Through examples uncovered in the part on acids and bases proton-transfer processes are damaged into two theoretical steps: (1) donation that a proton by an acid, and (2) acceptance of a proton through a base. (Water offered as the base in the acid example and also as the mountain in the base instance ). The hypothetical steps room useful because they make it straightforward to view what varieties is left ~ an mountain donated a proton and what species is developed when a base embraced a proton. Us shall use hypothetical steps or half-equations in this section, but you should bear in mind that complimentary protons never ever 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 other species, we can write the half-equation:

< extNH_4^+ ightarrow extH^+ + extNH_3>

The submicroscopic representations below show the donation of the proton of ammonium. The remove of this proton results in NH3, which is quickly seen at the submicroscopic level.

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But NH3 is just one of the compound we know as a weak base. In other words, as soon as it donates a proton, the weak acid NH4+ is transformed right into a weak basic NH3. An additional example, this time beginning with a weak base, is listed by fluoride ion:

< extF^- + extH^+ ightarrow extHF>

The submicroscopic representation over shows exactly how the addition of a proton to fluoride counter a weak base (F- in green) into a weak acid (HF).

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The instance just defined for NH4+ and also NH3 or for F– and HF applies to every acids and bases. Whenever an acid donates a proton, the acid changes into a base, and whenever a basic accepts a proton, an acid is formed. One acid and a base which differ just by the visibility or lack of a proton are referred to as a conjugate acid-base pair. For this reason NH3 is called the conjugate base of NH4+, and also NH4+ is the conjugate acid 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 permits us to do a very simple statement around relative strengths of acids and bases. The more powerful an acid, the weaker that conjugate base, and, whereas the more powerful a base, the weaker that conjugate acid.

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

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altconjugate base of a weak acid is a strong base