What is Mercuric nitrate method for chloride determination in water?

Answer 1

Reagents and Indicators R-13-

1

Analytical Methods of the Member Companies of the

Corn Refiners Association, Inc.

Accepted 4-15-86

MERCURIC NITRATE SOLUTION

PREPARATION

0.02

N Mercuric Nitrate Solution: For chloride determination. Dissolve 3.3 g of

reagent grade mercuric nitrate (Hg(NO

3)2) in about 100 mL of purified water

containing 0.25 mL of concentrated nitric acid (70% HNO

3, sp g 1.42). Dilute to

1 L with purified water, and mix.

STANDARDIZATION

Dry 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 of

purified water, 10 mL of diphenylcarbazone indicator solution, 1 mL of 30%

hydrogen peroxide solution, and 1.0 mL of 0.5

N nitric acid solution (Note 1) to

each of the flasks. Stopper flasks and swirl contents. Prepare a reagent blank in a

250 mL Erlenmeyer flask containing 90 mL of purified water, 10 mL of

diphenylcarbazone indicator solution, 1 mL of 30% hydrogen peroxide solution,

and 1.0 mL of 0.5

N nitric acid solution; mix. Titrate the blank with mercuric

nitrate solution to the purple indicator end point. Color development near the end

point is slow, and as much as 30 seconds should be allowed between titrant drops

to facilitate full indicator color development (Note 2). Titrate the three standards

in the same manner to the same color end point. Observe and record the titers.

Calculate average normality.

CALCULATION

(mL Hg(NO ) Titer - Blank)×35.45

2.5mg

Normality =

3 2

Reagents and Indicators R-13-

2

MERCURIC NITRATE SOLUTION

⎯ continued

NOTES AND PRECAUTIONS

1. Treatment with hydrogen peroxide destroys interfering sulfites by oxidation

to 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 expedient

to observe the reaction mixture over a white surface. End point detection is

facilitated by running the blank first, and then titrating the standards to

match the color of the blank.

Answer 2

The Mercuric nitrate method for chloride determination involves adding mercuric nitrate to a water sample containing chloride ions, followed by the addition of potassium chromate as an indicator. The chloride ions form a white precipitate with mercuric ions, which is then titrated with silver nitrate solution to determine the concentration of chloride ions in the sample.