Through examples found in the sections on acids and bases proton-transfer procedures are damaged into two theoretical steps: (1) donation the a proton by one acid, and also (2) acceptance of a proton by a base. (Water offered as the basic in the mountain example and also as the mountain in the base instance ). The hypothetical steps are useful since they make it basic to check out what varieties is left after ~ an mountain donated a proton and also what varieties is developed when a base accepted a proton. Us shall use hypothetical steps or half-equations in this section, however you should bear in mental that cost-free protons never actually exist in aqueous solution.

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Suppose we very first consider a weak acid, the ammonium ion. When it donates a proton to any type of other species, we deserve to write the half-equation:

\< \textNH_4^+ \rightarrow \textH^+ +\textNH_3\>

The submicroscopic representations below show the donation that the proton of ammonium. The remove of this proton results in NH3, i m sorry is easily seen at the submicroscopic level.

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But NH3 is among the link we understand as a weak base. In other words, as soon as it donates a proton, the weak acid NH4+ is transformed into a weak basic NH3. One more example, this time beginning with a weak base, is provided by fluoride ion:

\<\textF^- + \textH^+ \rightarrow \textHF\>

The submicroscopic representation above shows how the addition of a proton to fluoride switch a weak basic (F- in green) into a weak acid (HF).

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The instance just explained for NH4+ and also NH3 or because that F– and also HF applies to every acids and also bases. Whenever an mountain donates a proton, the acid changes into a base, and whenever a basic accepts a proton, an acid is formed. One acid and also a base which differ just by the visibility or absence of a proton are referred to as a conjugate acid-base pair. Therefore NH3 is referred to as the conjugate base of NH4+, and also NH4+ is the conjugate mountain of NH3. Similarly, HF is the conjugate mountain of F–, and also F– the conjugate base of HF.


The usage of conjugate acid-base pairs allows us to make a very basic statement around relative staminas of acids and bases. The stronger an acid, the weaker that conjugate base, and, whereas the stronger a base, the weaker its conjugate acid.

TABLE \(\PageIndex1\):Important Conjugate Acid-Base Pairs.

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