Question

For strong acid/strong base why is the initial region flat? Why does the curve rise suddenly? What is special about the center point of the rapidly rising region? Why is the region after the rapid rise flat?

Answer 1

This is the Titration Curve for Strong Acid vs Strong Base-

[Imporatant things in the Curve is to note the Starting point is around pH=2 , Equivalence point between pH=6-8 and end point beyond pH=10 which are in difference from any other titration curve]

• Initial Region:

Flat because Analyte has majority of ions as it is a strong acid,,we JUST started adding strong base dropwise so the displacement reaction has started where the ions are slowly replacing the   ions, and the pH is increasing gradually,in the graph,it is the region of pH 2-4.

• Sudden Rise of the Curve and Speciality of the Center point(R) of rapidly rising curve-

The point Q in the curve represents such a situation just before equilibrium,and after this point,addition of a SINGLE DROP OF STRONG BASE we directly get point 'R' where and we are at equilibrium as

no. of moles of the analyte strong acid=no of moles of the titrant strong base

and here the ions are completely neutralised and no further ions left,so we see a sudden jump in the curve.

• After Rapid Rise-

As we continue to add the strong base dropwise,there is now ions in excess and it finds no ion to 'eat' so the pH also rises gradually as we continue adding strong base, giving a rather flat region in curve after point 'S'.