Chemical reactions color change

Here we see a pair of 1-hydroxyanthraquinone molecules forming a neutral 2 1 complex with a divalent metal ion. If the ion, due to electrostatic or ionic bonding interaction is fixed in the fiber, then the dye molecules are also fixed. However, since this is a chemical reaction, then changing the metal ion will change the identity of the complex, and hence, the color. Alizarin, for example, when... 

Chemical Analysis. Standard chemical analyses have been developed for determining the concentration of various ions present in the mud [23]. Test for concentration of chloride, hydroxide and calcium ions are required to fill out the API drilling mud report. The tests are based on filtration, i.e., reaction of a known volume of mud filtrate sample with a standard solution of known volume and concentration. The end of chemical reaction is usually indicated by the change of color. The concentration of the ion being tested then can be determined from a knowledge of the chemical reaction taking place [7]. 

The first instruments used by police to determine BrAc were developed in the 1930s. Until about 1980, the standard method involved adding K O , which reacts chemically with ethyl alcohol. Potassium dichromate has a bright orange-red color, whose intensity fades as reaction occurs. The extent of the color change is a measure of the amount of alcohol present. 

Like chemical reactions, electrochemical reactions are often accompanied by a change in color. For example, colorless WO3 can be reduced either chemically or electrochemically to form intensely colored compounds known as tungsten bronzes ... 

Indicators are chemical dyes that change color with a change of pH. Litmus paper and phenolphthalein are two common indicators used in acid-base reactions. They are chosen because they change color at or very near solution neutrality. Litmus paper is red in acidic solutions and blue in basic solutions. Phenolphthalein is colorless in acidic solutions and turns red in basic solutions. 

The use of the term leuco dye is a common paradox. Leuco color formers are materials that undergo controlled chemical or physical changes resulting in a shift from a colorless state to an intense color. The preparation of leuco color formers takes advantage of the very nature of colored materials themselves. The existence of extended conjugated -system in dyes is responsible for the absorption in the visible region. The chemistry of such rc-system is noted for facile reactivity, particularly to reactions such as reduction, oxidation, and hydrolysis (not hydrolytic cleavage). When n-... 

What makes indicators change color in the presence of acids and bases A color change is often the sign that a chemical reaction has occurred, and this is no exception Acid-base indicators are actually acids or bases themselves. They change colors because the acid and its conjugate base (or the base and its conjugate acid) are different colors. For example, suppose an acidic indicator, abbreviated HIn (this is not really a chemical formula, it is just a way to show an indicator that has hydrogen ions to donate), is dissolved in water. It... 

The reason the two forms of phenolphthalein are different colors is because the chemical reaction changes the shape of the phenolphthalein molecule. In other words, the molecule has a different shape under acidic conditions than it does under basic conditions. The different shapes absorb and reflect different wavelengths of light. Our eyes see different wavelengths of visible light as different colors. 

The addition of titrant from the buret must be stopped at precisely the correct moment—the moment at which the last trace of substance titrated is consumed by a fraction of a drop of titrant added, so that the correct volume can be read on the buret. That exact moment is called the equivalence point of the titration. In order to detect the equivalence point, an indicator is often used. An indicator is a substance added to the reaction flask ahead of time in order to cause a color change at or near the equivalence point, i.e., to provide a visual indication of the equivalence point. For example, the use of a chemical named phenolphthalein as an indicator for a titration in which a strong base is used as the titrant and an acid as the substance titrated would give a color change of colorless to pink in the reaction flask near the equivalence point. The color change occurring near, not exactly at, the equivalence point is usually not a concern. The reason will become clear in a later discussion. The point of a titration at which an indicator changes color, the visual indication of the equivalence point, is called the end point of the titration. As we will see, equivalence points can be determined in other ways too. 

Detection of TATP in the field has been problematic. Technologies have been developed that focus on the peroxide group. Of these tests, the most commonly available are field detection kits that rely on color changes brought on by chemical reactions. Mistral s PDK (Peroxide Detection Kit) offers chemical screening... 

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