álcalis

Álcalis, in chemistry, are bases that dissolve in water to form alkaline solutions. The term traditionally follows the Arrhenius definition: substances that increase the concentration of hydroxide ions (OH-) in aqueous solution. Because they produce an alkaline pH, they are often described as alkaline bases. The name derives from the Arabic al-qali, meaning ashes, reflecting historical production from ash-derived hydroxides.

Most common álcalis are the hydroxides of alkali metals, such as lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH). Alkaline earth metal hydroxides, notably calcium hydroxide (Ca(OH)2), strontium hydroxide (Sr(OH)2), and barium hydroxide (Ba(OH)2), are also alkalis but differ in solubility. In practice, alkalis are typically soluble bases, readily releasing OH- ions in water. They are usually caustic and can be highly reactive with acids and with carbon dioxide in air.

Reactions involving álcalis include neutralization with acids to form salts and water. They are essential in many industrial and environmental processes: the chloralkali process yields sodium hydroxide; NaOH and KOH are used in soap and detergent manufacture, paper production, water treatment, and pH control; Ca(OH)2 is employed in construction (lime) and agriculture to adjust soil pH.

Safety and handling emphasize their caustic, corrosive nature; contact with skin or eyes can cause severe burns. Proper storage in compatible containers and the use of protective equipment are standard precautions.