   Chapter 16, Problem 35E

Chapter
Section
Textbook Problem

# For each of the following pairs of solids, determine which solid has the smallest molar solubility.a. CaF2(s), Ksp = 4.0 × 10−11, or BaF2(s), Ksp = 2.4 × 10−5b. Ca3(PO4)2(s), Ksp = 1.3 × 10−32, or FePO4(s), Ksp = 1.0 × 10−22

(a)

Interpretation Introduction

Interpretation: The solubility product of each pair of solids is given. The solid that has the smallest molar solubility is to be identified from each given pairs.

Concept introduction: Solubility is defined as the maximum amount of solute that can dissolve at a certain amount of solvent at certain temperature. The solubility product, Ksp is the equilibrium constant that is applied when salt partially dissolve in a solvent. The solubility product of dissociation of AxBy is calculated as,

Ksp=[A]x[B]y

Explanation

Explanation

To identify: The solid that has the smallest molar solubility from CaF2 and BaF2 .

The solubility of CaF2 is 2.1×104mol/L_ .

Given

Solubility product of CaF2 is 4.0×1011 .

Since, solid CaF2 is placed in contact with water. Therefore, compound present before the reaction is CaF2 and H2O . The dissociation reaction of CaF2 is,

CaF2(s)Ca2+(aq)+2F(aq)

Since, CaF2 does not dissolved initially, hence,

[Ca2+]initial=[F]initial=0

The solubility of CaF2 can be calculated from the concentration of ions at equilibrium.

It is assumed that smol/L of solid is dissolved to reach the equilibrium. The meaning of 1:2 stoichiometry of salt is,

smol/LCaF2smol/LCa2++2smol/LF

Make the ICE table for the dissociation reaction of CaF2 .

CaF2(s)Ca2+(aq)2F(aq)Initial(M):00Chang(M):s2sEquilibrium(M):s2s

Formula

The solubility product of CaF2 is calculated as,

Ksp=[Ca2+][F]2=(s)(2s)2

Where,

• Ksp is solubility product.
• [Ca2+] is concentration of Ca2+ .
• [F] is concentration of F .
• s is the solubility.

Substitute the values of Ksp in the above expression.

Ksp=(s)(2s)24.0×1011=4s3s=2.1×104mol/L_

The solubility of BaF2 is 1.8×102mol/L_ .

Given

Solubility product of BaF2 is 2

(b)

Interpretation Introduction

Interpretation: The solubility product of each pair of solids is given. The solid that has the smallest molar solubility is to be identified from each given pairs.

Concept introduction: Solubility is defined as the maximum amount of solute that can dissolve at a certain amount of solvent at certain temperature. The solubility product, Ksp is the equilibrium constant that is applied when salt partially dissolve in a solvent. The solubility product of dissociation of AxBy is calculated as,

Ksp=[A]x[B]y

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