Question

Silver chloride has a molar solubility in water of 1.0 * 10^-5 mol/l. if silver chloride is dissolved in deionized water, what will the equilibrium concentrations of Ag+ and Cl- be and what is the value of Ksp for silver chloride? What chemicals could you add to the silver chloride solution to reduce its molar solubility?

Answer 1

Silver chloride (AgCl) dissolves as follows in water,

It is given that AgCl has a molar solubility of .

Hence, only of AgCl dissociates in 1 L of solution.

From the balanced equation above, 1 mol of AgCl dissolves to form 1 mol of Ag⁺ cation and 1 mol of Cl^- anion.

Hence, the equilibrium concentrations of the ions will be equal to the number of moles of AgCl dissolved per litre.

Hence,

Now, the equilibrium constant K_sp of the dissolution equation can be expressed as

Hence, the value of K_sp for AgCl is .

Now, if we add a strong electrolyte which contains a common ion with AgCl i.e. an electrolyte that has a Cl^- or Ag⁺, the equilibrium concentration of that anion or cation will increase. Since Ksp value of AgCl is constant, the equilibrium concentration of the other ion will decrease and hence the solubility will decrease.

Hence, the examples of chemicals that contains a common ion and will reduce the solubility of AgCl are

In fact any strong electrolyte that dissociates to form either of Ag⁺ or Cl^- in solution will decrease the solubility of AgCl. This decrease in solubility is also called common ion effect.