Question

Which of the following titration curves represents the titration of a strong base (in the Erlenmeyer flask) with a strong acid (in the burette)? 14 12 10 8 6 2 0 25 Volume of titrant added (mL) 14 12 10 8 6 4 2 0 0 25 Volume of titrant added (mL) 14 50 50 4 Hd Hd

Answer 1

Since the flask is containing base and from burette we are adding acid dropwise, the pH of the solution in flask is measured. So, it is obvious that the observed pH initially is that of alkalined solution and beyond equivalence point it is the pH of an acidic solution. So, pH curve should run from high to low. So, possible answer is either the first one or the fifth one.

In the 5th one the pH initially quickly decreases up to certain portion and then the extent of lowering suddenly decreases. It indicates there must be some resisting phenomenon occuring after certain volume of acid is added. Such resisting phenomenon is called buffering action. Which occurs in case of weak base-strong acid titration, because weak base and its conjugate acid makes a buffer solution which is resistive to pH change.

In case of strong base and strong acid pH titration, the decrease in pH should be uniform up to certain (no buffering action) extent. Then near equivalence point it shows a sharp decay and again after that it shows similar decrease in pH like before in uniform fashion. This characteristic is shown by the first titration curve. So, this is the answer.