Titration is a method for determining the unknown concentration of an analyte (Titrand) using a solution of known concentration (Titrant). The titrant is typically added to a known amount of the analyte using a burette until the reaction is completed. Often, a visual indicator is used to indicate the end-point of a reaction. Since the volume of the titrant is already known, the concentration of the analyte can be easily determined using the titration formula.
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What is half equivalence point?
The half equivalence point is the midway point between the equivalence point and the starting point in a titration. It is also known as the midpoint of titration. At this moment, the pH of the analyte solution is equal to the dissociation constant, or pKa, of the acid employed in the titration. The half equivalence point happens at one-half the volume of the first equivalence point.
If there are several equivalence points in the titration, the same number of half equivalence points exists. For example, the second-half equivalence point occurs between the first and second equivalence points. Because, at the half equivalence point, the pKa of the acid is equal to the pH of the solution, determining the half equivalence point is rather simple.
What is the equivalence point?
The equivalency point is also known as a stoichiometric point, it is the point in the titration process where the chemical reaction in the titration mixture ends. In a titration, the equivalence point is the actual point of the desired chemical reaction in the reaction mixture.
Typically, titrations are used to determine the concentration of a substance in a sample solution. The equivalence point can be determined by the pH change, color change, precipitation formation, temperature change, conductivity change, etc..
Difference between equivalence point and half equivalence point:
The major difference between the half equivalence point and equivalence point is that the half equivalence point is the midpoint between the beginning point and equivalence point of a particular titration, whereas the equivalence point is the point where the chemical reaction between titrant and titrand ends.
Frequently Asked Question (FAQ):
What does the half equivalence point mean?
The half equivalence point is where exactly half of the acid in the buffer solution has reacted with the titrant.
Are there two equivalence points with diprotic acid?
Yes, the number of equivalence points on a titration curve for a polyprotic acid corresponds to the number of acidic protons in the acid. Since a diprotic acid is titrated using two acidic protons, the titration curve contains two equivalence points.
Why is the pH equal to the pKa at the half equivalence point?
At the half-equivalence point, half of the acid is neutralized; therefore the amount of salt produced is half that of the acid; the concentrations of salt and acid are equal. Now, this solution is a buffer solution, and when the Henderson-Hasselbalch equation is used, the log value becomes zero.
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