Flame Tests for Elements

Flame Photometry. An analytical method suitable for qual and quant detn of about 70 elements, flame photometry is based on the classical flame tests for the alkali and al kaline-earth metals (Na yellow, K purple,... 

You will be familiar with this phenomenon from the atomic spectrum of the hydrogen atom, which is shown with that of some other elements in Figure 5.2, and in the characteristic flame tests for some of the metals, which emit bright colours when vaporized in a hot flame (Figure 5.3). If you need to refresh your memory, this topic is revised in the first section of the Spectroscopy CD-ROM, Introduction to Spectroscopy . 

Fire tests on building materials and structures. Part 12 Method of test for igmtability of products by direct flame impingement. Replaced BS 476 Part 5 1979 AMD 1 Fire tests on building matenals and structures. Part 20 Method for determination of the fire resistance of elements of constiaiction (general principles) (AMD 6487) dated 30 April 1990. Replaced BS 476 Part 8 1972... 

At present there is no small-scale test for predicting whether or how fast a fire will spread on a wall made of flammable or semiflammable (fire-retardant) material. The principal elements of the problem include pyrolysis of solids char-layer buildup buoyant, convective, tmbulent-boundary-layer heat transfer soot formation in the flame radiative emission from the sooty flame and the transient natme of the process (char buildup, fuel burnout, preheating of areas not yet ignited). Efforts are needed to develop computer models for these effects and to develop appropriate small-scale tests. 

Endurance burn testing generally implies that the ignited gas mixture and flow rate are adjusted to give the worst-case heating (based on temperature observations on the protected side of the element surface), that the burn continues for a specified duration, and flame penetration does not occur. Continuous flame testing implies a gas... 

Chemists used spectral analysis during the nineteenth century to analyze substances and, sometimes, to discover new elements. Another common technique for analyzing substances, often used in conjunction with spectral analysis is a flame test. One of the foremost practitioners of this technique was a chemist named Robert Bunsen. Find out why he invented his famous burner. Carry on your research to investigate other ways that chemists use spectral analysis to examine the composition of substances. Select an appropriate medium to report your findings. 

Elemental composition K 39.85%, C 24.48%, H 3.08%, 0 32.60%. Potassium may be identified by flame testing. An aqueous solution can be analyzed for potassium by flame photometry, ICP/AES, or ion selective electrode (see Potassium). Acetate anion may be measured in aqueous solution by ion chromatography under appropriate conditions. 

Emission spectroscopy utilizes the characteristic line emission from atoms as their electrons drop from the excited to the ground state. The earliest version of emission spectroscopy as applied to chemistry was the flame test, where samples of elements placed in a Bunsen burner will change the flame to different colors (sodium turns the flame yellow calcium turns it red, copper turns it green). The modem version of emission spectroscopy for the chemistry laboratory is ICP-AES. In this technique rocks are dissolved in acid or vaporized with a laser, and the sample liquid or gas is mixed with argon gas and turned into a plasma (ionized gas) by a radio frequency generator. The excited atoms in the plasma emit characteristic energies that are measured either sequentially with a monochromator and photomultiplier tube, or simultaneously with a polychrometer. The technique can analyze 60 elements in minutes. 

Elements heated by a flame glow their characteristic color. This is commonly called a flame test and is used to test for the presence of an element in a sample. When viewed through a spectroscope, the color of each element is revealed to consist of a pattern of distinct frequencies known as an atomic spectrum. 

The increased ionization energies of the heavier transition metals should not be unexpected by anyone who has had a modicum of laboratory experience with any of these elements. Although none of the coinage metals is very reactive, gold has a well-deserved reputation for being less reactive than copper or silver iron, cobalt, and nickel rust and corrode, but osmium, indium, and platinum are noble and unreaclive and therefore are used in jewelry platinum wires are the material of choice fior flame tests without contamination and one generates hydrogen with zinc and simple adds, not with mercury. 

Compounds of sodium are readily identified by the yellow color that they give to a flame. Lithium causes a carmine coloration of the flame, and potassium, rubidium, and cesium cause a violet coloration. These elements may be tested for in the presence of sodium by use of a blue filter, of cobalt glass. 

Each element s atomic emission spectrum is unique and can be used to determine if that element is part of an unknown compound. For example, when a platinum wire is dipped into a strontium nitrate solution and then inserted into a burner flame, the strontium atoms emit a characteristic red color. You can perform a series of flame tests yourself by doing the miniLAB below. 

Boron occurs in nature as part of oxygenated compounds, or borates, that have been known since ancient times for their use in glass and metal production. In 1808 Joseph-Lotiis Gay-Lussac and Louis Jacques Thenard of France and Humphry Davy of England discovered the element boron almost concurrently. Another century passed before boron was successfully isolated in pure form. Elemental boron in its amorphous form is a dark brown powder it is a yellowish-brown, hard, brittle solid in its monoclinic crystalline form. It melts at 2,300°C (4,172°E). Boron is unreactive to oxygen, water, acids, and alkalis. Boron compotmds burn yellow-green during the flame test. 

Lithium is a soft, silvery alkali metal and has the lowest density of any metal. The word lithium is derived from lithos (Greek for stone ). Johan A. Arfredson discovered lithinm in Stockholm, Sweden, in 1817. Hnmphry Davy isolated it via electrolysis in 1818. Currently, lithinm metal is generated by the electrolysis of a molten mixture of lithium chloride, LiCl, and potassium chloride, KCl. In natnre it is never found in its elemental form. Its main sources are the minerals spodumene, petalite, lepidolite, and am-blygonite. Lithium s average crustal abundance is about 18 ppm. It has the highest specific heat of any solid element and is the least reactive alkali metal toward water. Lithium bums crimson in the flame test. 

In terms of a laboratory and / or in-class demonstration setting, the emission spectra of gas tubes with hydrogen, sodium, neon, or mercury may be viewed with inexpensive diffraction gratings to illustrate identification of elements. A demonstration with flame tests of salts can further Illustrate the basis of Bohr s atomic theory. Additionally, flame tests are often employed as a part of qualitative inorganic laboratory procedures for the determination of various cations. Such lab activities or demonstrations are appropriate for middle school, high school, and undergraduate chemistry courses. 

Because the group 14 elements bond covalently, they do not lend themselves to identification through flame tests. The exception is lead, which produces a light-blue color. The carbon group elements can be identified through analysis of their physical properties (melting point, boiling point, density), emission spectra, or reactions with other chemicals. For example, tin and lead form precipitates when added to specific solutions. 

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