How do you find the hardness of water experiment?

The hardness of water is typically determined through a titration experiment using a standard solution of EDTA (ethylenediaminetetraacetic acid).

Understanding Water Hardness

Water hardness primarily refers to the concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions dissolved in water. These ions interfere with the action of soaps and detergents and can cause scale buildup in pipes and appliances.

The EDTA Titration Method

The most common method for determining water hardness is titration with EDTA. EDTA is a complexing agent that binds strongly to calcium and magnesium ions. Since EDTA itself is not very soluble in water, the disodium salt of EDTA (Na₂H₂EDTA) is usually used.

Materials Needed:

• Water Sample: The water sample to be tested for hardness.
• EDTA Solution: A standard solution of EDTA of known concentration (typically 0.01 M).
• Buffer Solution: A buffer solution, typically ammonium chloride/ammonium hydroxide (NH₄Cl/NH₄OH), to maintain the pH at around 10. This pH is crucial for the indicator to function correctly.
• Indicator: An indicator such as Eriochrome Black T (EBT). EBT forms a wine-red complex with calcium and magnesium ions.
• Titration Apparatus: A burette, pipette, and conical flask.
• Distilled Water: For rinsing and preparing solutions.

Procedure:

1. Preparation:

   • Pipette a known volume (e.g., 50 mL or 100 mL) of the water sample into a conical flask.
   • Add a suitable amount (e.g., 1-2 mL) of the buffer solution to maintain the pH at approximately 10.
   • Add a few drops of the Eriochrome Black T indicator. The solution will turn wine-red if calcium and/or magnesium ions are present.

2. Titration:

   • Fill the burette with the standard EDTA solution.
   • Slowly add the EDTA solution from the burette to the water sample in the conical flask while continuously swirling the flask.
   • Continue adding EDTA until the solution changes color from wine-red to a permanent blue. This is the endpoint of the titration.

3. Calculations:

   • Record the volume of EDTA solution used to reach the endpoint.
   • Calculate the hardness of the water using the following formula:

   Hardness (mg/L as CaCO₃) = (Volume of EDTA used (L) × Molarity of EDTA × Molar mass of CaCO₃ × 1000) / Volume of water sample (L)

   Where:

   • Molar mass of CaCO₃ = 100.09 g/mol
   • 1000 is a conversion factor to express hardness in mg/L (ppm).

Example Calculation:

Let's say:

• Volume of water sample = 100 mL (0.1 L)
• Molarity of EDTA = 0.01 M
• Volume of EDTA used = 15 mL (0.015 L)

Then:

Hardness = (0.015 L × 0.01 mol/L × 100.09 g/mol × 1000 mg/g) / 0.1 L

Hardness = 150.135 mg/L as CaCO₃

This would be considered moderately hard water.

Interpreting Results:

The hardness of water is typically expressed in milligrams per liter (mg/L) as calcium carbonate (CaCO₃). Here's a common classification:

Hardness (mg/L as CaCO3)	Classification
0-60	Soft
61-120	Moderately Hard
121-180	Hard
>180	Very Hard

Precautions:

• Ensure all glassware is clean.
• Use distilled water for preparing solutions.
• Add the indicator just before the titration to minimize its decomposition.
• Swirl the flask continuously during the titration to ensure proper mixing.
• Titrate slowly near the endpoint for accuracy.

Conclusion

Determining water hardness through EDTA titration is a precise and commonly used method. By following the outlined procedure and calculations, you can accurately measure the calcium and magnesium ion concentration in your water sample and determine its hardness level.