Arsenious

Arsenious refers to a chemical state of arsenic where it has an oxidation state of +3. This is in contrast to the arsenate state, where arsenic has an oxidation state of +5. The most common compound exhibiting the arsenious state is arsenic trioxide, often called "white arsenic" or arsenious acid anhydride. Arsenic trioxide itself is a white, crystalline solid. When dissolved in water, it forms arsenious acid, a weak acid.

Compounds containing arsenious ions are generally considered highly toxic. Historically, arsenious compounds have been used as poisons due to their potent toxicity and relatively odorless and tasteless nature, making them difficult to detect. In medicine, very dilute solutions of arsenious acid were historically used in treatments, although this practice is largely obsolete due to the associated risks.

In analytical chemistry, the presence of arsenious compounds can be detected through various chemical tests. The reactivity of arsenious compounds differs from that of arsenates, which is often exploited in these detection methods. Understanding the oxidation state of arsenic is crucial in determining its chemical behavior, environmental fate, and toxicological properties.