1. What exactly is EDTA-Cu?
It is a stable chelate formed between copper(II) ions and ethylenediaminetetraacetic acid (EDTA). The most common commercial form is Copper Disodium EDTA (CAS No. 14025-15-1), used primarily as a micronutrient source.
2. What is the chemical formula and molecular weight?
Common formula: C₁₀H₁₂CuN₂Na₂O₈·xH₂O.
Anhydrous MW: ~397.75 g/mol.
It typically appears as a blue-green crystalline powder.
3. What is the stability constant (log K) of Cu-EDTA?
The conditional stability constant (log K) for Cu-EDTA is approximately 18.8.
This high value indicates a very strong bond, preventing the copper from precipitating as hydroxides or carbonates across a wide pH range.
4. How does EDTA-Cu differ from Copper Sulfate (CuSO₄)?
Unlike CuSO₄, which reacts with phosphate or hydroxide to form insoluble precipitates, EDTA-Cu remains soluble and bioavailable in neutral to alkaline soils (pH 4–9). It has higher absorption efficiency and lower risk of phytotoxicity (burning plants).
5. What is the solubility of EDTA-Cu in water?
It is highly soluble in water (approx. 1200 g/L at 20°C). It is generally insoluble in organic solvents like ethanol or acetone. A 1% solution usually has a pH between 5.0 and 7.0.
6. Why is EDTA-Cu used in agriculture?
It is used to correct copper deficiency in crops (e.g., wheat, citrus, vegetables). It ensures efficient uptake through leaves (foliar spray) or roots (fertigation) without interacting negatively with other nutrients like phosphorus.
7. How do you prepare a Cu-EDTA solution in the lab?
Dissolve equimolar amounts of Na₂EDTA and CuSO₄·5H₂O in water. Heat gently while stirring, adjust the pH to ~5–6 using NaOH or NH₄OH, and allow the complex to crystallize upon cooling.
8. How is EDTA-Cu analyzed or titrated?
By complexometric titration. At pH 5–6 (using an acetate buffer), Cu²⁺ is titrated with a standard EDTA solution using indicators like PAN (turns yellow at endpoint) or Xylenol Orange.
9. Is EDTA-Cu safe? What are the handling precautions?
It is classified as low toxicity but contains heavy metals. Avoid inhalation of dust. Wear gloves and safety goggles. Store in a cool, dry place away from strong acids or oxidizers. Do not discharge into waterways.
10. What are the industrial applications besides fertilizers?
Electroplating/Chemical Plating: As a stable copper source.
Water Treatment: To sequester metal ions and prevent scale.
Analytical Chemistry: As a standard reagent for calibration.
Textiles: As a dyeing auxiliary agent.