Comparative Hl Titration Of Hcl

“Comparative pH titrations of strong and weak acids”

Experiment #6 – The aim of the experiment is to titrate a strong acid and a weak acid with a primary standard

solution NaOH and finding its pH. The titrant NaOH which is 1M is filled in the burette. Below

the titrant, a 250-ml beaker is positioned is such a way that while titrating the NaOH is poured

down the beaker which is filled with a solution of 75-ml of DI water and 25-ml of HCL. In order

to begin titration, the electrode is put into the beaker such that it doesn’t hit the spinning stir bar.

A magnetic stir bar is kept underneath the 250-ml beaker so that the mixture gets dissolved

faster. The pH is recorded on the instrument named pH meter which records the pH value.

Equivalence point is a point in

Figure 3 represents the data points for the 2nd trial of HCL and acetic acid.

Discussion –

Figure 1 – The initial pH of HCL without the titrant in the solution at 0.0 ml is 0.69. On adding

NaOH, the pH increases slowly and reaches the equivalence point at a pH of 7.1 and a volume

of 24.24 ml.

Figure 2 - For figure 2, the initial pH of acetic acid is 2.72 at 0.0 ml. The equivalence point for

acetic acid is at a volume of 24.75 ml with a pH of 8.95.

Figure 3 – On comparing the acids, the initial pH of acetic acid has a sharp increase at the

beginning of the titration curve, because the anion of the weak acid becomes a common ion that

reduces the ionization of the acid. Before equivalence point i.e., between 0% to 90% of the reaction, the pH for a weak acid increases gradually, because now the solution acts as buffer.

At this phase the solution is acidic. At the equivalence i.e., between 90% and 100% of the

reaction, the moles of acid are stoichiometrically equal to the moles of base. The equivalence

point for both HCL and acetic acid is 7.67 and 9.19 respectively. The volume at which