Through examples uncovered in the sections on acids and also bases proton-transfer processes are broken into two theoretical steps: (1) donation of a proton by an acid, and (2) accept of a proton through a base. (Water offered as the base in the mountain example and as the acid in the base instance ). The hypothetical steps space useful because they do it simple to check out what species is left ~ an mountain donated a proton and also what varieties is formed when a base welcomed a proton. We shall use hypothetical steps or half-equations in this section, yet you should bear in mental that free protons never ever actually exist in aqueous solution.

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Suppose we an initial consider a weak acid, the ammonium ion. As soon as it donates a proton to any type of other species, we have the right to write the half-equation:

< extNH_4^+ ightarrow extH^+ + extNH_3>

The submicroscopic representations listed below show the donation the the proton that ammonium. The removal of this proton outcomes in NH3, which is quickly seen at the submicroscopic level.

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But NH3 is one of the compounds we understand as a weak base. In various other words, as soon as it donates a proton, the weak acid NH4+ is transformed right into a weak basic NH3. Another example, this time beginning with a weak base, is provided by fluoride ion:

< extF^- + extH^+ ightarrow extHF>

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

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The case just explained for NH4+ and NH3 or for F– and also HF uses to every acids and bases. Whenever an acid donates a proton, the acid transforms into a base, and also whenever a basic accepts a proton, an mountain is formed. An acid and also a basic which differ only by the visibility or lack of a proton are called a conjugate acid-base pair. Therefore NH3 is referred to as the conjugate basic of NH4+, and also NH4+ is the conjugate acid of NH3. Similarly, HF is the conjugate mountain of F–, and F– the conjugate base of HF.


The use of conjugate acid-base pairs permits us to make a very an easy statement around relative strengths of acids and also bases. The stronger an acid, the weaker that is conjugate base, and, vice versa, the more powerful a base, the weaker that conjugate acid.

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

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altwhich pair is not a conjugate acid-base pair?