Determination of Cl- ions: complexometric/colorimetric titration with Hg2+
Procedure
- Sample 50 mL of the water to be analyzed and transfer it to a 100 mL beaker.
- Successively add 5 drops of bromophenol blue and 5 drops of diphenyl carbazone.
- Adjust the pH to approximately 2.8 with the nitric acid solutions at 0.5 mol/L and 0.05 mol/L, proceeding as follows: neutralize with the concentrated acid until the indicator turns yellow, then add 1 mL of nitric acid at 0.05 mol/L.
- Titrate with the mercuric solution at 0.0142 N using a burette. The end-of-titration is reached when the solution turns from light yellow to purple.
- Carry out a blank test, operating as explained and replacing the test sample by distilled water. A few drops of mercuric solution should suffice to change the color.
≈ 20 minutes / sample