A back titration is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent whereas a direct titration directly measures the concentration of the unknown compound. The addition of excess reagents is not done as in back titrations. The unknown compound is directly reacted with the known compound. A back titration may also be called an indirect titration. The back titration is applied in the below scenarios.
- When the acid or (more commonly) base is an insoluble salt (e.g., calcium carbonate)
- When direct titration endpoint would be hard to discern (e.g., weak acid and weak base titration)
- When the reaction occurs very slowly
Two steps are typically followed in a back titration:
- The volatile analyte is permitted to react with an excess reagent
- A titration is conducted on the remaining quantity of the known solution
One way to measure the amount consumed by the analyte is this titration, then calculate the excess quantity.