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1.6 Amphoteric Substances

  • Page ID
    32056
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    Were you surprised in the last section to see water being described as an acid? In the ammonia reaction, water acted as an acid because it donated a proton (hydrogen ion) to ammonia:

    \(\ce{NH3(g) + H2O(l) <=> NH4^{+}(aq) + OH^{-}(aq)}\)

    Compare this to another reaction we looked at earlier when we saw how hydrochloric acid acted as an acid by donating a proton to water:

    \(\ce{HCl(g) + H2O(l) <=> H3O^{+}(aq) + Cl^{-}(aq)}\)

    In this reaction, water is acting as a base because it accepts a proton from \(\ce{HCl(g)}\) .

    Substances that can act as
    an acid is one reaction and
    as a base in another are called
    amphoteric substances

    Just to confuse you, the term
    amphiprotic means the same thing

    Here is another example of an amphoteric substance. In the first reaction the bisulfate ion, \(\ce{HSO4-}\) acts as a base. In the second reaction it acts as an acid:

    1.
    \(\ce{HSO4^{-} + H3O^{+} <=> H2SO4 + H2O}\)
    \(\ce{HSO4-}\) accepts a proton from \(\ce{H3O+}\)
    2.
    \(\ce{HSO4^{-} + OH^{-} <=> H2O + SO4^{2-}}\)
    \(\ce{HSO4-}\) gives (donates) a proton to \(\ce{OH-}\)

    1.6 Amphoteric Substances is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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