1.7 Polyprotic Acids
- Page ID
- 32057
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We have seen examples of acids that contain more than one hydrogen ion that can be lost. Sulfuric acid, H2SO4, for example, has two hydrogen ions that it can give up. The first hydrogen ion is released as:
\[H_2SO_{4 (aq)} \rightarrow H^+_{(aq)} + HSO^-_{4(aq)}\]
The second hydrogen will be more difficult to remove because it must now be removed from a negative ion, HSO4-.
\[HSO^-_{4(aq)} \rightarrow H^+_{(aq)} + SO^{2-}_{4(aq)}\]
For acids that can donate more than one hydrogen, it will always be easier to donate the first \(\ce{H+}\) than the second. If there are more hydrogens to release, each \(\ce{H+}\) is more difficult to remove because of the increasingly positive charge of the rest of the molecule.
Note
Acids that can donate more than one hydrogen ion are called polyprotic
How many \(\ce{H+}\) can citric acid, \(\ce{H3C6H5O7}\), release?
Citric acid can release three \(\ce{H+}\). The reactions would be:
1. \(\ce{H3C6H5O7(aq) -> H^{+}(aq) + H2C6H5O7^{-}(aq)}\)
2. \(\ce{H2C6H5O7^{-}(aq) -> H^{+}(aq) + HC6H5O7^{2-}(aq)}\)
3. \(\ce{HC6H5O7^{2-}(aq) -> H^{+}(aq) + C6H5O7^{3-}(aq)}\)