# 106.3.2.32 TM-32, Determination of Purity of Sodium Chloride

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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) = ${\displaystyle 100\times {\frac {A\times C\times 584.5}{D}}}$

Where:

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