Endpoint and equivalence points are often confused. Both are important stages of any titration experiment and have many differences. Like other titration terms such as titrants, analyte, burette, and pipette, endpoint and equivalence points are equally important in fully understanding the titration technique.
In a nutshell,
“Endpoint is the point in the titration process where the indicator changes its color whereas the equivalence point indicates the completion of the reaction between titrant (standard) and the substance being titrated (analyte).”
Endpoint vs equivalence point
The point at which color change i.e. (medium change) occurs in the system due to pH change is called endpoint
At equivalence point, the chemical reaction in the titration mixture ends
At this point, the moles of titrant exceed the moles of the analyte. A sharp change in pH occurs at this point resulting in color change of the indicator
It is the exact point in a titration when the number of moles of titrant are equal to the number of moles of analyte
It comes after equivalence point
It occurs before the endpoint
Titration is complete once the endpoint reaches
It does not indicate the completion of a titration process
Endpoint does not mean the completion of reaction between analyte and titrant
Equivalence point means the completion of reaction between titrant and analyte
It occurs once in a reaction
A titration process can have multiple equivalence points
Change in color
Just before change in color
What is endpoint?
Endpoint is a volumetric point, achieved by carefully administering the number of drops of titrant, as a single drop can change the pH of the solution. Light pink color appearance or complete transparence of pink color means the endpoint in titrations when the phenolphthalein indicator is used eitherwise.
Consider this example where hydrochloric acid (HCl) is titrated against sodium hydroxide (NaOH):
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
During the titration, NaOH is slowly added which results in neutralization with HCl or otherwise.
- At equivalence point, the reaction is supposedly complete. The pH at this point will be 7.0 as both the acid (HCl) and base (NaOH) are equal.
- Before equivalence point, the solution will be acidic as the excess of HCl remains in the flask or otherwise.
- After equivalence point, the solution will be basic having an excess of NaOH or otherwise.
This point where the basic environment turns the phenolphthalein indicator pink is called the endpoint in this case. As soon as, the light pink color appears, the titration is complete. The endpoint is reached and no further NaOH is added for this titration.
It should be noted that different indicators can be used depending on the type of solution being used for titration. Litmus paper, methyl orange, and phenolphthalein, etc are commonly used indicators in laboratories.
In addition to indicators, a pH meter or conductivity meter can also be used to signal the completion of the reaction. In a neutralization reaction between a strong acid and a strong base, a pH of 7 would indicate that the reaction is complete.
Sometimes, a situation may come where the endpoint is passed, the solution then could be made to perform back titration depending on the nature of the solution.
What is equivalence point?
Equivalence point indicates the completion of reaction where the number of moles of titrant equals the number of moles of analyte in the balanced chemical equation. In other words, exactly enough titrant has been added to react with all of the analyte.
For example, in the titration of NaOH and HCl, at the equivalence point, one mole of NaOH will be equal to one mole of HCl.
- For strong acid-strong base titrations, the equivalence point is at pH 7.
- The equivalence point for weak base-strong acid titrations is at a pH less than 7.
- In the case of weak acid-strong base titrations, the equivalence point is at pH above 7.
Titration of a base against an acid graph shapes like a rising curve. Initially, when the solution mixture is more acidic than basic, pH starts to rise gradually. After some volume of the base has been added, a point is reached which corresponds to the equal amount of acid and base in the mixture. This point is called equivalence point.
Titration of acid against a base is similar to the above one, except it has an opposite shape. Initially, when the mixture is just basic, the pH is high. Acid is added gradually into the base to nullify the basic effect. After some addition, a point arrives when the mixture seems to be neutral because the amount of acid and base is exactly equal.
If the titrant is kept being added to the mixture, the curves will proceed in an opposite manner to other pH sides, until the pH line becomes straight meaning that the whole mixture is now at the same pH level as the titrant.
Know more about pH calculations at the equivalence point here:
Main differences between endpoint and equivalence point
What is half equivalence point?
The half equivalence point is the point where half of the titrant needed for neutralization has been added to the flask form burette.
What is the difference between endpoint and stoichiometric point?
Stoichiometric point is another name of the equivalence point.
Why does endpoint occur after equivalence point?
The endpoint is the point where the indicator changes its color. The color change occurs at a point when the titration solution becomes basic. So after the complete neutralization at the equivalence point, the endpoint can be established.
Is the equivalence point always at pH 7?
When a strong acid neutralizes a strong base, the equivalence point is always at a pH 7. However, in the case of the reaction of weak acids with strong bases and weak bases with strong acids, the equivalence point is at pH > 7 and pH < 7 respectively.
Is endpoint the same as neutralization?
No. At the equivalence point, the neutralization reaction is complete. Whereas endpoint means the completion of the titration process or the indication of reaction completion.
What species are present at the equivalence point?
In acid-base titrations, salt and water are present at the point of equivalence.
What is the difference between the endpoint and equivalence point in a neutralization reaction?
The endpoint is simply the end of the titration reaction indicated by the change in color of the selected indicator. Whereas the equivalence point is a point at which exactly enough amount of titrant neutralizes the analyte.
How can you tell if you have exceeded the equivalence point in your titration?
Once you reach the endpoint, you can be sure that you have just passed the equivalence point. The titration mixture will have a pink color for (acid→base) or transparency for (base→acid), afterward, if the used indicator is phenolphthalein.
What is the midpoint of titration?
The point at which half of the analyte is neutralized by the added titrant is called the midpoint of titration.
Why do diprotic acids have two equivalence points?
Diprotic acids have two equivalence points. This is so because the two ionizing hydrogens do not dissociate from the acid at the same time.