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Conductometric titration of strong acid and weak acid against strong base

Aim

To Determine Normality of acids in a given mixture by conductometry

Principle

Hydrochloric acid is a strong acid, acetic acid is a weak acid and sodium hydroxide is a strong base. The strength of HCL and acetic acid in the mixture can be determined by titrating it directly with sodium hydroxide. Upon adding a strong base to the mixture of strong acid and a weak acid, the conductance falls until the strong acid is neutralized, then rises as the weak acid is converted into its salt, and finally rises more steeply as the excess alkali is introduced

Procedure

For Strong acid contents determination.

  1. Wash and dry all glasswares as per standard laboratory procedure.
  2. Rinse all glasswares with distilled water.
  3. Rinse the burette with small portion of NaOH solution and fill the burette with standard NaOH solution.
  4. Add 50 ml of mixture of hydrochloric acid and acetic acid or unknown sample of given acid mixture in a beaker.
  5. Immerse the platinum electrodes in this solution (add some distilled water if sample amount is small).
  6. Note the initial conductance of sample before starting titration.
  7. Add       ml NaOH at a time from burette and note down the change in conductance after each ml.
  8. Continue until the conductance value after falling once starts increasing (end point).
  9. Plot the graph between conductance vs.volume of NaOH added.
  10. The Point of intersection between two curves indicates the end point of titration.

Reference

Indian Pharmacopoeia, Govt. of India, 2007, Volume 1, P- 115

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