How to identify an acid?

Like How do I know if HF is Hydrogen Fluoride or if its Hydrofluoric acid? And before some replies with the "AcIds have Hydrogen and bases have Hydroxide," No that doesn't help at all. H20 has hydrogen and isn't acid. But HI does have hydrogen and is acid. plus H2S04 could either be dihydrogen... show more Like How do I know if HF is Hydrogen Fluoride or if its Hydrofluoric acid? And before some replies with the "AcIds have Hydrogen and bases have Hydroxide," No that doesn't help at all. H20 has hydrogen and isn't acid. But HI does have hydrogen and is acid. plus H2S04 could either be dihydrogen Sulfate or sulfuric acid, how do I identify? By chemical formula
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