Alkaline earth salts, flame colors

In 1823, Herschel [15] in the Transactions of the Royal Society of Edinburgh published his observations of the colors of flames produced by the introduction of alkaline earth salts. The green color obtained with barium salts is due to BaOH and the reddish color characteristic of strontium salts is caused by SrOH. The red colors of fireworks can also be attributed to emission from SrOH [16]. It was not until the 1950s that modern flame studies [17, 18] identified the molecules that are responsible for the alkaline earth flame colors. In contrast to the alkaline earths, the flame colors of the alkali elements are produced by atomic emission. The formation of molecules such as CaOH and SrOH, in fact, greatly complicates the use of flame absorption and emission for the determination of the concentrations of alkaline earth elements in analytical chemistry. 

The alkaline earth metals can be detected in burning compounds by the colors that they give to flames. Calcium burns orange-red, strontium crimson, and barium yellow-green. Fireworks are often made from their salts (typically nitrates and chlorates, because the anions then provide an additional supply of oxygen) together with magnesium powder. 

When small amounts of alkali metals, alkaline earth metals, or their salts are introduced into a gaseous flame, flame reactions occur relatively easily at low temperatures.The liberated metal atoms are promoted to excited states and then return to their normal states. Radiation corresponding to the characteristic line spectra of the individual metal atoms is emitted as a result of this energy transition. Colored radiation discernible by the human eye, ranging from red to blue, is dependent on the type of metal atoms, as shown in Table 12AP- i... 

State the colors imparted to a Bunsen flame by vaporized salts (chlorides) of the alkali and alkaline earth metals. 

Yellowish-white, slightly lustrous lumps body-centered cubic structure somewhat malleable very easily oxidizable must be kept under petroleum or other oxygen -free liquid to exclude air. d 3.6, mp approx 710 . bp approx 1600. E° (aq) BaJ + /Ba —2.91 V. Description of reactions which are characteristic of alkaline earth metals see Calcium. Solns of sol barium salts give a white ppt with HjS04 or sol sulfates they also color nonluminous flame green. 

CHEMICAL PROPERTIES extremely reactive reacts readily with water, ammonia, halogens, oxygen, and most acids reactions are characteristic of alkaline earth metals soluble salts give a white precipitate with sulfuric acid gives green color in flame very easily oxidi-zable. 

The heavier alkaline earth ions give off characteristic colors when heated in a hot flame. Strontium salts produce the brUliant red color in fireworks, and barium salts produce the green color. 

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