Chemistry Equilibrium MDCAT 2015
PMDC Verified Question 94 of 102
Which one of the following is the correct representation for \( K_{sp} \)?

$$ \text{AgCl} \rightleftharpoons \text{Ag}^+ + \text{Cl}^- $$
A
\( K_{sp} = \frac{[\text{AgCl}]}{[\text{Ag}^+][\text{Cl}^-]} \)
B
\( K_{sp} = \frac{[\text{Ag}^+][\text{Cl}^-]}{[\text{AgCl}]} \)
C
\( K_{sp} = [\text{Ag}^+][\text{Cl}^-] \)
D
\( K_{sp} = [\text{AgCl}] \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( K_{sp} = [\text{Ag}^+][\text{Cl}^-] \)
Concept:

The solubility product constant (\( K_{sp} \)) is the equilibrium constant for a solid substance dissolving in an aqueous solution, representing the product of dissolved ion concentrations.

Formula:

$$ K_{sp} = [\text{Cation}]^x [\text{Anion}]^y $$

Solution:

  • For the dissolution of \( \text{AgCl} \), the equilibrium expression is initially \( K_c = \frac{[\text{Ag}^+][\text{Cl}^-]}{[\text{AgCl}]} \).


  • Because \( \text{AgCl} \) is a pure solid, its concentration is constant and incorporated into the equilibrium constant.


  • This creates the new constant \( K_{sp} = [\text{Ag}^+][\text{Cl}^-] \).


Why other options are incorrect:

Solid reactants are never included in the denominator of a \( K_{sp} \) expression, eliminating A and B. Option D ignores the ions completely.

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