Flame test lithium

Both LiCl and KC1 are soluble in water, but Li3P04 is not very soluble. Hence the addition of K3P04(aq) to a solution of the white solid will produce a precipitate if the white solid is LiCl, but no precipitate if the white solid is KC1. The best method is a flame test lithium gives a red color to a flame, while the potassium flame test is violet. 

Alkali metals can be qualitatively identified by flame tests. Lithium produces a red flame. Sodium produces an orange flame. Potassium, rubidium, and cesium produce violet flames. 

Because its outet valence electrons ate at a gteatet distance from its nuclei, potassium is more reactive than sodium or lithium. Even so, potassium and sodium are very similar in their chemical reactions. Due to potassiums high reactivity, it combines with many elements, particularly nonmetals. Like the other alkali metals in group 1, potassium is highly alkaline (caustic) with a relatively high pH value. When given the flame test, it produces a violet color. 

Lithium Sodium Potassium Flame tests of alkali metals... 

The correct answer is (D). Lithium salts burn bright red in flame tests. Strontium does also, but it is not listed as a choice. 

Dry test Flame colouration. Lithium compounds impart a carmine-red colour to the non-luminous Bunsen flame. The colour is masked by the presence of considerable amounts of sodium salts, but becomes visible when observed through two thicknesses of cobalt glass. 

Separation. In order to separate lithium from the other alkali metals, they are all converted into the chlorides (by evaporation with concentrated hydrochloric acid, if necessary), evaporated to dryness, and the residue extracted with absolute alcohol which dissolves the lithium chloride only. Better solvents are dry dioxan (diethylene dioxide, C4H802) and dry acetone. Upon evaporation of the extract, the residue of lithium chloride is (a) subjected to the flame test, and (b) precipitated as the phosphate after dissolution in water and adding sodium hydroxide solution. 

When electrolytic iron foil is immersed in concentrated solutions of jodium or potassium hydroxide for several weeks, and, after thorough cleaning, allowed to corrode in distilled water, the latter gradually becomes contaminated with traces of sodium or potassium salts, the bresence of which can be detected by the spectroscope or by the usual Bunsen flame test.6 Similar results have been obtained with lithium lydroxide, barium hydroxide, and with ammonia.7 It appears probable hat the alkali penetrates in minute quantities into the metal between he ferrite crystals, possibly in consequence of a certain amount of borosity in the intercrystalline cement. This theory is supported by he fact that iron which has been soaked in alkali invariably pits ... 

We have narrowed down the material used to four possibilities. It is a compound of either lithium, potassium, strontium, or calcium. Using flame tests and the wavelengths of spectroscopic analysis, you should be able to identify which of these is in the sample. 

Like the other alkali metals, cesium is a soft, silvery metal, but it appears golden if it has been exposed to small amounts of oxygen. It is not found in its metallic state in nature it is obtained as a byproduct of lithium processing of the mineral lepidolite. Its most significant ore is pollucite, and the world s largest pollucite deposit is found in Bernic Lake, Manitoba, Canada. Cesium s average crustal abundance is about 3 parts per million. Cesium is the most electropositive stable element and will ignite if exposed to air. Cesium burns blue in 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. 

Spectroscopic tests (flame spectra) the best way to employ flame tests in analysis is to resolve the light into its component tints and to identify the cations present by their characteristic sets of tints. The instrument employed to resolve light into its component colours is called a spectroscope. A simple form is shown in Fig. 2.3. It consists of a collimator A which throws a beam of parallel rays on the prism B, mounted on a turntable the telescope C through which the spectrum is observed and a tube D, which contains a scale of reference lines which may be superimposed upon the spectrum. The spectroscope is calibrated by observing the spectra of known substances, such as sodium chloride, potassium chloride, thallium chloride, and lithium chloride. The conspicuous lines are located on a graph drawn... 

The absorption and emission spectra of metals such as copper, lithium, caesium, calcium and potassium involve lines at different wavelengths to those observed in the sodium spectrum. As with sodium, a few lines in each spectrum dominate the colours of compounds of these metals in the gas flame. This is the basis of the flame tests which are used to indicate the presence of compounds of these metals (see page 195). 

In the Flame Tests for Metals movie eChapter 6.3) the characteristic color of the flame is produced by emissions at several visible wavelengths, with the most intense spectral lines dominating the color. For instance, the most intense visible lines in the spectrum of lithium occur at 671 nm. (a) What color is light of this wavelength ... 

FIGURE 7.14 Flame Tests (from left to right) for Sodium, Potassium, Lithium, and Barium We can identify elements by the characteristic color of the light they produce when heated. The colors derive from especially bright lines in their emission spectra. 

All the cations of Group I produce a characteristic colour in a flame (lithium, red sodium, yellow potassium, violet rubidium, dark red caesium, blue). The test may be applied quantitatively by atomising an aqueous solution containing Group I cations into a flame and determining the intensities of emission over the visible spectrum with a spectrophotometer Jlame photometry). 

In addition to the emission due to the test element, radiation is also emitted by the flame itself. This background emission, together with turbulence in the flame, results in fluctuations of the signal and prevents the use of very sensitive detectors. The problem may be appreciably reduced by the introduction into the sample of a constant amount of a reference element and the use of a dual-channel flame photometer, which is capable of recording both the test and reference readings simultaneously. The ratio of the intensity of emission of the test element to that of the reference element should be unaffected by flame fluctuations and a calibration line using this ratio for different concentrations of the test element is the basis of the quantitative method. Lithium salts are frequently used as the reference element in the analysis of biological samples. 

The flame coloration and the spectrum (p. 54) afford delicate tests for the presence of lithium. From solutions which are not too dilute it can be precipitated as phosphate, fluoride, or carbonate. Like sodium, it yields an antimonate of slight solubility, but in contradistinction to potassium its platino-chloride and hydrogen tartrate are soluble. 

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. 

There are at least 25 USP or BP formulation monographs that use flame photometry to assay ions of interest (Table This technique is applicable to a variety of situations because of the relatively low cost per sample (in analyst time, instrument capital expense, and testing supplies) reasonable precision (typical relative standard deviation values are 0.6% for sodium, 1% for potassium, and 2% for lithium) low sample volume requirements (as low as 10 pi in some cases) and ease of operation. 

If there is a difference in physical properties between the test solution and the standards it is likely that erroneous results will be obtained. This is quite well recognized and can be readily overcome. Together with variation in flame characteristics between test and standard reading, this is the only type of interference in which a lithium internal standard is really effective. 

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