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Why is sulfuric acid considered a diprotic acid?

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A labeled diagram highlights sulfur's position on the periodic table, showing its atomic number 16, symbol S, atomic weight range, electron configuration, and classification as a solid, strongly acidic, orthorhombic nonmetal at room temperature. — sulfur Chemical properties of sulfur.

Sulfuric acid ( $H_{2} S O_{4}$ ) is classified as a diprotic acid because each molecule is capable of donating two hydrogen ions during the process of dissociation in water.12

This release occurs in two sequential steps:
* First step: The molecule gives up its first hydrogen ion completely to form the hydrogen sulfate ion ( $H S O_{4}^{-}$ ).2
* Second step: The remaining hydrogen sulfate ion partially dissociates, releasing a second hydrogen ion to produce the sulfate ion ( $S O_{4}^{2 -}$ ).2

Because the molecule contains two ionizable hydrogen atoms that can be donated in sequence, it is defined as diprotic.12