Calcium oxide [1305-78-8].
» Lime, when freshly ignited to constant weight, contains not less than 95.0 percent of CaO.
Packaging and storage Preserve in tight containers.
A: Moisten it with water: heat is generated, and a white powder is obtained (calcium hydroxide or slaked lime). Mix the powder with 3 or 4 times its weight of water: a smooth magma of lime forms that is alkaline to litmus.
B: Slake 1 g with 20 mL of water, and add 6 N acetic acid until the lime is dissolved: the resulting solution responds to the test for Calcium 191.
Loss on ignition 733 Ignite a portion to constant weight in a tared platinum crucible at 1100 ± 50: it loses not more than 10.0% of its weight.
Insoluble substances Slake 5.0 g, then mix with 100 mL of water, followed by hydrochloric acid, dropwise, with agitation, until solution takes place: the resulting solution after boiling and cooling is acid, and when filtered through a tared crucible, washed with water until free of chlorides, and dried at 105 for 1 hour yields not more than 50 mg of insoluble substances (1.0%).
Carbonate Slake 1 g, mix with 50 mL of water, and decant the greater portion of the milky liquid: the addition of an excess of 3 N hydrochloric acid to the residue does not cause more than a slight effervescence.
Magnesium and alkali salts Dissolve 500 mg in 30 mL of water and 15 mL of 3 N hydrochloric acid. Neutralize the solution with 6 N ammonium hydroxide, heat to boiling, and add ammonium oxalate TS to precipitate the calcium completely. Heat the mixture on a steam bath for 1 hour, cool, dilute with water to 100 mL, mix, and filter. To 50 mL of the filtrate add 0.5 mL of sulfuric acid, evaporate to dryness, and ignite in a tared platinum crucible to constant weight. The weight of the residue does not exceed 9 mg.
Assay Ignite about 1 g of Lime in a muffle furnace to constant weight, cool, weigh accurately, and dissolve in 20 mL of 3 N hydrochloric acid. Cool the solution, transfer to a 500-mL volumetric flask with the aid of water, dilute with water to volume, and mix. Transfer 50.0 mL to a suitable container, add 100 mL of water, 15 mL of 1 N sodium hydroxide, and 300 mg of hydroxy naphthol blue, and titrate with 0.05 M edetate disodium VS until the solution is deep blue in color. Each mL of 0.05 M edetate disodium is equivalent to 2.804 mg of CaO.