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Determination of Alkalinity of Water – Environmental Engineering Lab Experiment

Determination of Alkalinity of Water – Lab Experiment

Alkalinity of water is the measure of its capacity to neutralize acids. It is mainly caused by the presence of bicarbonates, carbonates, and hydroxides in water. Determining alkalinity is important for evaluating water quality and the effectiveness of water treatment processes.

Alkalinity is generally expressed in milligrams per liter (mg/L) as CaCO₃.

Aim

To determine the alkalinity of the given water sample by titration with a standard acid solution.

Apparatus Required

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

Chemicals Required

  • Standard sulfuric acid (H₂SO₄) or hydrochloric acid (HCl)
  • Phenolphthalein indicator
  • Methyl orange indicator
  • Distilled water

Theory

Alkalinity in water is determined by titrating the water sample with a standard acid solution. Indicators such as phenolphthalein and methyl orange are used to detect the end points during the titration.

Alkalinity is classified into:

  • Phenolphthalein alkalinity (P-alkalinity)
  • Total alkalinity (M-alkalinity)

These values help identify the presence of hydroxide, carbonate, and bicarbonate ions 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 phenolphthalein indicator.
  3. If the solution turns pink, titrate with standard acid until the pink color disappears.
  4. Note the burette reading for phenolphthalein alkalinity.
  5. Add a few drops of methyl orange indicator to the same sample.
  6. Continue titration until the color changes from yellow to orange.
  7. Record the final burette reading.

Observation Table

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

Calculation

Alkalinity (mg/L as CaCO₃) =

(A × N × 50,000) / V

Where:

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

Result

The alkalinity of the given water sample was determined by titration with a standard acid solution.

Alkalinity 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 alkalinity level of water. This parameter is important for assessing water quality and maintaining proper conditions in water treatment processes.

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