Lithium hydroxide (LiOH) is an inorganic compound that exists as a white, crystalline solid, typically in anhydrous or monohydrate form. It is classified as a strong base, meaning it readily releases hydroxide ions (\(\text{OH}^{-}\)) when placed in a solvent. Understanding its solubility—the ability of the substance to dissolve in a liquid—is a foundational concept that governs its practical uses.
The Solubility of Lithium Hydroxide
Lithium hydroxide is highly soluble in water, a characteristic fundamental to its chemical behavior and industrial applications. When dissolved, this ionic compound dissociates completely, breaking apart into its constituent ions: one positively charged lithium ion (\(\text{Li}^{+}\)) and one negatively charged hydroxide ion (\(\text{OH}^{-}\)). This complete separation classifies \(\text{LiOH}\) as a strong electrolyte, meaning its solution is an excellent conductor of electricity.
The solubility of \(\text{LiOH}\) is approximately 12.8 grams dissolving in 100 milliliters of water at 20 degrees Celsius. This high solubility is due to the strong attractive forces between the water molecules and the individual ions, which are powerful enough to overcome the internal forces holding the crystal structure together. Furthermore, the solubility of lithium hydroxide increases as the temperature of the water rises, a common pattern for many solid compounds.
Understanding the General Rules of Solubility
The solubility of lithium hydroxide can be predicted by the general rules that govern how ionic compounds dissolve in water. One primary principle is that of “like dissolves like,” where polar solvents, such as water, are effective at dissolving polar or ionic solutes. Since water molecules possess both slightly positive and slightly negative poles, they can surround and pull apart the charged ions in the \(\text{LiOH}\) crystal lattice.
A more specific chemical guideline concerns the behavior of alkali metals, which are the elements found in Group 1 of the periodic table, including lithium. A major solubility rule states that all compounds containing an alkali metal ion (\(\text{Li}^{+}\), \(\text{Na}^{+}\), \(\text{K}^{+}\), etc.) are soluble in water without exception. Lithium hydroxide’s solubility is therefore a direct confirmation of this rule.
Lithium hydroxide is an exception to the general guideline concerning hydroxides. Most compounds containing the hydroxide ion (\(\text{OH}^{-}\)) are considered insoluble in water, such as magnesium hydroxide or iron hydroxide. However, the hydroxides of the alkali metals, including lithium hydroxide, are exceptions and are readily soluble. The strong force of attraction between the small lithium ion and the water molecules plays a significant role in overriding the tendency for hydroxides to be insoluble.
Essential Applications of Lithium Hydroxide
The chemical properties of \(\text{LiOH}\), particularly its strong basicity and high solubility, make it useful in several industrial and specialized applications. One recognized use is in carbon dioxide (\(\text{CO}_2\)) scrubbing systems, which are deployed in confined environments like spacecraft, submarines, and rebreathers. In this process, solid lithium hydroxide reacts with exhaled carbon dioxide to form solid lithium carbonate and water, effectively purifying the air.
Another major application is its use in the battery industry, where it is a precursor material for the cathode in lithium-ion batteries. The purity of \(\text{LiOH}\) is important for manufacturing the high-performance cathode materials required for electric vehicles and portable electronics. The compound is also used to produce certain lubricating greases, such as lithium stearate, by reacting with fatty acids in a process called saponification.
The resulting lithium-based greases are effective across a wide range of temperatures and pressures, making them popular in the automotive and industrial machinery sectors. Furthermore, lithium hydroxide is used in general chemical synthesis as a strong base for controlling the acidity of solutions in various manufacturing processes.