Base (chemistry)

Article

August 13, 2022

A base or lye – also called an alkali – is a substance that has properties opposite to an acid. The degree to which a substance dissolved in water is basic is indicated by the pH value: 7 is neutral, higher values ​​are basic, values ​​lower than 7 are acidic.

Measurement

Litmus paper is traditionally used to test whether a substance is alkaline: a base in solution will turn the paper blue. A more modern and accurate way is with a pH meter.

Definitions

Bases can be defined in three ways: according to Arrhenius according to Brønsted and Lowry according to Lewis

According to Arrhenius

An Arrhenius base (an Arrhenius base) is a molecule that gives rise to the formation of a hydroxide ion (OH−) in water (H2O). The molecule may also contain a hydroxide ion itself, but it does not have to. Two examples of Arrhenius bases are sodium hydroxide (NaOH) and ammonia (NH3): NaOH After + + OH {\displaystyle {\ce {NaOH -> Na^+ + OH^-}}} NH 3 + huh 2 O NH 4 + + OH {\displaystyle {\ce {NH3 + H2O -> NH4^+ + OH^-}}}

According to Brønsted and Lowry

A base according to Johannes Nicolaus Brønsted and Thomas Lowry is a molecule or negatively charged ion that can accept hydrogen ions (H+) and is called a brønsted base. These two chemists came up with this definition simultaneously, but independently, in 1923. However, often only the name of Brønsted is mentioned. Every Arrhenius base is also a Brønsted base, but not vice versa. According to Arrhenius, the molecule must be dissolved in water. However, according to the definition of Brønsted and Lowry, this is not necessary.

According to Lewis

A Lewis base is a molecule with a lone pair of electrons (:) and is called a Lewis base. The electron pair can be shared with an acid, for example in the reaction between boron trifluoride and ammonia: BF 3 ( pickles ) + : NH 3 ( base ) f 3 B : NH 3 {\displaystyle {\ce {BF3 (acid) + :NH3 (base) -> F3B:NH3}}} All brønsted bases are also Lewis bases, but the reverse is not always true.

Examples of bases

sodium hydroxide (NaOH) (a solution of sodium hydroxide in water is called caustic soda) potassium hydroxide (KOH) (a solution of potassium hydroxide in water is called caustic potash) barium hydroxide (Ba(OH)2) (a solution of barium hydroxide in water is called barite water) calcium hydroxide (Ca(OH)2) (a solution of calcium hydroxide in water is called lime water) ammonia (NH3) sodium carbonate Na2CO3 urea