By the definition of Svante Arrhenius, an acid is a material that can release a proton or hydrogen ion (H+). Hydrogen chloride in water solution ionizes and becomes hydrogen ions and chloride ions.
HCl –> H+ + Cl–
A base, or alkali, is a material that can donate a hydroxide ion (OH–). Sodium hydroxide in water solution becomes sodium ions and hydroxide ions.
NaOH –> Na+ + OH–
By the definition of both Thomas Lowry and J.N. Brønsted working independently in 1923, an acid is a material that donates a proton and a base is a material that can accept a proton. The Arrhenius definition serves well for a limited use. The Lowry- Brønsted definition is broader, including some ideas that might not initially seem to be acid and base types of interaction. Every ion dissociation that involves a hydrogen or hydroxide ion could be considered an acid- base reaction. The G.N. Lewis (1923) idea of acids and bases is broader than the Lowry – Brønsted model. The Lewis definitions are: Acids are electron pair acceptors and bases are electron pair donors.
We encounter acids and bases both in chemistry and in everyday living. They have opposite properties and have the ability to neutralize (cancel) each other. Acids and bases are regulated in the body by the lungs, blood, and kidneys through equilibrium processes.
Properties:
Acids
- taste sour
- react with compounds containing CO32- and form carbon dioxide and water
- turn litmus red
- Acids corrode active metals
- react with zinc, magnesium, or aluminum and form hydrogen (H2(g))
Bases
- taste bitter
- feel soapy or slippery
- turn litmus blue
- they react with most cations to precipitate hydroxides
pH
Scientists use pH scale to measure how acidic or basic a liquid is. The acidic or basic degree of substances is measured in pH units. The scale used spans from 0 to 14. Substances with pH lower than 7 are considered acids, those with pH equal to 7 are considered neutral, and those with pH higher than 7 are considered bases. Substances with low pH (0-4) are very acidic, while those with high pH (10-14) are highly basic.
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