Back titration
Back titration is a type of analytical technique used in chemistry to determine the concentration of an unknown substance in a sample by reacting it with an excess of a known reagent and then determining the amount of excess reagent remaining after the reaction has taken place.
This technique is often used when the direct titration of the unknown substance is not possible or is challenging due to various factors such as the presence of impurities or a slow reaction rate. In back titration, the unknown substance is allowed to react with an excess of a known reagent, forming a new product. The excess reagent is then determined by titrating it with a second reagent of known concentration.
The steps involved in back titration are as follows:
1. A known amount of the unknown sample is taken and reacted with an excess of a known reagent. This reaction is allowed to proceed until completion.
2. Once the reaction is completed, the remaining excess reagent is then determined by titration with a second reagent of known concentration. This titration is usually performed with an indicator to detect the endpoint of the reaction.
3. From the volume of the second reagent required in the titration, the amount of excess reagent and thus the amount reacted with the unknown substance can be determined.
4. Finally, using stoichiometry, the concentration of the unknown substance in the sample can be calculated.
Back titration is particularly useful for substances that react slowly, react partially, or do not have a suitable direct titration method available. It can also be used to determine the concentration of substances that cannot be directly titrated due to interfering substances in the sample.
Overall, back titration allows for accurate determination of the concentration of an unknown substance in a sample by using an indirect measurement method.