In chemistry, titrimetric methods are broadly classified into three types: volumetric, gravimetric, and coulometric. Volumetric titrations involve measuring the volume of a titrant of known concentration that is required to react completely with an analyte. In gravimetric titrations, the standard solution reacts with the analyte to form an insoluble precipitate, which is filtered, dried, and weighed. In coulometric titrations, current is applied to an electrochemical reaction until the reaction is complete, and the charge required for this reaction is calculated to determine the amount or concentration of the reactant(s).
Generally, in titrations, a titrant with a known concentration is added to the analyte until the analyte is consumed, i.e. when the endpoint is reached. In this case, the process is called direct titration. In some cases, the reaction may be too slow for a sharp endpoint to be obtained. In such cases, back titration is used. In a back titration, the analyte is allowed to react with an excess amount of a standard solution, and the remaining quantity of this standard solution is titrated with a second standard solution. The exact amount of the first standard solution required to react with the analyte can then be calculated.
Sometimes, no suitable indicator can be found for either a direct or an indirect (back) titration. In this case, displacement titration can be used, in which the analyte displaces a reagent, usually from a complex, and the displaced reagent is measured by titration.
