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Proton donation is a fundamental concept in chemistry, especially in acid-base reactions. To understand proton donation, recall the definition of an acid according to the Brønsted-Lowry theory: an acid is a substance that donates a proton (which is essentially a hydrogen ion, \( \mathrm{H}^+ \)). This process can be seen in various chemical reactions where a compound releases a proton into the surrounding environment.

In the given exercise, \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) acts as an acid by donating a proton. This donation turns \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) into \( \mathrm{HPO}_{3}^{2-} \), illustrating its acidic properties. The chemical equation showing this is:

• \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{HPO}_{3}^{2-} + \mathrm{H}_{3} \mathrm{O}^{+} \)

Here, \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) transfers a \( \mathrm{H}^+ \) to water, creating \( \mathrm{HPO}_{3}^{2-} \) and hydronium ion \( \mathrm{H}_{3} \mathrm{O}^{+} \). Proton donation is key to understanding how acids behave and interact with other substances.

Proton acceptance occurs when a substance behaves as a base. A base, as defined by the Brønsted-Lowry theory, is a compound that accepts a proton from another substance. When accepting a proton, the base typically forms a new compound.

In the provided exercise, \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) is capable of acting as a base by accepting a proton to become \( \mathrm{H}_{3} \mathrm{PO}_{3} \). The corresponding chemical equation for this transformation is:

• \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} + \mathrm{H}^{+} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3} \)

This equation demonstrates \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) gaining a \( \mathrm{H}^+ \) and turning into its conjugate acid form \( \mathrm{H}_{3} \mathrm{PO}_{3} \). Understanding proton acceptance helps in recognizing how bases behave in chemical reactions and interact with acids.

Chemical equations are symbolic representations of chemical reactions. They provide insight into how substances interact and change during a reaction. A chemical equation must balance in terms of atoms and charge, obeying the law of conservation of mass.

In acid-base reactions, chemical equations illustrate how protons are transferred between substances. For instance, in the example where \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) acts as an acid, the chemical equation is:

• \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{HPO}_{3}^{2-} + \mathrm{H}_{3} \mathrm{O}^{+} \)

This equation shows the proton donation process, with reactants and products clearly outlined.

Conversely, when \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} \) acts as a base, the following chemical equation describes the reaction:

• \( \mathrm{H}_{2} \mathrm{PO}_{3}^{-} + \mathrm{H}^{+} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3} \)

This balance in the chemical equation ensures that the transactions of protons and formation of compounds are accurately represented. Grasping how to read and write chemical equations is crucial for anyone studying chemistry, as it is the language of chemical reactions.