Titrimetric analysis is classified into four main categories based on the type of reactions involved. Neutralization or acid-base titrations involve the reaction of a proton with a hydroxide ion to form a water molecule. In acidimetry, a basic analyte is titrated with a standard solution of a strong acid. In contrast, alkalimetry involves the titration of an acidic analyte with a standard solution of a strong base. In redox titrations, the oxidation number of the titrant and the analyte changes as electrons are transferred from the reducing to the oxidizing agent. In complexometric titrations, the titrating ligand reacts with the metal ion analyte, to form a metal–ligand complex. Lastly, in precipitation titrations, the analyte and titrant react to form a precipitate.