Equivalence Point Equivalence Point The equivalence point, or stoichiometric point, of a chemical reaction is when a titrant is added and is stoichiometrically equal to the number of moles of substance (known as analyte) present in the sample: the smallest amount of titrant that is sufficient to fully neutralize or react with the analyte. In some cases there are multiple equivalence points which are multiples of the first equivalent point, such as in the titration of a diprotic acid. A graph of the titration curve exhibits an inflection point at the equivalence point—where the graph is steepest. A striking fact about equivalence is that in a reaction the equivalence of the reactants as well as products is conserved. pH indicator :- Indicator play an important role in acid-base titration. They show a color change at equivalence point. They can be used in Redox titration. pH indicators give an approximation of the equivalence point. Potentiometer :- It is an instrument which can measure the electrode potential of the given solution and generally used in redox titration as the potential gets change at equivalence point in redox reactions.
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pH meter :- Just like pH indicators , they also show a variation in potential at change in pH. Conductance :- In acid-base titration, the equivalence point reached at neutralization point. Due to neutralization reaction the concentration of ions get change which associated with the change in conductance. Hence the change in conductance is the measurement of equivalence point. Color change :- Some reaction show color change at equivalence point without any added indicator. Precipitation :- In some titration process, a precipitate formed at equivalence point. For example; white precipitate of silver chloride formed because of reaction between Ag+ and Clat equivalence point. Isothermal titration calorimeter :- This is used to measure the heat produced or consumed by the reaction for the determination the equivalence point. Thermometric titrimetry :- In this technique the equivalence point is determined by using the rate of temperature change. Spectroscopy :- This method is based on the spectrum of the reactant, titrant or product. By using the spectrum the relative amounts of the product and reactant determine which used to calculate the equivalence point. Amperometry :- This technique is only can be used for amperometry titration. End Point :1. From the name only, we can conclude that end point is related to the end of titration in practice.
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2. The accuracy of titration will be high when the end point is quite close to the equivalence point. 3. For example in acid-base titration of a strong acid with a strong base, the equivalence point is at pH 7.00. 4. The indicator used for this titration is phenolphthalein which starts the color change at pH slightly above 8. 5. Hence, in this reaction the color change is noticed only when small excess amount added of titrant which introduces small positive error in the titration. 6. In other word both equivalence point and end point is different as equivalence point corresponds to the theoretical completion of the reaction while the endpoint is related to the actually measured physical change in the solution determined by an indicator or an instrument mentioned above.
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