why AgCl is sparingly soluble in water but dissolves completely in NH4OH.
Answers
But AgCl dissolves in NH₄OH due to the formation of coordinate complex with it.
AgCl+2NH₃ -->[Ag(NH₃)₂]⁺ + Cl⁻
Answer:
Silver chloride (AgCl) do not dissolve in water. The forces holding the solid AgCl lattice together are too strong to be overcome by the forces favoring the formation of the hydrated ions, Ag+(aq) and Cl-(aq).
For an ionic compounds to dissolve, the Mandelung energy between ions in the lattice must be overcome. In a solution in which the ions are separated by molecules of solvent with a high dielectric constant, the attractive forces will be considerably less.
AgCl(s) ⇌ Ag+(aq) + Cl−(aq)
However, there is a limit to how much salt can be dissolved in a given volume of water. This amount is given by the solubility product, Ksp. This value depends on the type of salt (AgCl vs. NaCl, for example), temperature, and the common ion effect.
Ksp = [Ag+] × [Cl−] (definition of solubility product)
Ksp = 1.8 × 10^−10 (from a table of solubility products)
[Ag+] = [Cl−], in the absence of other silver or chloride salts,
[Ag+]2 = 1.8 × 10^−10
[Ag+] = 1.34 × 10^−5.
The result: 1 liter of water can dissolve 1.34 × 10^−5 moles of AgCl(s) at room temperature. Compared with other types of salts, AgCl is poorly soluble in water.
. Therefore, we turn to another useful trick for dissolving precipitates: we take advantage of the tendency of transition metal ions such as Ag+ to form water-soluble complex ions with ammonia, NH3. Here the ammonia uses the lone pair of electrons of the N atom to form a bond with the Ag+ ion.
[H3N : → Ag+ ← : NH3] , a water-soluble complex ion
When a large enough concentration of NH3 is added to an insoluble precipitate of AgCl, the ammonia binds to the Ag+ ion and forms the complex ion. The net result is that the AgCl dissolves.
AgCl(s) + 2 NH3(aq) → [Ag(NH3)2]+(aq) + Cl–(aq).
The formation of the complex [Ag(NH3)2]+ ion makes it behave like ionic therefore making it soluble.