Silver iodide (AgI) is insoluble in water. 1 It forms a yellowish precipitate when added to water due to the weak electrostatic forces between the silver cations (Ag+) and iodide anions (I-) which are not strong enough to overcome the hydration energies of water molecules.
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Why is AgI insoluble in water?
AgI (silver iodide) is insoluble in water due to the large difference in electronegativity between silver (Ag) and iodine (I) atoms. 2 This creates a strong ionic bond between Ag and I, resulting in a crystal lattice structure that does not easily dissolve in water.
Silver iodide (AgI) is composed of silver cations (Ag+) and iodide anions (I-) held together by ionic bonds. Silver is a metal with low electronegativity, while iodine is a nonmetal with high electronegativity. 3
The large difference in electronegativity between the two elements creates a strong attraction between Ag+ and I-. The ionic bond formed between them is highly stable and requires a significant amount of energy to break.
When AgI is placed in water, the water molecules form hydration shells around the silver and iodide ions. However, the attraction between the ions and the water molecules is not strong enough to overcome the strong ionic bond within the crystal lattice. As a result, the AgI crystals do not dissociate into individual ions and remain intact, making AgI insoluble in water.
The insolubility of AgI in water has practical applications, such as in cloud seeding to induce rainfall. 4 AgI particles are dispersed in clouds, where they serve as nuclei for water droplet formation.
The insolubility of AgI ensures that the particles remain intact and effective in promoting cloud condensation and precipitation.
Further reading
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References
- P. (n.d.). Silver Iodide. Silver Iodide | AgI | CID 24563 – PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/24563
- Is AgI Soluble or Insoluble in Water? (2020, April 2). YouTube. https://www.youtube.com/watch?v=d9tOmmKJCWI
- Tantardini, C., & Oganov, A. R. (2021, April 7). Thermochemical electronegativities of the elements. Nature Communications, 12(1). https://doi.org/10.1038/s41467-021-22429-0
- What is Cloud Seeding? (n.d.). DRI. https://www.dri.edu/cloud-seeding-program/what-is-cloud-seeding/