"alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at . Neutral litmus paper is purple. Litmus can also be prepared as an aqueous solution that functions similarly. Under acidic conditions, the solution is red, and under alkaline conditions, the solution is blue. Chemical reactions other than acid-base can also cause a color change to litmus paper. For instance, chlorine gas turns blue litmus paper white – the litmus dye is bleached, because of presence of hypochlorite ions. This reaction is irreversible, so the litmus is not acting as an indicator in this situation. The litmus mixture"
"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"","
"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"
"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"
"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"
"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"
"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"
"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."
"solution, the insoluble matter is removed by filtering, and alum is added to the clear salt solution of carminic acid to precipitate the red aluminium salt, called ""carmine lake"" or ""crimson lake"" (the ""lake"" here deriving from the word lac, referring to a resinous secretion). Purity of color is ensured by the absence of iron. Stannous chloride, citric acid, borax, or gelatin may be added to regulate the formation of the precipitate. For shades of purple, lime is added to the alum; thus, the traditional crimson color is guaranteed not only by carminic acid but also by choice of its"
"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"
"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),"
"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""."
"change. The colours are due to LMCT transitions. Chromium trioxide is the anhydride of molecular chromic acid. It is a Lewis acid and can react with a Lewis base, such as pyridine in a non-aqueous medium such as dichloromethane (Collins reagent). Dichromic acid, HCrO, (structure illustrated top right) is the fully protonated form of the dichromate ion and also can be seen as the product of adding chromium trioxide to molecular chromic acid. It is probably present in chromic acid cleaning mixtures along with the mixed chromosulfuric acid HCrSO. Chromic acid is an intermediate in chromium plating, and is also"
"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"
"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"
"rediscovered by W. Weyl in 1864. The process may be speeded up by a catalyst. Similar solutions are formed by the heavy divalent alkaline earth metals calcium, strontium, barium, as well as the divalent lanthanides, europium and ytterbium. The amide salt is quite insoluble and readily precipitates out of solution, leaving intensely coloured ammonia solutions of the alkali metals. In 1907, Charles Krause identified the colour as being due to the presence of solvated electrons, which contribute to the high electrical conductivity of these solutions. At low concentrations (below 3 M), the solution is dark blue and has ten times"
"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"
"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"
"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"
"Paper. With the advent of coloured paper stocks for office/typing/photocopier use, correction fluid manufacturers began producing their product in various colours, particularly reds, blues, and yellows, so that corrections made on these papers would be less visually invasive. The exact composition of correction fluid varies between manufacturers, but most fluids are composed of an ""opacifying agent"" and a ""solvent"" (or thinner). The opacifying agent can be composed of a mixture of titanium dioxide, latex, and other polymer resins. Thinner originally contained toluene, which was banned due to its toxicity. Later, it contained 1,1,1-trichloroethane, a skin irritant now widely banned under"
"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"
"ml at 50 °C; potassium iodide may be added to increase solubility via formation of triiodide ions, among other polyiodides. Nonpolar solvents such as hexane and carbon tetrachloride provide a higher solubility. Polar solutions, such as aqueous solutions, are brown, reflecting the role of these solvents as Lewis bases; on the other hand, nonpolar solutions are violet, the color of iodine vapour. Charge-transfer complexes form when iodine is dissolved in polar solvents, hence changing the colour. Iodine is violet when dissolved in carbon tetrachloride and saturated hydrocarbons but deep brown in alcohols and amines, solvents that form charge-transfer adducts. The"
"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"
"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"
"and ammoniacal silver solutions. It does not form a precipitate with lead acetate solution, as does the isomeric pyrocatechol. Iron(III) chloride colors its aqueous solution a dark-violet, and bromine water precipitates tribromoresorcin. These properties are what give it its use as a colouring agent for certain chromatography experiments. Sodium amalgam reduces it to dihydroresorcin, which when heated to 150 to 160 °C with concentrated barium hydroxide solution gives γ-acetylbutyric acid (D. Vorlgnder); when fused with potassium hydroxide, resorcinol yields phloroglucin, pyrocatechol, and diresorcin. It condenses with acids or acid chlorides, in the presence of dehydrating agents, to oxyketones, e.g., with"
"acid solution. This used zinc tetroxychromate dispersed in a solution of polyvinyl butyral. An 8% solution of phosphoric acid in solvent was added just before application. It was found that an easily oxidized alcohol was an essential ingredient. A thin layer of about 10–15 µm was applied, which turned from yellow to dark green when it was cured. There is still a question as to the correct mechanism. Chrome green is a mixture of Prussian blue and chrome yellow, while the chrome oxide green is chromium(III) oxide. Chromium oxides are also used as a green pigment in the field of"
"solution, white lead glycoside is formed in the presence of glucose, which becomes less soluble on cooking and turns brown. In an ammoniacal copper solution, yellow copper oxide hydrate is formed with glucose at room temperature, while red copper oxide is formed during boiling (same with dextrin, except for with an ammoniacal copper acetate solution). With Hager's reagent, glucose forms mercury oxide during boiling. An alkaline bismuth solution is used to precipitate elemental, black-brown bismuth with glucose. Glucose boiled in an ammonium molybdate solution turns the solution blue. A solution with indigo carmine and sodium carbonate destains when boiled with"
"color upon treatment of a NO-containing sample with the Griess reagent. When sulphanilic acid is added (in the picture its sulphonamide is shown instead), the nitrites form a diazonium salt. When the azo dye agent (N-alpha-naphthyl-ethylenediamine) is formed a pink colour develops. This diamine is used in place of the simpler and cheaper alpha-naphthylamine because this latter is a potent carcinogen and moreover the diamine forms a more polar and hence a much more soluble dye in acidic aqueous medium. A typical commercial Griess reagent contains 0.2% naphthylethylenediamine dihydrochloride, and 2% sulphanilamide in 5% phosphoric acid. The test was used"
"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"
"Lime (color) Lime, also called lime green, lime-green, or bitter lime, is a color that is a shade of green, so named because it is a representation of the color of the citrus fruit called limes. It is the color that is in between the web color chartreuse and yellow on the color wheel. The first recorded use of ""lime green"" as a colour name in English was in 1890. Lime (color hex code #BFFF00) is a pure spectral color at approximately 564 nanometers on the visible spectrum when plotted on the CIE chromaticity diagram. Lemon-Lime is a fluorescent chartreuse"
"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"
"Aluminium chloride Aluminium chloride (AlCl) is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron(III) chloride, giving it a yellow color. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large amounts are also used in other areas of chemical industry. The compound is often cited as a Lewis acid. It is an example of an inorganic compound that ""cracks"" at mild temperature, reversibly changing from a polymer to a monomer. AlCl adopts three different structures, depending on the"
"salt, and thymol blue monosodium salt. The colours that indicate the pH of a solution, after adding a universal indicator, are: The colours from yellow to red indicate an acidic solution, colours blue to violet indicate bases and green colour indicates that a solution is neutral. Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased. A universal indicator is collectively a mixture of indicators which show a colour change in a solution, which interprets how acidic or basic a solution is."