Question

Explain in your own words why the region of a titration curve that has a slope closest to zero (the “flattest” part) is always halfway to the equivalence point when titrating either a weak acid or weak base. Make your explanation as specific and quantitative as possible.

Answer 1

Weak Acid and Weak Base titration:-

Let us suppose that that we take weak acid (W.A.) in tritration flask and weak base (W.B.) in burate (as we know weak acid do not give H⁺ ion easly) and weak base in burate. As we start titration we start adding W.B. in W.A. but at this time W.A. do not start react with W.B. because it do not give H⁺ ion easly so the curve is near to zero but after some time adding more base from the burate the quantity of base start increasing in flask ( here H⁺ ions start reacting with OH^- ions and form H₂O) and because of which acid start reacting with base or acid starts neutralise by the base. Now we see the curve start increasing from zero. But after some time we find out a stright line which indicate equalence point. Where all the H⁺ ions are comletely reacted with OH^- ions ( now pH=7 i.e. neutral ). After this equivalance point we start adding more W.B. in the flask the percentage of OH^- ions start increases in the flask and a curve start formed and after this curve the stright line is formed which shows that there is only OH^- ions are present in the flask ( i.e. W.B.).