Question

An aqueous solution that 2.10M in AgNO3 is slowly added from a buret to an aqueous solution that is 1.20

Answer 1

Concentration of AgNO₃ = 2.10M

[Cl^-] = 1.2X10^-2M

[I^-] = 0.25M

A).   Ksp for AgI = about 10^-17
Ksp for AgCl = about 10^-10

As the solubility product of AgI is low, therefore, AgI will precipitate first.

B). The [Ag⁺] when AgCl just starts to precipitate:

[Ag⁺] = Ksp/ [Cl^-] = 10^-10/0.012

= 8.33X10^-9M

Now, the concentration of I^- at this point [I^-] = Ksp/ [Ag⁺]

= 10^-17/ 8.33X10^-9

= 1.20X10^-9 M

C). Yes,  the separation of Cl- and I- is feasible by fractional precipitation in this solution.

• Fractional precipitation tests for certain ions using color change, solid formation, and other visible changes.

• Chlorides, bromides, and iodides can be detected by adding a small amount of silver nitrate solution.

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Prepare a solution of the unknown salt using distilled water and add a small amount of silver nitrate (AgNO₃)

solution. If a white precipitate forms, the salt is either a chloride or a carbonate. Why?

If there is chlorine in the solution, the balanced reaction would be:

Cl^-   +   Ag⁺   +   NO^3-      AgCl + NO^3-

Silver chloride (AgCl) is not soluble and forms a white precipitate.

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