Why Does the Common Ion Effect Increase Ksp for AgCl in the Presence of Cl-?

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In summary, the conversation discusses comparing the Ksp values of pure water solutions and those with an ion already present. An example using AgCl and NaCl is given, with a question about the Ksp with .01M of Cl- already present. The calculated answer is 1.77x10^-8, which is larger than the pure water Ksp of 1.77x10^-10. This raises questions about the dissociation of AgCl with the presence of an extra ion.
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I'm working Ksp problems comparing pure water solutions w/ those with an ion already present in solution. Example: AgCl and NaCl both in solution.

The pure water Ksp for AgCl is given as 1.77x10^-10. The question is what the Ksp would be with .01M of Cl- already present. After working the problem, I get an answer (verified as correct) as: 1.77x10^-8. This makes mathematic sense, but it doesn't intuitively make sense to me. The Ksp is larger (10^-8) with the extra ion than for pure water (10^-10)? Doesn't this indicate that AgCl dissociates MORE with .01M Cl- already present? How?
 
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1.77x10-8 is not Ksp, but concentration of Ag+ in the solution. Ksp is constant (as long as temperature doesn't change).
 
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FAQ: Why Does the Common Ion Effect Increase Ksp for AgCl in the Presence of Cl-?

What is the common ion effect?

The common ion effect is a phenomenon in chemistry where the presence of a common ion in a solution decreases the solubility of a slightly soluble salt. This occurs because the common ion reduces the activity of the ions in the solution, pushing the equilibrium towards the solid form of the salt.

How does the common ion effect affect equilibrium?

The common ion effect affects equilibrium by shifting the equilibrium towards the direction that reduces the solubility of the salt. This is because the common ion decreases the activity of the ions in the solution, making it more difficult for the salt to dissolve. This results in a decrease in the concentration of ions in the solution, which shifts the equilibrium towards the solid form of the salt.

What are some examples of common ion effect in everyday life?

Some examples of common ion effect in everyday life include the addition of table salt (NaCl) to a saturated solution of sodium chloride, which causes the precipitation of salt; the addition of ammonium chloride (NH4Cl) to a solution of ammonia (NH3) and water, which causes the solution to become more acidic due to the common ion effect; and the addition of sodium fluoride (NaF) to a solution of hydrofluoric acid (HF), which decreases the strength of the acid due to the common ion effect.

How can the common ion effect be minimized or eliminated?

The common ion effect can be minimized or eliminated by diluting the solution or by using a different solvent that does not contain the common ion. Another method is to add a salt that contains an ion that does not participate in the equilibrium, such as an inert ion. This will decrease the concentration of the common ion and shift the equilibrium towards the desired direction.

How does the common ion effect impact solubility calculations?

The common ion effect must be taken into account when calculating the solubility of a slightly soluble salt in the presence of a common ion. The solubility can be calculated by using the solubility product constant (Ksp) and the concentration of the common ion in the solution. The presence of a common ion will decrease the solubility of the salt, resulting in a smaller value for the solubility.

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