Construction of a titration curve (Neutralization curve)

The mechanism of neutralization process can be understood by studying the changes in the hydrogen ion concentration during the course of the approximate titration. The change in pH in the vicinity of the equivalence point is of greatest importance as it enables an indicator to be selected with smallest titration error.

The curve (pH vs the moles of base or acid added) may be evaluated experimentally by determination of the pH at various stages during the titration by a potentiometric method or by usage of universal indicator.

Universal indicator is a mixture of suitable indicators which gives a color change over a considerable portion of pH range. They are not suitable for quantitative titrations, but may be employed for the determination of approximate pH of a solution.

Procedure

Pipette out 25.00 mL of the solution A into a titration flask and add few drops of the universal indicator. Compare the color with the color chart and record the corresponding pH value of the solution. Fill the burette with the solution B. Add following amounts (X) of solution B from the burette to the flask and record the corresponding pH value after each addition by comparing the color charts provided.

X mL = 12.50, 18.50, 22.50, 24.50, 24.75, 24.80, 24.85, 24.90, 24.95, 25.00, 25.05 25.10,25.15, 25.20, 25.25, 25.30, 25.35, 25.40, 25.45, 25.50, 27.50, 31.50 37.50, 42.50, 50.00

(i) Construct the titration curve using your results
(ii) Thus obtain the ideal pH range for an indicator
(iii) Suggest possible indicators which could be used in this titration



NOTE:-

You can use a pH meter instead of the universal indicator. Follow the same procedure usingthe pH meter and construct the titration curve. You can find the equivalence point in this curve which is the exact pH (a point) the neutralization takes place. When you use the indicators it is a pH range what you get, not the exact point.