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Microcrystal Test for Sodium and Potassium

Sodium and Potassium Uranyl Acetate

The presence of sodium is indicated by the tetrahedron crystals and the presence of potassium is indicated by the lath crystals.

Transmitted Oblique Illumination


A standard microcrystal test for the presence of sodium and/or potassium ions in solution is to add a drop of uranyl acetate to the dried salt. The uranyl acetate solution should be made a little acidic with acetic acid. If sodium ions are present well in excess of any divalent ions (calcium, magnesium, etc.) then the tetrahedrons of sodium uranyl acetate form. If potassium is present then lathe crystals of potassium uranyl acetate form. If both are present then the sodium uranyl acetate forms first followed by the potassium uranyl acetate because the potassium uranyl acetate is more soluble and stays in solution longer than the sodium uranyl acetate.

Significance in the Environment:

Characteristic Features:

Associated Particles:


Chamot, Emile Monnin and Clyde Walter Mason, HANDBOOK OF CHEMICAL MICROSCOPY, Volume II, pp. 51-8, 1940.