In an acid-base titration, 0.1 M HCl solution was added to the NaOH solution of unknown strength. Which of the following correctly shows the changes of pH of the titration mixture in this experiment?

(1) 

(2) 

(3) 

(4) 

Concept:

The Graph 1 and 2 both represents the titration curve between strong acid and strong base, that is HCl (Hydrochloric acid) and NaOH (Sodium Hydroxide). Initially, the pH of NaOH is more than 7 but during the titration, it decreased. So, graph (1) is correct.

In a strong acid-strong base titration, the acid and base will react to form a neutral solution. At the equivalence point of the reaction, hydronium (H⁺) and hydroxide (OH^-) ions will react to form water, leading to a pH of 7. This is true for all strong acid and strong base titrations.

The titration of hydrochloric acid (strong acid) and sodium hydroxide (strong base) to form sodium chloride and water. The reaction as follows,

NaOH + HCl ⟶ NaCl + H₂O

In a weak base-strong acid titration, the acid and base will react to form an acidic solution. A conjugate acid will be produced during the titration, which then reacts with water to form hydronium ions. This results in a solution with a pH lower than 7.

A strong acid is an acid that is completely dissociated or ionized in an aqueous solution. It is a chemical species with a high capacity to lose a proton H⁺. In water, a strong acid loses one proton, which is captured by water to form the hydronium ion.