alcali

Alkali, usually spelled alkali in English, refers to a subset of bases that dissolve in water to produce alkaline solutions. In modern chemistry, alkalis include the hydroxides of the alkali metals (such as lithium, sodium, and potassium hydroxides) and soluble carbonates and bicarbonates (such as sodium carbonate and potassium carbonate) that raise the pH of water.

A key distinction is that all alkalis are bases, but not all bases are alkalis. The defining feature of an alkali is solubility in water and the ability to form basic, or alkaline, solutions. Some bases, such as oxide or hydroxide solids with low solubility, may act as bases but are not classified as alkalis in common usage.

Common examples of alkalis include sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium carbonate (Na2CO3). These substances react with acids in neutralization reactions to form salts and water. Alkalis are typically caustic and can be corrosive, requiring careful handling and appropriate safety measures.

Applications of alkalis are wide-ranging. They are used in soap making through saponification, in paper production, in water treatment and soil conditioning, and as cleaning agents. Sodium bicarbonate (baking soda) and related carbonates are also alkalis and find use in cooking and baking as well as in certain deacidification processes.

Etymology and history: the word alkali traces to the Arabic al-qālī, meaning ashes of the plant, from which plant ashes yielded potash and related alkaline materials. The term entered European languages in the medieval period and has since evolved to describe water-soluble bases that impart alkaline character to solutions.