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Ch.17 - Additional Aspects of Aqueous Equilibria
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.17 - Additional Aspects of Aqueous EquilibriaProblem 79a,b
Chapter 17, Problem 79a,b

In the course of various qualitative analysis procedures, the following mixtures are encountered: (a) Zn2+ and Cd2+. (b) Cr(OH)3 and Fe(OH)3 Suggest how each mixture might be separated.

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Identify the chemical properties of Zn^{2+} and Cd^{2+} ions, such as their solubility in different reagents.
Consider using a reagent that forms a precipitate with one ion but not the other. For example, sulfide ions (S^{2-}) can be used to precipitate CdS, which is insoluble, while ZnS is more soluble in acidic conditions.
Add a dilute acid to the mixture to ensure that ZnS remains dissolved while CdS precipitates out.
Filter the mixture to separate the solid CdS from the solution containing Zn^{2+}.
Wash and dry the precipitate to obtain pure CdS, and the remaining solution will contain Zn^{2+} ions.

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Key Concepts

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

Solubility and Precipitation Reactions

Solubility refers to the ability of a substance to dissolve in a solvent, while precipitation reactions occur when two soluble salts react to form an insoluble compound. Understanding these concepts is crucial for separating ions in a mixture, as selective precipitation can be used to isolate specific ions based on their differing solubilities.
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Complex Ion Formation

Complex ion formation involves the interaction of metal ions with ligands to form a stable complex. This concept is essential for separating metal ions like Zn<sup>2+</sup> and Cd<sup>2+</sup>, as specific ligands can selectively bind to one metal ion over the other, allowing for their separation through techniques such as extraction or chromatography.
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Ion Selectivity and Chromatography

Ion selectivity refers to the ability to preferentially separate ions based on their chemical properties. Chromatography is a technique that exploits these differences, allowing for the separation of Zn<sup>2+</sup> and Cd<sup>2+</sup> by passing the mixture through a medium that interacts differently with each ion, thus achieving separation based on their affinities.
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Related Practice
Textbook Question

Suggest how the cations in each of the following solution mixtures can be separated: (c) Pb2 + and Al3 +.

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Textbook Question

(b) What is the most significant difference between the sulfides precipitated in group 2 and those precipitated in group 3?

Textbook Question

In the course of various qualitative analysis procedures, the following mixtures are encountered: (c) Mg2+ and K+ (d) Ag+ and Mn2+. Suggest how each mixture might be separated.

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Textbook Question

A solution containing several metal ions is treated with dilute HCl; no precipitate forms. The pH is adjusted to about 1, and H2S is bubbled through. Again, no precipitate forms. The pH of the solution is then adjusted to about 8. Again, H2S is bubbled through. This time a precipitate forms. The filtrate from this solution is treated with (NH4)2HPO4. No precipitate forms. Which of these metal cations are either possibly present or definitely absent: Al3+, Na+, Ag+, Mg2+?

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