ANALYTICAL cHEMISTRY - III

MSCM301

Experiment 3

Aim of the Experiment

Determination of acetic acid content of vinegar by conductometric titration.

Principle

  • This experiment is based on the principle of conductometric titrations. In this experiment, acetic acid is a weak acid. When it is titrated with a strong base like NaOH, initially the conductance is low due to the feeble ionization of acetic acid. On the addition of base, there is decrease in conductance not only due to the replacement of H+ by Na+ but also suppresses the dissociation of acetic acid due to common ion acetate.

  • But very soon, the conductance increases on adding NaOH as NaOH neutralizes the un-dissociated CH3COOH to CH3COONa which is the strong electrolyte. This increase in conductance continues raise up to the equivalence point. The graph near the equivalence point is curved due the hydrolysis of salt CH3COONa.

  • Beyond the equivalence point, conductance increases more rapidly with the addition of NaOH due to the highly conducting OH− ions. You will get a titration curve which resembles the one shown below. The point of intersection of the two lines gives the point of neutralization i.e., equivalence point.

Graph of conductometric titration showing equivalence point, I

Apparatus required

Conductometer, Pipette, Beaker, Burette, etc.

Chemicals required

Vinegar solution (30 mL in 100 mL standard calibrated flask), 0.1 M NaOH solution (which was standardized with standard oxalic acid solution).

Procedure

  • Pipette out 30 mL of vinegar solution from the flask in a 50 mL beaker and dip the conductivity electrode into it.

  • Take 0.1 M NaOH solution in the burette. Connect the conductometer to the mains and to the conductance cell.

  • Switch on the instrument. Calibrate the meter keeping the selector knob at ‘20 ms’ by rotating the ‘sensitivity’ knob till the meter reads 1.0.

  • Measure the conductance of the solution. Record this value. Make additions of 0.1 M NaOH solution from the burette as given in observation table.

  • After each addition, stir the solution well and read the conductance. Enter all the conductance data in observation table.

Determination of strength of Acetic acid in commercial vinegar by conductometric titration.mp4

Observation

Calculation

Result

  • Since 30 mL of the commercial vinegar sample is taken and diluted to 100 mL, so the molarity of the commercial vinegar = ____________ mol L−1

  • Formula weight of acetic acid is 60 g mol−1, hence, the strength of commercial vinegar = _____________ g L−1

Reference Material

  1. G H Jeffery, J Bassett, J Mendham and R C Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th Edition

Questions

  1. What is the prime requirement for any material to be conducting in nature?

  2. Discuss the factors that are affecting the conductivity of any material in its solution state.

  3. What kind of acid-base systems can be titrated using conductometry?

Developed by

Dr. Viraj Bhanvadia,

Assistant Professor, Chemistry,

viraj.bhanvadia@gsfcuniversity.ac.in