Determination of Hardness of Water
- Take the Water Sample
- Take 25 mL of the water sample in a clean conical flask.
- Add Ammonia Buffer Solution
- Add 4-5 drops of Ammonia Buffer Solution.
- Add EBT Indicator
- Add 1-2 drops of EBT (Eriochrome Black T) Indicator.
- Titrate with EDTA 0.01 M
- Observe the End Point
- Continue adding EDTA until the color changes to light blue.
- The light blue color indicates the end point of the titration.
- Record the Burette Reading
- Record the total amount of EDTA used in mL.
Calculation of Total Hardness
When using:
Water Sample = 25 mL
EDTA Concentration = 0.01 M
The calculation is:
Total Hardness (mg/L as CaCO₃) = EDTA Used (mL) × 40
Example
If 3 mL of EDTA is used:
Total Hardness = 3 × 40 = 120 mg/L
FAQ on Determination of Hardness of Water
What is Water Hardness?
Water hardness is the presence of dissolved Calcium (Ca²⁺) and Magnesium (Mg²⁺) salts in water. The higher the concentration of these minerals, the harder the water becomes. Water hardness is commonly measured as mg/L or ppm as CaCO₃.
Why is Water Hardness Important?
Water hardness is important because it affects water quality and industrial processes. High hardness can cause scale formation in pipes, boilers, and equipment, while proper hardness control helps maintain consistent product quality and efficient operation.
Why is Ammonia Buffer Solution Added During the Water Hardness Test?
Ammonia Buffer Solution is added to maintain the water sample at a suitable pH of approximately 10. It provides the proper conditions for the EBT indicator and EDTA to react correctly with Calcium and Magnesium ions. This helps produce a clear and accurate color change at the endpoint during titration.
What Happens If the pH Is Below or Above 10 During the EDTA Water Hardness Test?
During the EDTA hardness test, the pH should be maintained at approximately 10 for accurate results. If the pH is too low, the EBT indicator may not give a clear color change, and the EDTA reaction may be incomplete. If the pH is too high, Calcium or Magnesium may start forming precipitates, which can also affect the titration result. Therefore, maintaining the correct pH is important for an accurate hardness measurement.
What Is EBT Indicator and What Does EBT Stand For?
EBT stands for Eriochrome Black T. It is a chemical indicator used in the EDTA water hardness test to detect Calcium and Magnesium ions. When EBT is added to the water sample, it usually produces a wine-red color in the presence of hardness minerals. During titration, the color changes to blue at the endpoint, indicating that the reaction is complete.
What Is EDTA, What Does EDTA Stand For, and Why Is It Used in Water Hardness Titration?
EDTA stands for Ethylenediaminetetraacetic Acid. It is a chemical solution used in the water hardness test to measure Calcium and Magnesium ions. EDTA binds with these hardness minerals during titration, and when all the Calcium and Magnesium have reacted, the indicator changes color from wine red to blue, showing the endpoint.