Various analytical methods can estimate the concentration of sodium chloride (NaCl) in a sample. One of the most common methods for estimating sodium chloride is titration. In this method, we use a standard solution of silver nitrate (AgNO3) as the titrant, and the formation of a white precipitate of silver chloride (AgCl) indicates the endpoint of the titration.
Here’s a simplified step-by-step procedure for estimating sodium chloride using silver nitrate titration:
Required Equipment and Reagents:
1. Sodium chloride sample
2. Silver nitrate (AgNO3) solution of known concentration
3. Potassium chromate (K2CrO4) indicator solution
4. Distilled water
5. Burette
6. Conical flask
7. Glass stirring rod
Procedure:
1. Prepare a sample solution by dissolving a known mass of the sodium chloride sample in distilled water. The sample should be accurately weighed.
2. Add a few drops of potassium chromate (K2CrO4) indicator solution to the sample solution. The indicator imparts a yellow color to the solution.
3. Fill the burette with the standardized silver nitrate (AgNO3) solution.
4. Titrate the sample solution by slowly adding the silver nitrate to the sample while stirring continuously. A white precipitate of silver chloride (AgCl) forms as silver ions react with chloride ions in the sample. The reaction is represented as Ag⁺ + Cl⁻ → AgCl↓.
5. Add the silver nitrate solution until you reach the endpoint. Detect the endpoint when you observe the appearance of the first faint and persistent reddish-brown color, signifying the formation of silver chromate (Ag2CrO4) due to the excess of silver ions.
6. Record the volume of the silver nitrate solution required to reach the endpoint. This volume is used for calculations.
Calculations:
You can calculate the sodium chloride (NaCl) concentration using the stoichiometry of the reaction. The amount of AgNO3 added (in moles) equals the amount of chloride ions (Cl⁻) in the sample. The concentration of NaCl is then calculated based on the volume of AgNO3 used.
