106.3.2.32 TM-32, Determination of Purity of Sodium Chloride

From Engineering Policy Guide
Jump to navigation Jump to search
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

This method determines the percent of sodium chloride in commercial grades of sodium chloride.

106.3.2.32.1 Reagents and Apparatus

a) Millivolt meter equipped with a combination chloride electrode.

b) Nitric Acid (HNO3), chloride free, 1.42 specific gravity.

c) Sodium Chloride (NaCl), Reagent Grade, dried at 105-110°C for 1 hour prior to use.

d) Silver Nitrate (AgNO3), Reagent Grade.

e) A source of chloride-free distilled or deionized water.

106.3.2.32.2 Preparation of Standard Solution

Standard Sodium Chloride Solution (0.0100N). Weigh 0.5844 g dried NaCl, dissolve in distilled water and dilute to 1L.

Standard Silver Nitrate Solution (0.01N). Weigh 1.699 g AgNO3, dissolve in distilled water and dilute to 1L. Standardize to the nearest 0.0001 N against 0.0100 N NaCl.

106.3.2.32.3 Procedure

Using a suitable sample splitting technique, divide the salt, as received, to obtain a representative sample of about 75 g. Dry at least 3 hours at 105-110C and cool to room temperature in a dessicator. Weigh the sample to the nearest 0.1 mg and transfer to a 1000-mL beaker. Add approximately 500 mL of distilled water and 20 mL of HNO3. Heat near boiling 1 hour, occasionally stirring and crushing any insoluble matter against the bottom of the beaker with the flattened end of a stirring rod. Cool to room temperature, quantitatively transfer to a 1000-mL volumetric flask and dilute to volume with distilled water. Transfer a 10-mL aliquot to a 1000-mL volumetric flask and dilute to volume with distilled water. Transfer a 10-mL aliquot to a 250-mL beaker, adding 90 mL of distilled water and 1 mL of HNO3. Determine the chloride concentration by potentiometric titration with the standard silver nitrate solution.

106.3.2.32.4 Calculation and Report

Report percent sodium chloride to the nearest 0.1% as follows:

% Sodium Chloride (NaCl) =

Where:

A = Milliliters of AgNO3 solution to titrate sample
C = Normality of AgNO3 solution
D = Grams of sample