Solubility Product — Ksp, precipitation conditions
Ionic Equilibrium
6
JEE Qs
8%
Hard
75
min
Master the relationship between Ksp, molar solubility, and the ionic product (Qsp), and meticulously apply stoichiometric principles to predict precipitation and solubility changes in various conditions.
🧮 Key Formulas
✅ Key Points for JEE
- 1Ksp is the solubility product constant, a measure of the extent to which a sparingly soluble ionic compound dissolves at a given temperature. It is a thermodynamic constant.
- 2The relationship between molar solubility (s) and Ksp is highly dependent on the stoichiometry of the salt; always correctly write the dissolution equilibrium expression.
- 3The common ion effect significantly decreases the solubility of a sparingly soluble salt by shifting its dissolution equilibrium towards the solid phase.
- 4Comparing the Ionic Product (Qsp) with Ksp allows for prediction of precipitation (Qsp > Ksp), dissolution (Qsp < Ksp), or saturation (Qsp = Ksp).
- 5The solubility of many sparingly soluble salts (e.g., hydroxides, carbonates, sulfides) is pH-dependent due to acid-base reactions of one of the constituent ions, which removes it from solution.
⚠️ Common Mistakes
- ✕Incorrectly relating molar solubility (s) to the concentration of individual ions based on stoichiometry (e.g., for CaF2, [F-] = 2s, not s).
- ✕Forgetting to raise ion concentrations to their stoichiometric coefficients in the Ksp or Qsp expression (e.g., Ksp = [A]^x [B]^y, not Ksp = x[A]y[B]).
- ✕Not accounting for dilution when mixing solutions, leading to incorrect initial ion concentrations for Qsp calculations.
- ✕Ignoring the common ion effect in problems where it's applicable, which leads to overestimation of solubility.
📝 Practice Questions
See allQ74.If 1 mM solution of ethylamine produces pH = 9, then the ionization constant (Kb) of ethylamine is 10−x . The value of x is ______ (nearest integer). [The degree of ionization of ethylamine can be neglected with respect to unity.]
Q61. Ksp for Cr(OH)3 is 1.6 × 10−30 . What is the molar solubility of this salt in water? (1) 1.8×10−30 (2) 5√1.8 × 10−30 27 × 10−30 (3) 4√1.6×10−3027 (4) 2√1.6
Q58.The molar solubility(s) of zirconium phosphate with molecular formula (Zr4+)3(PO3−4 )4 is given by relation : (1) Ksp 13 (2) Ksp 17 ( 9612 ) ( 6912 ) (3) Ksp 17 (4) Ksp 16 ( 8435 ) ( 5348 )
Q62.Which of the following happens when NH4OH is added gradually to the solution containing 1 M A2+ and 1MB3+ ions? Given : Ksp [A(OH)2] = 9 × 10−10 and Ksp [B(OH)3] = 27 × 10−18 at 298 K . (1) Both A(OH)2 and B(OH)3 do not show (2) A(OH)2 will precipitate before B(OH)3 precipitation with NH4OH (3) B(OH)3 will precipitate before A(OH)2 (4) A(OH)2 and B(OH)3 will precipitate together excess HCHO alkali−
Q68.pH of water is 7 at 25∘C. If water is heated to 80∘C., it's pH will : (1) Decrease (2) H+ concentration increases, OH− concentration decreases (3) Remains the same (4) Increase 2025 (23 Jan Shift 2) JEE Main Previous Year Paper
Q58.A weak acid HA has degree of dissociation x . Which option gives the correct expression of ( pH pKa )? (1) 0 (2) log(1 + 2x) (3) log ( 1−xx ) (4) log ( 1−xx )
NCERT Chapters
- Class 11 Chemistry Ch 7: Equilibrium