The major difference between back titration and direct titration is that in a back titration, an excess of standard titrant is added to the solute, and the excess titrant is titrated to determine how much is in excess, while in a direct titration, a standard titrant is added to the analyte until the endpoint is reached.
Titrations or titrimetry is a volumetric analysis technique for determining the amount of analyte contained in a sample. It involves a titrant that is in the burette, and we use a pipette to introduce the analyte to the conical flask. In the conical flask, the reaction takes place.
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The endpoint or equivalence point of any titration method is the point at which the reaction completes (Chemical equivalence point). An indicator that changes color at the endpoint can be used to detect the end-point. Alternatively, we can use a change in an instrumental response, for example, a potentiometer or conductivity meter, to determine the endpoint. Acid-base titrations, redox titrations, complexometric titrations, and precipitation titrations are four different forms of titrations, each involving different types of chemical reactions and principles.
What is back titration?
Back titration is a type of titration that may also be called an indirect titration that is performed in reverse. Instead of titration the original sample, a known excess of the standard reagent is added to the solution, and the excess is titrated. Back titrations are useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in an insoluble solid.
In a back-titration, an excess volume of the standard titrant is added to the analyte. The standard titrant will then react with the analyte, and the excess remains in the sample. A back-titration can be used to determine the remaining amount of standard reagent. Back titration example: determining phosphate concentration by titrating excess silver nitrate with potassium thiocyanate.
What is direct titration?
Direct titration is the most basic titration process which involves a reaction between unknown compounds with a known concentration compounds. This type of titration does not involve the addition of excess reagent; the unknown compound reacts directly with the known compound.
As a result, the titration's endpoint indicates the end of the reaction. The concentration of unknown substances contained in the sample solution can be determined using that endpoint. Direct titration example: Acid-base titrations are good examples of direct titrations.
Back vs direct titration
Difference between back titration and direct titration:
- The difference between back titration and direct titration is that a back titration estimates the unknown concentration by determining the remaining amount of known analytes, while a direct titration directly determines the concentration unknown of analytes.
- In a back titration, an excess of standard titrant is added to the solute, and the excess titrant is titrated to determine how much is in excess, while in a direct titration, a standard titrant is added to the analyte until the endpoint is reached.
- Back titrations are performed to determine the precise endpoint when there are sharp color changes of the solution, while direct titrations are performed when the titration's endpoint can be easily determined.
- In a back titration, two chemical reactions take place, while in a direct titration only one chemical reaction takes place.
- The titration is performed between two known analytes in back titration, while a known analyte is titrated against an unknown analyte in a direct titration.
- The remaining amount of reagent added in excess is the titrand of the back titration, while the unknown substance is the titrand of the direct titration.
When is a back titration used?
Back titration is particularly used when an acid or a base is an insoluble salt, one of the reactants is volatile, and a particular reaction is too slow, etc. When the molar concentration of an excess reactant is known, but the strength or concentration of a compound must be determined, back titration is performed.
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