“acid”的概念、定义、翻译、参考文献-科学参考

acid

Chemistry

1. A type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction, for an acid HX, is commonly written:
$HX ⇌ H^{+} {+ X}^{-}$
In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:
${HX + H}_{2} O ⇌ H_{3} O^{+} {+ X}^{-}$
The ion H₃O⁺ is the oxonium ion (or hydroxonium ion or hydronium ion). This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and give colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. ethanoic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant. See also base.
2. In the Lowry–Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). For example, in
${HCN + H}_{2} O ⇌ H_{3} O^{+} {+ CN}^{-}$
the HCN is an acid, in that it donates a proton to H₂O. The H₂O is acting as a base in accepting a proton. Similarly, in the reverse reaction H₃O⁺ is an acid and CN⁻ a base. In such reactions, two species related by loss or gain of a proton are said to be conjugate. Thus, in the reaction above HCN is the conjugate acid of the base CN⁻, and CN⁻ is the conjugate base of the acid HCN. Similarly, H₃O⁺ is the conjugate acid of the base H₂O. An equilibrium, such as that above, is a competition for protons between an acid and its conjugate base. A strong acid has a weak conjugate base, and vice versa. Under this definition water can act as both acid and base. Thus in
${NH}_{3} {+ H}_{2} O ⇌ {NH}_{4}^{+} {+ OH}^{-}$
the H₂O is the conjugate acid of OH⁻. The definition also extends the idea of acid–base reaction to solvents other than water. For instance, liquid ammonia, like water, has a high dielectric constant and is a good ionizing solvent. Equilibria of the type
${NH}_{3} {+ Na}^{+} {Cl}^{-} ⇌ {Na}^{+} {NH}_{2}^{-} + HCl$
can be studied, in which NH₃ and HCl are acids and NH₂⁻ and Cl⁻ are their conjugate bases.
3. A further extension of the idea of acids and bases was made in the Lewis theory (Gilbert Newton Lewis, 1923). In this, a Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses ‘traditional’ acid–base reactions. In
$HCl + NaOH \to {NaCl + H}_{2} O$
the reaction is essentially
$H^{+} {+ : OH}^{-} \to H : OH$
i.e. donation of an electron pair by OH⁻. But it also includes reactions that do not involve ions, e.g.
$H_{3} {N : + BCl}_{3} \to H_{3} {NBCl}_{3}$
in which NH₃ is the base (donor) and BCl₃ the acid (acceptor). The Lewis theory establishes a relationship between acid–base reactions and oxidation–reduction reactions. See also HSAB principle.

See also aqua acid; hydroxoacid; oxoacid.

Chemical Engineering

A chemical compound or material containing hydrogen that has the tendency to lose protons and form hydrogen ions in solution. Solutions of acids have pH values less than 7.

Biology

A type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction, for an acid HX, is commonly written:
$HX ⇌ H^{+} + X^{-}$
In fact, the hydrogen ion (the proton) is hydrated, and the complete reaction is:
$HX + H_{2} O ⇌ H_{3} O^{+} + X^{-}$
The ion H₃O⁺ is the hydroxonium ion. The strength of an acid depends on the extent to which it dissociates: strong acids (e.g. sulphuric acid and hydrochloric acid) are almost completely dissociated in water; weak acids (e.g. carbonic acid) are only partially dissociated. See also buffer; ph scale. Compare base.

Geology and Earth Sciences

According to the Brønsted–Lowry theory, a substance that in solution liberates hydrogen ions or protons. The Lewis theory states that an acid is a substance that acts as an electron-pair acceptor. An acid reacts with a base to give a salt and water (neutralization), and has a pH of less than 7.0. The theory was proposed in 1923 by the Danish physical chemist Johannes Nicolaus Brønsted (1879–1947) and the British chemist Thomas Martin Lowry (1874–1936), and independently by the American theoretical chemist Gilbert Newton Lewis (1875–1946).

单词	acid
释义	acid Chemistry 1. A type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction, for an acid HX, is commonly written: $HX ⇌ H^{+} {+ X}^{-}$ In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is: ${HX + H}_{2} O ⇌ H_{3} O^{+} {+ X}^{-}$ The ion H₃O⁺ is the oxonium ion (or hydroxonium ion or hydronium ion). This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and give colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. ethanoic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant. See also base. 2. In the Lowry–Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). For example, in ${HCN + H}_{2} O ⇌ H_{3} O^{+} {+ CN}^{-}$ the HCN is an acid, in that it donates a proton to H₂O. The H₂O is acting as a base in accepting a proton. Similarly, in the reverse reaction H₃O⁺ is an acid and CN⁻ a base. In such reactions, two species related by loss or gain of a proton are said to be conjugate. Thus, in the reaction above HCN is the conjugate acid of the base CN⁻, and CN⁻ is the conjugate base of the acid HCN. Similarly, H₃O⁺ is the conjugate acid of the base H₂O. An equilibrium, such as that above, is a competition for protons between an acid and its conjugate base. A strong acid has a weak conjugate base, and vice versa. Under this definition water can act as both acid and base. Thus in ${NH}_{3} {+ H}_{2} O ⇌ {NH}_{4}^{+} {+ OH}^{-}$ the H₂O is the conjugate acid of OH⁻. The definition also extends the idea of acid–base reaction to solvents other than water. For instance, liquid ammonia, like water, has a high dielectric constant and is a good ionizing solvent. Equilibria of the type ${NH}_{3} {+ Na}^{+} {Cl}^{-} ⇌ {Na}^{+} {NH}_{2}^{-} + HCl$ can be studied, in which NH₃ and HCl are acids and NH₂⁻ and Cl⁻ are their conjugate bases. 3. A further extension of the idea of acids and bases was made in the Lewis theory (Gilbert Newton Lewis, 1923). In this, a Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses ‘traditional’ acid–base reactions. In $HCl + NaOH \to {NaCl + H}_{2} O$ the reaction is essentially $H^{+} {+ : OH}^{-} \to H : OH$ i.e. donation of an electron pair by OH⁻. But it also includes reactions that do not involve ions, e.g. $H_{3} {N : + BCl}_{3} \to H_{3} {NBCl}_{3}$ in which NH₃ is the base (donor) and BCl₃ the acid (acceptor). The Lewis theory establishes a relationship between acid–base reactions and oxidation–reduction reactions. See also HSAB principle. See also aqua acid; hydroxoacid; oxoacid. Chemical Engineering A chemical compound or material containing hydrogen that has the tendency to lose protons and form hydrogen ions in solution. Solutions of acids have pH values less than 7. Biology A type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction, for an acid HX, is commonly written: $HX ⇌ H^{+} + X^{-}$ In fact, the hydrogen ion (the proton) is hydrated, and the complete reaction is: $HX + H_{2} O ⇌ H_{3} O^{+} + X^{-}$ The ion H₃O⁺ is the hydroxonium ion. The strength of an acid depends on the extent to which it dissociates: strong acids (e.g. sulphuric acid and hydrochloric acid) are almost completely dissociated in water; weak acids (e.g. carbonic acid) are only partially dissociated. See also buffer; ph scale. Compare base. Geology and Earth Sciences According to the Brønsted–Lowry theory, a substance that in solution liberates hydrogen ions or protons. The Lewis theory states that an acid is a substance that acts as an electron-pair acceptor. An acid reacts with a base to give a salt and water (neutralization), and has a pH of less than 7.0. The theory was proposed in 1923 by the Danish physical chemist Johannes Nicolaus Brønsted (1879–1947) and the British chemist Thomas Martin Lowry (1874–1936), and independently by the American theoretical chemist Gilbert Newton Lewis (1875–1946).
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