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Determination of Hardness of Water – Environmental Engineering Lab Experiment

Determination of Hardness of Water – Lab Experiment

Hardness of water is mainly caused by the presence of dissolved salts of calcium and magnesium. Hard water forms scale in pipes and boilers and reduces the efficiency of soaps and detergents. Therefore, determining water hardness is important for assessing water quality and suitability for domestic and industrial use.

Hardness is usually expressed in terms of milligrams per liter (mg/L) as CaCO₃.

Aim

To determine the total hardness of the given water sample using the EDTA titration method.

Apparatus Required

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

Chemicals Required

  • Standard EDTA solution
  • Ammonia buffer solution
  • Eriochrome Black T indicator
  • Distilled water

Theory

The hardness of water is determined by titrating the water sample with a standard solution of EDTA (Ethylenediaminetetraacetic acid). EDTA forms stable complexes with calcium and magnesium ions present in water.

Eriochrome Black T indicator is used during the titration. The solution initially turns wine red. When all hardness-causing ions react with EDTA, the color changes to blue, indicating 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 1–2 mL of ammonia buffer solution.
  3. Add a small amount of Eriochrome Black T indicator.
  4. The solution will turn wine red in color.
  5. Titrate the sample with standard EDTA solution.
  6. Continue titration until the color changes from wine red to blue.
  7. Record the burette reading.

Observation Table

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

Calculation

Total Hardness (mg/L as CaCO₃) =

(A × N × 50,000) / V

Where:

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

Result

The hardness of the given water sample was determined using the EDTA titration method.

Total hardness of the sample = ______ mg/L as CaCO₃

Precautions

  • Use clean and dry glassware.
  • Add the indicator in small quantities.
  • Maintain proper pH using buffer solution.
  • Perform titration slowly near the end point.

Conclusion

The experiment helps determine the total hardness of water. This information is useful for evaluating water quality and deciding suitable treatment methods for domestic and industrial use.

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