Arsenic

Arsenic: the essentials

 Brief description: elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semimetallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidises to arsenous oxide which has a garlic odour.

Arsenic and its compounds are poisonous as any reader of "who-done-it" books knows. Upon heating arsenic and some minerals containing arsenic, it sublimes (transfers from the solid to the gaseous state, without passing through the liquid state).

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Isolation

Isolation: it is not usually necessary to make arsenic in the laboratory as it is commercially available. Arsenic is found in nature in a number of minerals including realgar (As₄S₄), orpiment (As₂S₃), arsenolite (As₂O₃), and iron minerals such as arsenopyrite (FeAsS) and loellingite (FeAs₂). Arsenic is made on an industrial scale by heating appropriate minerals in the absence of air. The arsenic is condensed out as a solid.

FeAsS (700°C) → FeS + As(g) → As(s)

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