Scandium(III) Hydroxide, chemically written as Sc(OH)3, is an inorganic substance. It is an ionic salt composed of a positively charged scandium ion and the negatively charged hydroxide polyatomic ion. Scandium is a metallic element often classified with the rare-earth elements, and Sc(OH)3 is its trivalent hydroxide.
Determining the Name of Sc(OH)3
The naming of Sc(OH)3 follows the systematic rules set by the International Union of Pure and Applied Chemistry (IUPAC) for ionic compounds. The name is constructed by stating the metal name, Scandium, followed by the name of the polyatomic anion, Hydroxide. The hydroxide group (OH) carries a net negative charge of -1.
Since the formula contains three hydroxide ions, the total negative charge is -3. To maintain electrical neutrality, the scandium ion must have a charge of +3 (Sc\(^{3+}\)). The Roman numeral (III) is included in the name, Scandium(III) Hydroxide, to explicitly indicate this +3 oxidation state. Although scandium typically only exhibits the +3 state, IUPAC nomenclature requires the use of Roman numerals for d-block metals to ensure clarity regarding the metal’s valence.
Key Physical and Chemical Properties
Scandium(III) Hydroxide is a white solid, often appearing as a gelatinous or amorphous precipitate when formed in an aqueous solution. The anhydrous compound has a molecular weight of approximately 95.98 grams per mole. It is only slightly soluble in pure water, confirmed by its very small solubility product (\(K_{sp}\)) value of about \(2.22 \times 10^{-31}\).
Amphoteric Nature
A defining characteristic of Scandium(III) Hydroxide is its amphoteric nature, meaning it can react with both acids and strong bases. It readily dissolves in acids to form the corresponding scandium salt, such as scandium chloride or nitrate. It shows chemical behavior similar to hydroxides near the aluminum group, reacting to form complex ions in the presence of strong alkali.
Hydration and Stability
The formula Sc(OH)3 represents the pure, anhydrous compound. However, it is often encountered as a hydrate (Sc(OH)3 \(\cdot\) xH2O) or as an oxide-hydroxide form (ScO(OH)). The formation of the oxide-hydroxide structure significantly lowers the already limited solubility, demonstrating the compound’s sensitivity to its surrounding environment and age.
Role in Scandium Chemistry and Technology
Scandium(III) Hydroxide is an important intermediate in refining and purifying scandium from its raw source materials. Precipitation of scandium as its hydroxide is an effective method for separating it from other rare-earth elements and impurities during mineral processing. This separation technique is valuable because scandium is often found alongside these elements in minerals like euxenite and gadolinite.
Once purified, the hydroxide is typically heated to yield high-purity scandium oxide (Sc2O3), which is the most common commercial form of the element. Scandium compounds derived from this oxide are applied in high-tech industries. These applications include the manufacture of aerospace alloys, where scandium significantly strengthens aluminum. Scandium oxide is also used as a dopant in the electrolyte material of solid oxide fuel cells (SOFCs) to improve performance and stability.