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Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 99b

The solubility of CaCO3 is pH dependent. (b) Use the Kb expression for the CO32 - ion to determine the equilibrium constant for the reaction CaCO31s2 + H2O1l2 ΔCa2 + 1aq2 + HCO3-1aq2 + OH-1aq2

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is an equilibrium constant that applies to the solubility of sparingly soluble ionic compounds. It represents the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced equation. For calcium carbonate (CaCO3), Ksp can be used to understand how its solubility changes with pH, as the formation of bicarbonate and carbonate ions affects the equilibrium.
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Solubility Product Constant

Base Ionization Constant (Kb)

The base ionization constant (Kb) is a measure of the strength of a base in solution, indicating how well it can accept protons (H+) from water. For the carbonate ion (CO32-), Kb can be used to derive the equilibrium constant for its reaction with water, producing bicarbonate (HCO3-) and hydroxide ions (OH-). This relationship is crucial for understanding the pH dependence of CaCO3 solubility.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. In the context of CaCO3 solubility, changes in pH (which affect the concentration of H+ ions) will shift the equilibrium position, influencing the solubility of CaCO3 and the formation of its ions in solution.
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Related Practice
Textbook Question

Suppose you want to do a physiological experiment that calls for a pH 6.50 buffer. You find that the organism with which you are working is not sensitive to the weak acid H2A 1Ka1 = 2 * 10-2; Ka2 = 5.0 * 10-72 or its sodium salts. You have available a 1.0 M solution of this acid and a 1.0 M solution of NaOH. How much of the NaOH solution should be added to 1.0 L of the acid to give a buffer at pH 6.50? (Ignore any volume change.)

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Textbook Question

Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?

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Textbook Question

For each pair of compounds, use Ksp values to determine which has the greater molar solubility: (b) PbCO3 or BaCrO4.

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Textbook Question

Tooth enamel is composed of hydroxyapatite, whose simplest formula is Ca51PO423OH, and whose corresponding Ksp = 6.8 * 10-27. As discussed in the Chemistry and Life box on page 746, fluoride in fluorinated water or in toothpaste reacts with hydroxyapatite to form fluoroapatite, Ca51PO423F, whose Ksp = 1.0 * 10-60. (a) Write the expression for the solubility-constant for hydroxyapatite and for fluoroapatite.

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Textbook Question

Calculate the solubility of Mg1OH22 in 0.50 M NH4Cl.

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Textbook Question

The solubility-product constant for barium permanganate, Ba1MnO422, is 2.5 * 10-10. Assume that solid Ba1MnO422 is in equilibrium with a solution of KMnO4. What concentration of KMnO4 is required to establish a concentration of 2.0 * 10-8 M for the Ba2 + ion in solution?

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