IIT JEE , AIEEE Forum - Chemistry , Inorganic Chemistry

kvenkan

what is the difference btween end point & equivalence point in titrations?

magiclko

in short and simple form

The term "equivalence point" means that the solutions have been mixed in exactly the right proportions according to the equation.

The term "end point" is where the indicator changes colour. As you will see on the page about indicators, that isn't necessarily exactly the same as the equivalence point

in detail form

When you carry out a simple acid-base titration, you use an indicator to tell you when you have the acid and alkali mixed in exactly the right proportions to "neutralise" each other. When the indicator changes colour, this is often described as the end point of the titration.

In an ideal world, the colour change would happen when you mix the two solutions together in exactly equation proportions. That particular mixture is known as the equivalence point.

For example, if you were titrating sodium hydroxide solution with hydrochloric acid, both with a concentration of 1 mol dm^-3, 25 cm³ of sodium hydroxide solution would need exactly the same volume of the acid - because they react 1 : 1 according to the equation

In this particular instance, this would also be the neutral point of the titration, because sodium chloride solution has a pH of 7.

But that isn't necessarily true of all the salts you might get formed.

For example, if you titrate ammonia solution with hydrochloric acid, you would get ammonium chloride formed. The ammonium ion is slightly acidic, and so pure ammonium chloride has a slightly acidic pH.

That means that at the equivalence point (where you had mixed the solutions in the correct proportions according to the equation), the solution wouldn't actually be neutral. To use the term "neutral point" in this context would be misleading.

Similarly, if you titrate sodium hydroxide solution with ethanoic acid, at the equivalence point the pure sodium ethanoate formed has a slightly alkaline pH because the ethanoate ion is slightly basic.

arun-rashi

the standard solution is usually added from a long graduated tube called a burette.the point at which standard solution exactly neutralise unknown called equivelence point.this completion of titration indicated by some physical change or colour change by indicator known as end point.for example penolpthlein at end point shows pink colour while methyl orange show red colour from yellow.in the ideal titration the visible end point will coincide with the stichiometric end point.the indicator and the exp. condition should be selected that the difference between the visible end point and the eq point is as small as possible.

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