4. Which of standard substance (or standardized solution) is correct for standardization of EDTA: 1) Silver nitrate solution; 2) Potassium permanganate solution : 3) Sodium chloride solution; 4) Magnesium sulfate solution : 5)Aminobenzenesulphonic acid solution. Explain your answer. Provide theoretical /practical information as much as you can (examples, chemicals reactions, etc.)

The correct answer is 4) Magnesium sulfate solution.<br /><br />EDTA (ethylenediaminetetraacetic acid) is a chelating agent that is commonly used for the determination of metal ions in solution. In order to standardize EDTA, a solution of a metal ion with a known concentration is required. Magnesium sulfate solution is commonly used for this purpose because it is a stable, easily prepared, and readily available solution of a metal ion that can react with EDTA in a well-defined stoichiometric reaction.<br /><br />The reaction between EDTA and magnesium ions is as follows:<br /><br />Mg2+ + EDTA4- → Mg-EDTA2-<br /><br />This reaction is highly selective and can be used to determine the concentration of magnesium ions in a solution. The stoichiometry of the reaction is 1:1, which means that one mole of EDTA reacts with one mole of magnesium ions. Therefore, by titrating a known volume of EDTA with a solution of magnesium sulfate of known concentration, the concentration of EDTA can be determined.<br /><br />The other options listed are not suitable for standardization of EDTA. Silver nitrate solution is not a primary standard because it is hygroscopic and can absorb moisture from the air. Potassium permanganate solution is a strong oxidizing agent and can react with EDTA in a redox reaction, which would interfere with the titration. Sodium chloride solution does not contain a metal ion that can react with EDTA in a well-defined stoichiometric reaction. Aminobenzer esulphonic acid solution is not a metal ion solution and therefore cannot be used for standardization of EDTA.