   Chapter 17, Problem 102IL

Chapter
Section
Textbook Problem

Each pair of ions below is found together in aqueous solution. Using the table of solubility product constants in Appendix J, devise a way to separate these ions by adding a reagent to precipitate one of the ions as an insoluble salt and leave the other in solution. (a) Cu2+ and Ag+ (b) A13+ and Fe3+

(a)

Interpretation Introduction

Interpretation:

One reagent to separate the given ion pairs by precipitating one as insoluble salt and leaving other in the solution has to be suggested.

Concept introduction:

The solubility of a salt is defined as the maximum amount of salt that can be dissolved in definite amount of solvent. It is expressed in moles per liter or grams per liter. Solubility in terms of moles per liter is called molar solubility and is defined as the number of moles of solute (salt) dissolved in per liter of solution.

Solubility product constant Ksp is an equilibrium constant and is defined as the product of the equilibrium concentration of the ions of the salt raised to the power of their coefficients in the balanced chemical equation.

The expression for Ksp of a salt is given as,

AxBy(s)xAy+(aq)+yBx(aq)Ksp=[Ay+]x[Bx]y

When in the solution more than one insoluble salt having one common ion is present than the one which requires less amount of the common ion to exceed its solubility product value and precipitate will precipitate out first from the solution. This is known as preferential precipitation.

Explanation

Refer to the Appendix J in the textbook for the value of Ksp.

Solubility product constant Ksp for AgCl is 1.8×1010 which is very small compared to Ksp for CuCl2 is 1

(b)

Interpretation Introduction

Interpretation:

One reagent to separate the given ion pairs by precipitating one as insoluble salt and leaving other in the solution has to be suggested.

Concept introduction:

The solubility of a salt is defined as the maximum amount of salt that can be dissolved in definite amount of solvent. It is expressed in moles per liter or grams per liter. Solubility in terms of moles per liter is called molar solubility and is defined as the number of moles of solute (salt) dissolved in per liter of solution.

Solubility product constant Ksp is an equilibrium constant and is defined as the product of the equilibrium concentration of the ions of the salt raised to the power of their coefficients in the balanced chemical equation.

The expression for Ksp of a salt is given as,

AxBy(s)xAy+(aq)+yBx(aq)Ksp=[Ay+]x[Bx]y

When in the solution more than one insoluble salt having one common ion is present than the one which requires less amount of the common ion to exceed its solubility product value and precipitate will precipitate out first from the solution. This is known as preferential precipitation.

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