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Determination of Acidity of Water – Environmental Engineering Lab Experiment

Determination of Acidity of Water – Lab Experiment

Acidity in water refers to the presence of substances that can neutralize bases. It is mainly caused by dissolved carbon dioxide, mineral acids, and salts of strong acids with weak bases. Determining the acidity of water is important for evaluating water quality and its suitability for drinking or industrial use.

The acidity of water is generally expressed in terms of milligrams per liter (mg/L) as CaCO₃.

Aim

To determine the acidity of the given water sample by titration using a standard alkali solution.

Apparatus Required

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

Chemicals Required

  • Standard sodium hydroxide (NaOH) solution
  • Methyl orange indicator
  • Phenolphthalein indicator
  • Distilled water

Theory

Acidity in water is determined by titrating the water sample with a standard solution of sodium hydroxide. During the titration, indicators such as methyl orange and phenolphthalein are used to detect the end point.

Acidity may be classified as:

  • Methyl orange acidity
  • Phenolphthalein acidity

These measurements help identify the presence of strong acids, weak acids, and dissolved carbon dioxide in water.

Procedure

  1. Take a known volume (usually 50 mL or 100 mL) of the water sample in a conical flask.
  2. Add a few drops of methyl orange indicator.
  3. Titrate the sample with standard sodium hydroxide solution until the color changes from red to yellow.
  4. Note the burette reading.
  5. Add phenolphthalein indicator to the same sample.
  6. Continue titration until the solution turns faint pink.
  7. Record the final burette reading.

Observation Table

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

Calculation

Acidity (mg/L as CaCO₃) =

(A × N × 50,000) / V

Where:

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

Result

The acidity of the given water sample was determined by titration with sodium hydroxide.

Acidity of the sample = ______ mg/L as CaCO₃

Precautions

  • Use clean and dry glassware.
  • Read the burette carefully to avoid parallax error.
  • Add indicators in small quantities.
  • Perform titration slowly near the end point.

Conclusion

The experiment helps determine the acidity level of water. This information is useful for assessing water quality and deciding suitable treatment methods before use.

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