Hi. We did an experiment on Quantitatve Determintion of Total Hardness in Drinking water by Complexometric EDTA Titration and I have a lot of questions.

1. What is the concept of complexometric titration and water hardness? (Why is it expressed in ppm CaCO3?)

2. Why is EDTA use as complexing agent and titrant?

3. Why is EBT use as an indicator? What is the significance of adding MgCl26H2O crystals to the titrant?

4. What are the other applications of EDTA complexation?

5. What is the rationale behind performing the analysis of Ca and Mg at pH 10?

thank you so much for your time.

These look very much like questions at the end of the experiment OR as a pre-lab exercise. If you want to winnow the list somewhat and give answers and reasons perhaps we can help but no one here will do your homework for you. Most of the answers can be found in any standard quant book dealing with EDTA titrations.

How can EDTA be used to estimate ca2+ or mg2+ in water

1. Complexometric titration is a type of titration where a complexing agent, such as EDTA (ethylenediaminetetraacetic acid), is used to form a complex with the analyte (the substance being analyzed), which can be a metal ion. In the case of water hardness, the analyte is typically calcium and magnesium ions.

Water hardness refers to the concentration of calcium and magnesium ions in water. It is expressed in terms of ppm (parts per million) CaCO3 (calcium carbonate) because calcium and magnesium ions are the main contributors to water hardness, and their concentrations are commonly reported as an equivalent concentration of calcium carbonate for simplicity.

2. EDTA is commonly used as a complexing agent and titrant in complexometric titrations due to its ability to readily form stable complexes with metal ions, including calcium and magnesium. EDTA has multiple electron-donating oxygen and nitrogen atoms, which can coordinate with metal ions, forming stable 1:1 complexes. This makes EDTA a suitable reagent for complexing metal ions in water hardness analysis.

3. EBT (Eriochrome Black T) is used as an indicator in complexometric titration because it undergoes a color change at the endpoint of the titration. EBT forms a red-colored complex with calcium ions, which changes to blue when EDTA complexation is complete.

The addition of MgCl26H2O crystals to the titrant helps to prevent the interference of other metal ions, particularly transition metal ions like iron and copper. These metal ions could also form complexes with EDTA, leading to incorrect results. The addition of magnesium ions helps to ensure that all interfering metal ions are complexed before the calcium and magnesium ions are titrated.

4. EDTA complexation has several other applications in analytical chemistry. It is widely used in metal ion analysis, such as determining the concentrations of other metal ions like iron, copper, zinc, and lead. EDTA is also used in the formulation of chelation therapy drugs, which are used to treat metal ion poisoning or to remove excess metal ions from the body.

5. The analysis of calcium and magnesium in water is typically performed at pH 10 because at this pH, other interfering metal ions like iron and copper are usually effectively complexed and do not interfere with the titration. Additionally, calcium and magnesium ions form strong complexes with EDTA at pH 10, ensuring accurate and precise titration results. The pH is controlled using a buffer solution to maintain the desired pH during the titration process.