The term alkaline is commonly used as a synonym for for soluble bases. Although the terms, alkali and base (basic), are used interchangeably, their meanings are not the same. All alkaline solutions are basic, yet not all bases are alkaline. A common mistake is referring to the alkalinity of a substance, such as soil, when pH (a base) is the property of measurement.
In chemistry, bases consist of any chemical compound dissolved in water that produces a solution with a hydrogen ion actively lower than that of pure water, such as sodium hydroxide or ammonia. Bases are categorized as the chemical opposite of acids. Bases reduce the hydrogen concentration in water whereas acids increase the concentration. Neutralization occurs when an acid and base combine.
Alkalis, the first base property known to support the Arrhenius definition of a base, are the most common base. In chemistry, the term alkali refers to salts (ionic compounds) containing alkali and alkaline earth metal elements that accept a hydrogen ion (Bronsted-Lowry acid-base theory). Alkaline bases are best known as bases that dissolve in water. Alkali metals react vigorously with water, producing hydroxides and releasing hydrogen. The reaction to air covers the surface with oxides. In nature, ionic compounds (salts) contain alkali metals but never in a pure state. These ionic compounds (salts) react with halogens and form essential components, such as body fluids (electrolytes).
Alkaline bases include a slimy or soapy feel to the touch because of saponification of fatty acids in human skin. Alkalis form hydroxide ions (OH-) when dissolved in water and all are Arrhenius bases. Normally water-soluble, some alkalis, such as barium carbonate, become soluble only when reacting with an acidic solution containing water. Moderately concentrated solutions (pH of 7.1 or greater) turn litmus paper blue and phenolphthalein from colorless to pink. Concentrated solutions cause chemical burns (caustic).
The Bronsten-Lowry Acid-Base Theory
Named for Johannes Bronsted and Thomas Lowry, a Brosted-Lowry base is any substance that accepts a hydrogen icon (proton). A BL acid is any substance that rejects a hydrogen ion, as stated on the New York University website.
Arrhenius Definition of a Base
Arrhenius definition classifies a base as any substance that increases the concentration of hydroxide ions in water (OH-).