extracted from the Litmus lichen, used in chemistry as a pH indicator. The erythrolitmin molecule is related to the orceins, and consists essentially of several phenoxazone and orcinol residues. The intense coloring of the molecule is generated by the absorption of specific wavelengths of light by the pi bonds. These bonds are ordinarily excited by light in the orange region of the spectrum, causing the molecule to appear blue. When the molecule interacts"
"and ammonium chloride in sulfuric acid is used. In the presence of nitrates, diphenylamine is oxidized, giving a blue coloration. This reaction has been used to test for organic nitrates as well., and has found use in gunshot residue kits detecting nitroglycerine and nitrocellulose. The nitrate ion can easily be identified by heating copper turnings along with concentrated sulphuric acid. Brown, pungent effervescence is observed which turns blue litmus red. Here sulphuric acid reacts with the nitrate ion to form nitric acid. Nitric acid then reacts with the copper turnings to form nitric oxide. Nitric oxide is thus oxidised to"
"when in a pH neutral environment, but become colored when dissolved in a melt and exposed to an acidic environment. Leuco dyes, in general, provide little color when melted unless they are melted in conjunction with one or more organic acids. Examples of organic acids suitable for thermochromic papers are phenols such as Bisphenol A (BPA) and Bisphenol S (BPS). Other suitable acidic materials are sulfonyl ureas such as BTUM and Pergafast 201. Zinc salts of substituted salicylic acids, such as zinc di-tert-butylsalicylate have also been commercially used as developers. A leuco dye and a developer, when melted together, are"
"cheaper replacement for saffron). Turmeric paper, also called curcuma paper or in German literature, ""Curcumapapier"", is paper steeped in a tincture of turmeric and allowed to dry. It is used in chemical analysis as an indicator for acidity and alkalinity. The paper is yellow in acidic and neutral solutions and turns brown to reddish-brown in alkaline solutions, with transition between pH of 7.4 and 9.2. Turmeric grows wild in the forests of South and Southeast Asia, where it is collected for use in Indian traditional medicine (Siddha or Ayurveda). In Eastern India, the plant is used as one of the"
"give elemental sulfur: The sequential oxidation of sulfur dioxide followed by its hydration is used in the production of sulfuric acid. Sulfur dioxide is one of the few common acidic yet reducing gases. It turns moist litmus pink (being acidic), then white (due to its bleaching effect). It may be identified by bubbling it through a dichromate solution, turning the solution from orange to green (Cr (aq)). It can also reduce ferric ions to ferrous. Sulfur dioxide can react with certain 1,3-dienes in a cheletropic reaction to form cyclic sulfones. This reaction is exploited on an industrial scale for the"
"opens, and its absorption spectrum shifts drastically, therefore it becomes deeply violet. In this case the apparent thermochromism is in fact halochromism. The dyes most commonly used are spirolactones, fluorans, spiropyrans, and fulgides. The acids include bisphenol A, parabens, 1,2,3-triazole derivates, and 4-hydroxycoumarin and act as proton donors, changing the dye molecule between its leuco form and its protonated colored form; stronger acids would make the change irreversible. Leuco dyes have less accurate temperature response than liquid crystals. They are suitable for general indicators of approximate temperature (""too cool"", ""too hot"", ""about OK""), or for various novelty items. They are"
"Lithol Rubine BK Lithol Rubine BK is a reddish synthetic azo dye. It has the appearance of a red powder and magenta when printed. It is slightly soluble in hot water, insoluble in cold water, and insoluble in ethanol. When dissolved in dimethylformamide, its absorption maximum lies at about 442 nm. It is usually supplied as a calcium salt. It is prepared by azo coupling with 3-hydroxy-2-naphthoic acid. It is used to dye plastics, paints, printing inks, and for textile printing. It is normally used as a standard magenta in the three and four color printing processes. When used as"
"acid, the print is washed in 1% potassium metabisulfite after proper development in water. Interested individuals should read up on the process before attempting, as the chromic acids are very dangerous to work with. The mechanics of the gum portion is not entirely known; what occurs is the exposed gum is hardened and becomes water-insoluble. Upon washing, the unexposed portions wash away, leaving the white paper exposed. The technique is related to platinum printing. Gum over platinum Gum over platinum is a historical chemical photographic process, which was commonly used in art photography. It is a very complex process, in"
"Acid-free paper Acid-free paper is paper that if infused in water yields a neutral or basic pH (7 or slightly greater). It can be made from any cellulose fiber as long as the active acid pulp is eliminated during processing. It is also lignin- and sulfur-free. Acid-free paper addresses the problem of preserving documents and artwork for long periods. Paper made from wood-based pulp that has not had its lignin removed turns yellow, becomes brittle, and deteriorates over time. When exposed to light and/or heat, the molecules in the acidic paper will break down even faster. Acidic wood-pulp paper became"
"Lithium nitride Lithium nitride is a compound with the formula LiN. It is the only stable alkali metal nitride. The solid is a red or purple color and has a high melting point. Lithium nitride is prepared by direct combination of elemental lithium with nitrogen gas: Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid sodium metal can be treated with N. Lithium nitride reacts violently with water to produce ammonia: ""alpha""-LiN (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers, one sheet has"
"a food dye, it has E number E180. It is used to color cheese rind as well as a component in some lip balms. Lithol Rubine BK Lithol Rubine BK is a reddish synthetic azo dye. It has the appearance of a red powder and magenta when printed. It is slightly soluble in hot water, insoluble in cold water, and insoluble in ethanol. When dissolved in dimethylformamide, its absorption maximum lies at about 442 nm. It is usually supplied as a calcium salt. It is prepared by azo coupling with 3-hydroxy-2-naphthoic acid. It is used to dye plastics, paints, printing"
"Erythrolitmin Erythrolitmin (also called erythrolein) is the active ingredient extracted from the Litmus lichen, used in chemistry as a pH indicator. The erythrolitmin molecule is related to the orceins, and consists essentially of several phenoxazone and orcinol residues. The intense coloring of the molecule is generated by the absorption of specific wavelengths of light by the pi bonds. These bonds are ordinarily excited by light in the orange region of the spectrum, causing the molecule to appear blue. When the molecule interacts with protons from an acid the bonds become harder to excite and thus absorb green light which has"
"be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than"
"Styphnic acid Styphnic acid (from Greek ""stryphnos"" ""astringent""), or 2,4,6-trinitro-1,3-benzenediol, is a yellow astringent acid that forms hexagonal crystals. It is used in the manufacture of dyes, pigments, inks, medicines, and explosives such as lead styphnate. It is itself a low sensitivity explosive, similar to picric acid, but explodes upon rapid heating. It may be prepared by the nitration of resorcinol with a mixture of nitric and sulfuric acid. This compound is an example of a trinitrophenol. Like picric acid, it is a moderately strong acid, capable of displacing carbon dioxide from solutions of sodium carbonate, for example. It may"
"Each lobe measures between in width, and lobes are overlapping. The lichen's medulla and soredia react positively with potassium hydroxide (K), turning red-orange. They react positively with para-phenylenediamene (Pd) as well, also turning orange. The lichen does not fluoresce in ultraviolet light. ""Parmelia sulcata"" is a common species throughout much of the world, found from temperate to cold regions of both the Northern and Southern Hemispheres. This species can be used to make dyes, producing a reddish-brown color. Indigenous people in North America used the lichen medicinally. The Métis peoples rubbed it on the gums of teething babies, while the"
"in a colour change to greyish-green, aniline causes a lavender to reddish-brown colour, and phenol a purplish pink to reddish brown. On the cap cuticle, nitric acid causes an orange-salmon colour, sulphuric acid creates orange-red, ammonia usually makes brown, and a potassium hydroxide solution usually makes orange. Italian cook and author Antonio Carluccio reports this is one of the most common fungi brought to him to identify, having been mistaken for an edible species. Young specimens can be confused with many edible boletes, though as the pores become more pink the species becomes easier to identify. Some guidebooks advocate tasting"
"Many lichens produce secondary compounds, including pigments that reduce harmful amounts of sunlight and powerful toxins that reduce herbivory or kill bacteria. These compounds are very useful for lichen identification, and have had economic importance as dyes such as cudbear or primitive antibiotics. The pH indicator (indicated acidic or basic) in the litmus test is a dye extracted from the lichen ""Roccella tinctoria"" by boiling. In the Highlands of Scotland, traditional dyes for Harris tweed and other traditional cloths were made from lichens including the orange ""Xanthoria parietina"" and the grey foliaceous ""Parmelia saxatilis"" common on rocks known as ""crottle""."
"alkaline material the name """"lithion""/""lithina"""", from the Greek word ""λιθoς"" (transliterated as ""lithos"", meaning ""stone""), to reflect its discovery in a solid mineral, as opposed to potassium, which had been discovered in plant ashes, and sodium, which was known partly for its high abundance in animal blood. He named the metal inside the material ""lithium"". Arfwedson later showed that this same element was present in the minerals spodumene and lepidolite. In 1818, Christian Gmelin was the first to observe that lithium salts give a bright red color to flame. However, both Arfwedson and Gmelin tried and failed to isolate the"
"to 2.5 micrograms and a concentration of 1 in 25,000 parts. Devarda's alloy (Copper/Aluminium/Zinc) is a reducing agent. When reacted with nitrate in sodium hydroxide solution, ammonia is liberated. The ammonia formed may be detected by its characteristic odor, and by damp red litmus paper's turning blue, signalling that it is an alkali — very few gases other than ammonia evolved from wet chemistry are alkaline. Aluminium is the reducing agent in this reaction that will occur. Diphenylamine may be used as a wet chemical test for the presence of the nitrate ion. In this test, a solution of diphenylamine"
"atmospheric pollutants, although this can be reversed. Lead is not a traditional pigment in water mediums, as zinc is superior for works on paper, as is calcium hydroxide (slaked lime) for frescos. Lead-based paints, when used on paper, often cause the work to become discolored after long periods of time; the paint's lead carbonate reacts with hydrogen sulfide in the air and with acids, which often come from fingerprints. Paint manufacturers have replaced white lead with a less toxic substitute, titanium white (based on the pigment titanium dioxide), which was first used in paints in the 19th century. Titanium dioxide"
"is oxidized to the coloured cationic form: (A typical oxidizing agent is manganese dioxide). When dissolved in water, the dye has a blue-violet colour with an absorbance maximum at 590 nm and an extinction coefficient of 87,000 M cm. The colour of the dye depends on the acidity of the solution. At a pH of +1.0, the dye is green with absorption maxima at 420 nm and 620 nm, while in a strongly acidic solution (pH −1.0), the dye is yellow with an absorption maximum at 420 nm. The different colours are a result of the different charged states of"
"involves ""digesting"" molybdenum sulfide with nitric acid to form molybdic acid, which is then mixed with tin filings and a little muriatic acid (HCl). This is evaporated and heated with alumina. A 1955 paper states that molybdenum blue is unstable and is not used commercially as a pigment. The chemistry of these pigments has not been investigated. Molybdenum blue Molybdenum blue is a term applied to: The ""heteropoly-molybdenum blues"", are used extensively in analytical chemistry and as catalysts. The formation of ""isopoly-molybdenum blues"" which are intense blue has been used as a sensitive test for reducing reagents. They have recently"
"Tolonium chloride Tolonium chloride (INN, also known as toluidine blue or TBO) is a blue cationic (basic) dye used in histology and sometimes clinically. Toluidine blue solution is used in testing for lignin, a complex organic molecule that bonds to cellulose fibres and strengthens and hardens the cell walls in plants. A positive toluidine blue test causes the solution to turn from blue to pink. A similar test can be performed with phloroglucinol-HCl solution, which turns red. Toluidine Blue is often used to identify mast cells, by virtue of the heparin in their cytoplasmic granules. It is also used to"
"to be higher at c. 68.5 kJ/mol. The alpha form is a semiconductor with band gap of c. 2.1 eV. Reaction with hydrogen at under 300 °C (0.5 MPa pressure) produces lithium hydride and lithium amide. Lithium nitride has been investigated as a storage medium for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved. Lithium nitride Lithium nitride is a compound with the formula LiN. It is the only stable alkali metal nitride. The solid is a red or purple color and has a high melting point."
"or blue during pickling and cooking. Under these conditions (""i.e."" acidity, heat) the sulfur-containing compound alliinase react with common amino acids to make pyrroles, clusters of carbon-nitrogen rings. These rings can be linked together into polypyrrole molecules. Ring structures absorb particular wavelengths of light and thus appear colored. The two-pyrrole molecule looks red, the three-pyrrole molecule looks blue and the four-pyrrole molecule looks green (like chlorophyll, a tetrapyrrole). Like chlorophyll, the pyrrole pigments are safe to eat. Upon cutting, similar to a color change in onion caused by reactions of amino acids with sulfur compounds, garlic can turn green. Garlic"
"reduced and becomes colorless, the resultant increase in light transmittance can be measured using a spectrophotometer. DCPIP can also be used as an indicator for vitamin C. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid. This reaction is a redox reaction: vitamin C (ascorbic acid) is oxidized to dehydroascorbic acid, and DCPIP is reduced to the colorless compound DCPIPH In this titration, when all the ascorbic acid in the solution has been used up, there will not be any"
"change of color. At low temperatures, the mixture is a solid. The weak acid forms a colored complex with the leuco dye by causing the lactone ring in the center of the dye molecule to open. At high temperatures, above 24–27 °C, the solvent melts and the ammonium salt dissociates, allowing it to react with the weak acid. This reaction increases the pH, which leads to closing of the lactone ring of the dye to convert it to its colorless (leuco) form. Therefore, at the low temperature the color of the shirt is the combination of the color of the"
"Leuco dye A leuco dye (from the Greek λευκός ""leukos"": white ) is a dye which can switch between two chemical forms; one of which is colorless. Reversible transformations can be caused by heat, light or pH; resulting in examples of thermochromism, photochromism and halochromism respectively. Irreversible transformations typically involve reduction or oxidation. The colorless form is sometimes referred to as the leuco form. Leuco dyes form the basis of thermal printer papers and certain pH indicators. The most common example is in applying sulfur dyes and vat dyes; with indigo being a classic case. This is characteristically purple but"
"pigments, but not always with happy results. In 1962 he donated to Harvard University a series of large murals of the Passion of Christ whose predominant colors were dark pink and deep crimson. He mixed mostly traditional colors to make the pink and crimson; synthetic ultramarine, cerulean blue, and titanium white, but he also used two new organic reds, Naphtol and Lithol. The Naphtol did well, but the Lithol slowly changed color when exposed to light. Within five years the deep pinks and reds had begun to turn light blue, and by 1979 the paintings were ruined and had to"
"with bismuth are all the same. However, the molecule is not rigid, as can be determined from the nuclear magnetic resonance spectrum that shows all methyl groups are equivalent. It is stable as a solid, but in the gas phase, when heated or in solution decomposes to trimethylbismuth. The colour is unusual for bismuth or other hypervalent pnictide compounds, which are colourless. Calculations show that the colour is due to HOMO-LUMO transition. The HOMO is ligand based, whereas the LUMO is modified by relativistically stabilised bismuth 6s orbitals. If excess methyllithium is used in production, an orange hexamethylbismuth salt, LiBi(CH),"
"samples of the wine to chromatograph paper. The paper is then rolled and placed in a jar filled with a butanol solution containing bromocresol green indicator dye for several hours. After the paper is pulled out and dried, the distance of yellow-colored ""splotches"" from the base line denotes the presence of various acids, with tartaric being closest to the baseline followed by citric, malic, and finally lactic acids near the top of the paper. A significant limitation to paper chromatography is that it will not show exactly how much malic is still remaining in the wine, with the size of"