Conductometric titration of strong acid against a strong base
Aim
To Determine Normality of given acid by conductometry
Principle
Hydrochloric acid is a strong acid and sodium hydroxide is a strong base. The strength of HCL can be determined by titrating it directly with sodium hydroxide. The conductance first falls due to the replacement of the hydrogen ion (Δ∞350) by the added cation (Δ∞ 40-80) and then after the equivalence point has been reached, rapidly rises with further addition of strong alkali due to the large values of the hydroxyl ion (198). The two branches of the curve are straight lines provided the volume of the reagent added is negligible and their intersection gives the endpoint (curves 1 and 2)
Procedure
For Strong acid content determination
- Wash and dry all glasswares as per standard laboratory procedure.
- Rinse all glasswares with distilled water.
- Rinse the burette with small portion of NaOH solution and fill the burette with standard NaOH solution.
- Add 50 ml of hydrochloric acid or unknown sample of given strong acid in a beaker.
- Immerse the platinum electrodes in this solution (add some distilled water if sample amount is small).
- Note the initial conductance of sample before starting titration.
- Add ml NaOH at a time from burette and note down the change in conductance after each ml.
- Continue until the conductance value after falling once starts increasing (end point).
- Plot the graph between conductance vs. volume of NaOH added.
- The point of intersection between two curves indicates the end point titration.
Reference
Indian Pharmacopoeia 2007, Volume 1, Pg no 115.
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