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Determination of Chlorides in Water – Environmental Engineering Lab Experiment

Determination of Chlorides in Water – Lab Experiment

Chlorides are commonly present in natural water and wastewater. They mainly occur in the form of sodium chloride, calcium chloride, and magnesium chloride. High chloride concentration in water can affect its taste and may cause corrosion in pipelines and boilers.

Therefore, determining the chloride content is important for evaluating water quality and suitability for drinking or industrial use.

Aim

To determine the chloride content in the given water sample by titration with a standard silver nitrate solution.

Apparatus Required

  • Burette
  • Pipette
  • Conical flask
  • Beakers
  • Measuring cylinder
  • Water sample

Chemicals Required

  • Standard silver nitrate (AgNO₃) solution
  • Potassium chromate indicator
  • Distilled water

Theory

The chloride content of water is determined by titrating the water sample with a standard solution of silver nitrate. During the titration, silver ions react with chloride ions to form silver chloride precipitate.

Potassium chromate is used as an indicator. After all chloride ions react with silver nitrate, the excess silver ions react with chromate ions to form a reddish-brown silver chromate precipitate, which indicates the end point of the titration.

Procedure

  1. Take a known volume (usually 50 mL) of the water sample in a conical flask.
  2. Add 2–3 drops of potassium chromate indicator.
  3. Titrate the sample with standard silver nitrate solution.
  4. Continue titration until the color changes to a reddish-brown shade.
  5. Record the burette reading.

Observation Table

Sample Volume (mL) Initial Burette Reading (mL) Final Burette Reading (mL) AgNO₃ Used (mL)
______ ______ ______ ______

Calculation

Chloride concentration (mg/L) =

(A × N × 35.45 × 1000) / V

Where:

  • A = Volume of AgNO₃ used (mL)
  • N = Normality of AgNO₃ solution
  • V = Volume of water sample (mL)

Result

The chloride content of the given water sample was determined using the silver nitrate titration method.

Chloride concentration = ______ mg/L

Precautions

  • Use clean and dry glassware.
  • Add the indicator in small quantities.
  • Perform titration slowly near the end point.
  • Record burette readings carefully to avoid errors.

Conclusion

The experiment helps determine the chloride concentration in water. This parameter is useful for evaluating water quality and identifying possible contamination from sewage, industrial waste, or saline sources.

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