How does the hydrogen ion (H+) [or the hydronium ion (H3O+)] and the hydroxide i

Hydrogen ion may come from decomposition of an acid if the reaction occurs in acidic medium, and OH- ion may come from a base in similar way apart from these two medium we can have these ions comes from the decomposition of water, which comes from the medium in which we perform the reaction. there role in the reaction may differ from what we want let say we want to remove any ion which and we know it forms a stable compound with H+ ion so we take H+ ion in reaction to remove it similarly for any base used reaction.

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