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How does sulfuric acid ionize in water?

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The structure of phosphorous acid, H3PO3. — oxyacid The structure of phosphorous acid, H₃PO₃.

Sulfuric acid ( $H_{2} S O_{4}$ ) is a diprotic acid, meaning it can donate two hydrogen ions per molecule in a sequential process when it ionizes in water.1

The ionization occurs in two distinct steps:

First Ionization: The acid releases its first hydrogen ion completely to form the hydronium ion ( $H_{3} O^{+}$ ) and the hydrogen sulfate ion ( $H S O_{4}^{-}$ ).1
Second Ionization: The hydrogen sulfate ion only partially dissociates, releasing a second hydrogen ion to form additional hydronium ions and the sulfate ion ( $S O_{4}^{2 -}$ ).1

Because the first ion is given up completely, sulfuric acid is considered a strong mineral acid that ionizes fully in water to produce hydronium and hydrogen sulfate ions, with further dissociation occurring in dilute solutions.1