Sarthaks Test
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AgNO3 is added to a solution that is 0.10 M in NaCl and 0.010 M K2CrO4. Assume no dilution caused by the addition of AgNO3. Given the Ksp values below:

Ksp for AgCl = 1.6x10–10 

Ksp for Ag2CrO4 = 9.0x10–12

a) Which precipitates first, AgCl or Ag2CrO4? Calculate the [Ag+ ] when precipitation first begins.

(b) What is the [Cl ] when Ag2CrO4 first begins to precipitate?

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(a) Since the solution stoichiometry for both these compounds are not the same, it would not be appropriate to relate Ksp and molar solubility.

To determine which ion precipitates first, we must calculate the cation concentration required for each precipitation. The lower value required for precipitation would indicate the ion that would precipitate first.

[Ag+ ] required for AgCl precipitation: 

[Ag+ ] required for Ag2CrO4 precipitation:

The precipitation occurs for the salt which requires the smallest [Ag+ ] at equilibrium. Therefore AgCl precipitates first at a [Ag+ ] of 1.6 x 10–9 M

(b) Calculations above show that in order of Ag2CrO4 to precipitate, the [Ag+ ] must equal 3.0x10–5 M. Therefore,

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