* AgCl is a sparingly soluble salt. It has a very low solubility product constant (Ksp), meaning it doesn't dissolve readily in water.
* Thiosulfate ions (S2O3^2-) are good ligands. They can form coordinate bonds with silver ions (Ag+).
* Complex ion formation: When AgCl is added to a sodium thiosulfate solution, the following reaction occurs:
AgCl(s) + 2S2O3^2-(aq) ⇌ [Ag(S2O3)2]^3-(aq) + Cl-(aq)
This reaction results in the formation of a stable complex ion, [Ag(S2O3)2]^3-, called the dicyanoargentate(I) ion. This complex ion is soluble in water, effectively removing silver ions from solution and driving the equilibrium to the right, causing more AgCl to dissolve.
In summary:
The solubility of AgCl in sodium thiosulfate is not due to direct dissolving of AgCl in the thiosulfate solution. Instead, it's driven by the formation of a soluble complex ion, [Ag(S2O3)2]^3-, which removes silver ions from solution, allowing more AgCl to dissolve. This process is known as complexation.
