EDTA·Na₄ (Ethylene Diamine Tetraacetic Acid Tetrasodium Salt) is a highly water-soluble and stable chelating agent. Below are the details of its solubility and stability:
1. Solubility
- Water Solubility:
- EDTA·Na₄ is highly soluble in water. At room temperature (25°C), its solubility is approximately > 100 g/100 mL of water.
- This high solubility makes it ideal for use in aqueous systems, such as water treatment, cleaning products, and laboratory solutions.
- pH Effect:
- The solubility of EDTA·Na₄ is further enhanced in alkaline conditions because it is already in its salt form (tetrasodium salt).
- Organic Solvents:
- EDTA·Na₄ is not soluble in most organic solvents (e.g., ethanol, acetone) due to its ionic nature.
2. Stability
EDTA·Na₄ is a stable compound under normal conditions, but its stability can be affected by environmental factors such as pH, temperature, and the presence of oxidizing agents.
A. Chemical Stability
- pH Stability:
- EDTA·Na₄ is most stable in alkaline conditions (pH ~ 11–12), which is the natural pH of its aqueous solutions.
- In acidic conditions (pH < 4), it may partially convert to free EDTA (acid form), which has lower solubility and chelating efficiency.
- Oxidation:
- EDTA·Na₄ is stable to mild oxidizing agents but can degrade under strong oxidizing conditions.
- Thermal Stability:
- It is thermally stable at moderate temperatures. However, prolonged exposure to high temperatures (above 100°C) may cause decomposition.
B. Stability in Complex Formation
- EDTA·Na₄ forms highly stable complexes with metal ions, with stability constants (log K) ranging from 8–16 for common metal ions (e.g., Ca²⁺, Mg²⁺, Fe³⁺, Cu²⁺).
- The stability of these complexes depends on:
- pH: Complexes are more stable in alkaline conditions.
- Metal Ion Type: Transition metals and heavy metals form more stable complexes than alkali and alkaline earth metals.
C. Storage Stability
- Dry Form:
- EDTA·Na₄ is stable in its dry, crystalline form when stored in a cool, dry place away from moisture and strong acids or bases.
- Aqueous Solutions:
- Aqueous solutions of EDTA·Na₄ are stable for extended periods if stored in sealed containers to prevent contamination or evaporation.
3. Factors Affecting Solubility and Stability
| Factor | Effect on Solubility | Effect on Stability |
|---|---|---|
| pH | High solubility in alkaline conditions | Stable in alkaline pH, degrades in acidic pH |
| Temperature | Solubility increases with temperature | Stable at moderate temperatures |
| Oxidizing Agents | No direct effect on solubility | Degrades under strong oxidizing conditions |
| Metal Ions | Forms soluble complexes with metal ions | Enhances stability of metal complexes |
Summary
- Solubility: EDTA·Na₄ is highly soluble in water (> 100 g/100 mL) and insoluble in organic solvents.
- Stability:
- Chemically stable in alkaline conditions (pH ~ 11–12).
- Forms stable complexes with metal ions.
- Degrades in acidic conditions or under strong oxidizing agents.
- Stable in dry form and aqueous solutions when stored properly.
These properties make EDTA·Na₄ a versatile and reliable chelating agent for industrial, laboratory, and commercial applications.