Through examples uncovered in the part on acids and also bases proton-transfer processes are damaged into two theoretical steps: (1) donation of a proton by one acid, and (2) acceptance of a proton through a base. (Water offered as the base in the mountain example and as the acid in the base example ). The hypothetical steps room useful due to the fact that they do it simple to see what types is left ~ an mountain donated a proton and also what types is formed when a base accepted a proton. We shall use hypothetical steps or half-equations in this section, yet you should bear in psychic that cost-free protons never actually exist in aqueous solution.

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Suppose we first consider a weak acid, the ammonium ion. Once it donates a proton to any kind of other species, we can write the half-equation:

< extNH_4^+ ightarrow extH^+ + extNH_3>

The submicroscopic representations below show the donation of the proton the ammonium. The removal of this proton outcomes in NH3, i m sorry is easily seen in ~ the submicroscopic level.

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But NH3 is just one of the link we understand as a weak base. In various other words, once it donates a proton, the weak mountain NH4+ is transformed into a weak basic NH3. One more example, this time starting with a weak base, is noted by fluoride ion:

< extF^- + extH^+ ightarrow extHF>

The submicroscopic representation above shows just how the enhancement of a proton come fluoride counter a weak base (F- in green) into a weak acid (HF).

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The case just described for NH4+ and NH3 or because that F– and HF uses to every acids and also bases. At any time an acid donates a proton, the acid changes into a base, and also whenever a basic accepts a proton, an mountain is formed. One acid and also a base which differ only by the presence or absence of a proton are referred to as a conjugate acid-base pair. Thus NH3 is dubbed the conjugate basic of NH4+, and NH4+ is the conjugate acid of NH3. Similarly, HF is the conjugate acid of F–, and F– the conjugate base of HF.


The usage of conjugate acid-base pairs enables us to do a very simple statement around relative staminas of acids and also bases. The stronger an acid, the weaker the conjugate base, and, conversely, the more powerful a base, the weaker that conjugate acid.

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

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altwhich is an acid-conjugate base pair?