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How is the strength of an oxyacid measured in water?
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oxyacid
The structure of phosphorous acid, H3PO3.
The strength of an oxyacid is measured by the extent to which it dissociates in water to form hydrogen ions (H⁺).1
You can predict the relative strength of these acids by examining the properties of the central nonmetal atom:
- Electronegativity: Acid strength increases as the electronegativity of the central atom increases. For instance, because chlorine is more electronegative than sulfur, perchloric acid (HClO₄) is a stronger acid than sulfuric acid (H₂SO₄).1
- Oxidation Number: For a specific central atom, acid strength increases as the oxidation number of that atom increases. For example, nitric acid (HNO₃), where nitrogen has an oxidation state of +5, is stronger than nitrous acid (HNO₂), where nitrogen is in a +3 state.1