Chemistry 18.3

Solubility Equilibrium 18.3 Barium sulfate is ingested by a patient before X-ray images of the digestive tract are taken. Barium sulfate absorbs the X-rays, thereby producing light areas on the developed X-ray film. However, barium salts are usually toxic. You will learn why patients can ingest this poisonous substance without harm.

The Solubility Product Constant 18.3 The Solubility Product Constant The Solubility Product Constant What is the relationship between the solubility product constant (Ksp) and the solubility of a compound?

The Solubility Product Constant 18.3 The Solubility Product Constant The solubility product constant (Ksp), equals the product of the concentrations of the ions, each raised to a power equal to the coefficient of the ion in the dissociation equation. The smaller the numerical value of the solubility product constant, the lower the solubility of the compound.

e.g. Write the Ksp expression for: (i) AgCl (ii) BaSO4 (iii) PbCl2 (i) Ionization Equation: AgCl(s) Ag+(aq) + Cl-(aq) Ksp = [Ag+(aq)] [Cl-(aq) ] (ii) Ionization Equation: BaSO4(s) Ba2+(aq) + SO42-(aq) Ksp = [Ba2+(aq) ] [SO42-(aq)] (iii) Ionization Equation: PbCl2(s) Pb2+(aq) + 2 Cl-(aq) Ksp = [Pb2+(aq) ] [Cl-(aq)]2

The Solubility Product Constant 18.3 The Solubility Product Constant

The Solubility Product Constant 18.3 The Solubility Product Constant

The Solubility Product Constant 18.3 The Solubility Product Constant Silver chloride is slightly soluble in water. Silver chloride is slightly soluble in water. Predicting Would adding solid silver chloride to this test tube disturb the equilibrium?

The Solubility Product Constant 18.3 The Solubility Product Constant Scale, formed by the precipitation of slightly soluble salts, builds up around faucets. Scale, formed by the precipitation of slightly soluble salts, often builds up around kitchen and bathroom faucets. Applying Concepts Why are insoluble substances hard to remove?

18.3 The chromate ion is responsible for the brilliant yellow color of lead(II)chromate.

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for Sample Problem 18.3 Problem Solving 18.17 Solve Problem 17 with the help of an interactive guided tutorial.

More difficult problem : What will be the Pb2+ ion concentration and Cl- ion concentration in a saturated solution of lead (II) chloride? (Ksp = 1.7 x 10-5) Let’s try it on the board…

18.3 The Common Ion Effect The Common Ion Effect How can you predict whether precipitation will occur when two salt solutions are mixed? A precipitate of barium sulfate forms as barium nitrate (Ba(NO3)2) and sodium sulfate (Na2SO4) solutions are mixed. Applying Concepts What is the product of the concentrations of barium ion and sulfate ion after precipitation is complete?

18.3 The Common Ion Effect If the product of the concentrations of two ions in the mixture is greater than the Ksp of the compound formed from the ions, a precipitate will form.

Sample Problem (taken from p.565): Will a precipitate form when 0.500L of 0.002M Ba(NO3 )2 reacts with 0.500L of 0.008M Na2SO4? [Ksp (BaSO4) = 1.1 x 10-10] Let’s go to the board…

18.3 The Common Ion Effect A common ion is an ion that is found in both salts in a solution. The lowering of the solubility of an ionic compound as a result of the addition of a common ion is called the common ion effect. Example: adding lead (II) nitrate to an existing saturated solution of lead (II) chromate (see next page).

A saturated solution of lead(II) chromate is pale yellow. 18.3 The Common Ion Effect Lead(II) chromate is slightly soluble in water. a) A saturated solution of PbCrO4 is pale yellow. b) When a few drops of lead nitrate (Pb(NO3)2) are added to the solution, it becomes cloudy as more lead(II) chromate precipitates. Applying Concepts Explain what happened in b) by considering the addition of lead nitrate as a stress on the PbCrO4 equilibrium. When a few drops of lead nitrate are added to the solution, more lead(II) chromate precipitates. A saturated solution of lead(II) chromate is pale yellow.

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for Sample Problem 18.4 Problem Solving 18.19 Solve Problem 19 with the help of an interactive guided tutorial.

18.3 Section Quiz. 18.3.

18.3 Section Quiz. 1. What is the concentration of a saturated solution of silver sulfide? The Ksp of Ag2S is 8.0  10-51. 2.0  10-17M 8.9  10-26M 8.9  10-25M 2.0  1017M

18.3 Section Quiz. 2. Adding which of these solutions to a saturated solution of BaSO4 will cause the solubility of BaSO4 to decrease? I. BaCl2(aq) II. Na2SO4 (aq) (I) only (II) only (I) and (II) neither solution

18.3 Section Quiz. 3. The Ksp of AgBr is 5.0  10-13. When 7.1  10-6 mol/L solutions of NaBr(aq) and AgNO3(aq) are mixed, we would expect no precipitate to form. a definite precipitation reaction. no reaction. a saturated solution but no visible precipitation.

18.3 Section Quiz. 4. After the common ion effect causes a precipitate to form in a solution, the solution will no longer be saturated. the solution will again be saturated. the solution will be supersaturated. there will be no solute left in the solution.

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