Textbook Question
Determine the minimum concentration of the precipitating agent on the right to cause precipitation of the cation from the solution on the left. a. 0.035 M Ba(NO3)2; NaF
Ch.18 - Aqueous Ionic Equilibrium
Chapter 18, Problem 106b
Determine the minimum concentration of the precipitating agent on the right to cause precipitation of the cation from the solution on the left. b. 0.085 M CaI2; K2SO4
Verified step by step guidance1
Identify the ions involved in the precipitation reaction. In this case, calcium ions (Ca^{2+}) from CaI_2 and sulfate ions (SO_4^{2-}) from K_2SO_4.
Write the balanced chemical equation for the precipitation reaction: Ca^{2+} (aq) + SO_4^{2-} (aq) \rightarrow CaSO_4 (s).
Determine the solubility product constant (K_{sp}) for the precipitate, CaSO_4. This value is typically found in a chemistry reference or textbook.
Use the expression for the solubility product: K_{sp} = [Ca^{2+}][SO_4^{2-}].
Rearrange the expression to solve for the minimum concentration of sulfate ions needed to cause precipitation: [SO_4^{2-}] = \frac{K_{sp}}{[Ca^{2+}]}. Substitute the given concentration of Ca^{2+} (0.085 M) and the K_{sp} value to find the minimum [SO_4^{2-}].
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Precipitation Reaction
A precipitation reaction occurs when two soluble salts react in solution to form an insoluble solid, known as a precipitate. This process is driven by the formation of a compound that has low solubility in the solvent, leading to the separation of the solid from the liquid phase. Understanding the solubility product constant (Ksp) is crucial, as it helps predict whether a precipitate will form based on the concentrations of the reactants.
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Selective Precipitation
Solubility Product Constant (Ksp)
The solubility product constant (Ksp) is an equilibrium constant that quantifies the solubility of a sparingly soluble ionic compound. It is defined as the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced equation. For a precipitation reaction to occur, the product of the ion concentrations must exceed the Ksp value, indicating that the solution is supersaturated and a precipitate will form.
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Concentration and Stoichiometry
Concentration refers to the amount of a substance in a given volume of solution, typically expressed in molarity (M). In precipitation reactions, stoichiometry is used to relate the concentrations of reactants and products based on their molar ratios in the balanced chemical equation. Calculating the minimum concentration of the precipitating agent requires understanding these relationships to ensure that the conditions for precipitation are met.
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Related Practice
Textbook Question
Determine the minimum concentration of the precipitating agent on the right to cause precipitation of the cation from the solution on the left. c. 0.0018 M AgNO3; RbCl
Textbook Question
A solution is 0.010 M in Ba2+ and 0.020 M in Ca2+. a. If sodium sulfate is used to selectively precipitate one of the cations while leaving the other cation in solution, which cation will precipitate first? What minimum concentration of Na2SO4 will trigger the precipitation of the cation that precipitates first?
Textbook Question
A solution is 0.010 M in Ba2+ and 0.020 M in Ca2+. b. What is the remaining concentration of the cation that precipitates first, when the other cation begins to precipitate?