Metals, flame colorations

Note that some of the metals frequently encountered in simple organic compounds give characteristic flame colorations Na, yellow K, lilac through blue glass Ca, brick-red Ba, apple-green Cu, bright blue-green. Ag and Pb, no characteristic flame. 

All the alkali metals have characteristic flame colorations due to the ready excitation of the outermost electron, and this is the basis of their analytical determination by flame photometry or atomic absorption spectroscopy. The colours and principal emission (or absorption) wavelengths, X, are given below but it should be noted that these lines do not all refer to the same transition for example, the Na D-line doublet at 589.0, 589.6 nm arises from the 3s — 3p transition in Na atoms formed by reduction of Na+ in the flame, whereas the red line for lithium is associated with the short-lived species LiOH. 

The presence of incandescent solid or liquid particles in the flame will adversely affect color quality. The resulting "black body" emission of white light will enhance overall emission intensity, but the color quality will be lessened. A "washed out" color will be perceived by viewers. The use of magnesium or aluminum metal in color compositions will yield high flame temperatures and high overall intensity, but broad emission from incandescent magnesium oxide or aluminum oxide products may lower color purity. 

Another colored composition which is wickless and burns with a colored flame consists of 100 part metaldehyde, at least 5 part AN, and at least 4 parts of a mixture of chlorates and nitrates of flame-coloring metals (Ref 5)... 

Identifying patterns For three of the metal ions tested, explain how the flame color you saw relates to the lines of color you saw when you looked through the spectroscope. 

While performing the experiment, you would record the name of the solution and then the observation of the flame color. If you weren t sure of the metal ion as you were doing the experiment, you could enter it into the table by checking oxidation numbers afterward. Not only does the table organize your observations, it could also be used as a reference to determine whether a solution of some unknown composition contains one of the metal ions listed in the table. 

In addition, spectral light was used to study gases and flames colored by the addition of various metal salts and transparent liquids, as well as to monitor the effects of photochemical changes. Based on his work on spectral analysis, Scheele established that there is a difference between actions of light and heat. This line of research was subsequently to lead to the discovery of the infrared region of the spectrum in 1800 by Friedrich Wilhelm Herschel (discussed above), and the ultraviolet region in 1801 by J.W. Ritter (discussed above). It also led William Hyde Wollaston to discover the ultraviolet region of the spectrum in 1802 he referred to this discovery as chemical rays. ... 

METAL FUELS FOR COLORED FLAMES — COLOR PURITY... 

When metals are burned, they form oxides (AI2O3 and MgO) that may weaken the purity of flame color. This is because their boiling points are so high that they remain as liquid droplets and thus emit a continuous (white light) spectrum. 

Flame colors induced by different metals—spectroscopy with the naked eye... 

The vapor of certain chemical elements imparts a characteristic color to the flame of burning gas (e.g., Bunsen burner). This property is used for identifying quahtatively various metallic elements. The flame coloration is caused by electronic transitions occurring between the energy levels of the atoms of the chemical element. For a particular chemical element the flame coloration is always the same, regardless of whether the chemical element is in the free atomic state or chemically in molecules. For example, free sodium metal, sodium chloride, sodium carbonate and sodium sulfate all impart an intense yellow color to the flame (D-line of 589 nm). This yellow color is characteristic of sodium in any form, and hence can be used as a test for sodium. In the making of flame tests, chlorides of the metals are commonly used, since chlorides are more volatile than other salts. 

Rubidium is a silvery white and very soft metal that colors a flame yeUowish-violet. In chemical behavior rubidium resembles sodium and potassium and reacts violently with water. It is a widely distributed element, usually associated with other alkali metals in minerals. The rate of radioactive decay of the isotope Rb can be used in geological age determination (see Chapter 4 Geochemistry). Rubidium is found in small quantities in tea, coffee, tobacco and other plants. 

By the 17 century, elaborate displays of traditional fireworks accompanied important celebrations. In the 18 century, however, many new substances became available, materials with distinct flame colors. This opened up new possibilities for artistic fireworks. The basic phenomena of flame and color production became well established, but novel effects and novel materials still continue to be discovered. Color was given to the fire by incorporating compounds of various metals (Table 16.1). Using the names Chinese and Bengal lights retain the connection with the origin of fireworks components. 

Some of the dramatic colors seen in fireworks displays are the flame colors of some of the groups 1 and 2 metals. These colors, as we will see, are related to the electronic structures of those metal atoms. 

Lithium is presently being recovered from brines of Searles Lake, in California, and from those in Nevada. Large deposits of quadramene are found in North Carolina. The metal is produced electrolytically from the fused chloride. Lithium is silvery in appearance, much like Na and K, other members of the alkali metal series. It reacts with water, but not as vigorously as sodium. Lithium imparts a beautiful crimson color to a flame, but when the metal burns strongly, the flame is a dazzling white. 

As with other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It catches fire spontaneously on water. Potassium and its salts impart a violet color to flames. 

Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group and is the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium, and potassium. It colors a flame yellowish violet. Rubidium metal can be prepared by reducing rubidium chloride with calcium, and by a number of other methods. It must be kept under a dry mineral oil or in a vacuum or inert atmosphere. 

Strontium is softer than calcium and decomposes in water more vigorously. It does not absorb nitrogen below 380oC. It should be kept under kerosene to prevent oxidation. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares. Natural strontium is a mixture of four stable isotopes. 

FWWMR Finish. The abbreviation for fire, water, weather, and mildew resistance, FWWMR, has been used to describe treatment with a chlorinated organic metal oxide. Plasticizers, coloring pigments, fiUers, stabilizers, or fungicides usuaUy are added. However, hand, drape, flexibUity, and color of the fabric are more affected by this type of finish than by other flame retardants. Add-ons of up to 60% are required in many cases to obtain... 

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