What is Mercuric nitrate method for chloride determination in water?
Reagents and Indicators R-13-1Analytical Methods of the Member Companies of theCorn Refiners Association, Inc.Accepted 4-15-86MERCURIC NITRATE SOLUTIONPREPARATION0.02N Mercuric Nitrate Solution: For chloride determination. Dissolve 3.3 g ofreagent grade mercuric nitrate (Hg(NO3)2) in about 100 mL of purified watercontaining 0.25 mL of concentrated nitric acid (70% HNO3, sp g 1.42). Dilute to1 L with purified water, and mix.STANDARDIZATIONDry a quantity of analytical grade sodium chloride (NaCl) 30 minutes at 105°C;cool in desiccator. Dissolve 0.8241 g of dry sodium chloride in purified water,dilute to 1 L volume, and mix.Pipet 5.00 mL of the above sodium chloride solution, containing 2.5 mg chloride,into each of three 250 mL glass stoppered Erlenmeyer flasks. Add 85 mL ofpurified water, 10 mL of diphenylcarbazone indicator solution, 1 mL of 30%hydrogen peroxide solution, and 1.0 mL of 0.5N nitric acid solution (Note 1) toeach of the flasks. Stopper flasks and swirl contents. Prepare a reagent blank in a250 mL Erlenmeyer flask containing 90 mL of purified water, 10 mL ofdiphenylcarbazone indicator solution, 1 mL of 30% hydrogen peroxide solution,and 1.0 mL of 0.5N nitric acid solution; mix. Titrate the blank with mercuricnitrate solution to the purple indicator end point. Color development near the endpoint is slow, and as much as 30 seconds should be allowed between titrant dropsto facilitate full indicator color development (Note 2). Titrate the three standardsin the same manner to the same color end point. Observe and record the titers.Calculate average normality.CALCULATION(mL Hg(NO ) Titer - Blank)×35.452.5mgNormality =3 2Reagents and Indicators R-13-2MERCURIC NITRATE SOLUTION⎯ continuedNOTES AND PRECAUTIONS1. Treatment with hydrogen peroxide destroys interfering sulfites by oxidationto sulfates, and the nitric acid addition adjusts acidity to the proper level(pH about 2.5).2. Care should be exercised as the end point is approached, and it is expedientto observe the reaction mixture over a white surface. End point detection isfacilitated by running the blank first, and then titrating the standards tomatch the color of the blank.
