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Solubility Equilibria: Flashcards

Revise Ksp expressions, molar solubility, the common-ion effect and predicting precipitates.

10 cardsIntermediate

10 cards

  1. Question
    What is Ksp?
    Answer

    The solubility product: the equilibrium constant for a slightly soluble salt dissolving, the product of its ion concentrations in a saturated solution.

  2. Question
    Write the Ksp expression for CaF₂.
    Answer

    Ksp=[CaX2+][FX−]2K_\text{sp} = [\ce{Ca^2+}][\ce{F-}]^2

  3. Question
    Why is the solid left out of the Ksp expression?
    Answer

    The concentration of a pure solid is constant.

  4. Question
    How is Ksp related to the molar solubility s for a 1 : 1 salt such as AgCl?
    Answer

    Ksp=s2K_\text{sp} = s^2

  5. Question
    How is Ksp related to s for a 1 : 2 salt such as CaF₂?
    Answer

    Ksp=s(2s)2=4s3K_\text{sp} = s(2s)^2 = 4s^3

  6. Question
    What is the common-ion effect?
    Answer

    A salt is less soluble in a solution that already contains one of its ions, because the equilibrium shifts to the left.

  7. Question
    When does a precipitate form?
    Answer

    When the ion product Q is greater than Ksp.

  8. Question
    Calculate the molar solubility of AgCl (Ksp = 1.8 × 10⁻¹⁰).
    Answer

    s=1.8×10−10=1.3×10−5s = \sqrt{1.8 \times 10^{-10}} = 1.3 \times 10^{-5} mol/L

  9. Question
    Why can't you always compare Ksp values directly to rank solubility?
    Answer

    Salts with different ion ratios have different Ksp formulas (s² vs 4s³); compare molar solubilities instead.

  10. Question
    What must you do to concentrations when two solutions are mixed before calculating Q?
    Answer

    Recalculate them for the new total volume (dilution).