Final answer:
The hydrogen placement in chemical formulas depends on its association within polyatomic ions and charge balance. Hypochlorous acid is correctly written as HClO because the subscript number corresponds to the number of oxygen atoms, not the charge.
Step-by-step explanation:
In chemical nomenclature, numerical prefixes and parentheses are used to indicate the composition of ionic compounds, especially when dealing with polyatomic ions. For example, in aluminum monohydrogen phosphate (Al2(HPO4)3), the (HPO4)³− ion is a polyatomic ion that is present with three ions to balance the charge of two Al³⁺ ions.
The hydrogen stays within the parentheses because it is part of the polyatomic ion. In contrast, for the copper(I) dihydrogen phosphate (CuH2PO4), the dihydrogen phosphate ion (H2PO4)− is matched with one Cu⁺ ion, and the hydrogen atoms are adjacent to the metal cation, indicating they are not part of the charge-balancing.
When writing formulas for acids such as hypochlorous acid (HClO), charges are not explicitly mentioned in the formula. Instead, the formula reflects the composition of the acid without directly showing the charge balance.
The subscript indicates the number of oxygen atoms, and since hypochlorous acid contains only one oxygen atom, its correct formula is HClO, not HClO2 which represents a different acid (chlorous acid).