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Ch.5 - Introduction to Solutions and Aqueous Solutions
Chapter 5, Problem 42

Determine whether each compound is soluble or insoluble. If the compound is soluble, list the ions present in solution. a. AgI b. Cu3(PO4)2 c. CoCO3 d. K3PO4

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Identify the solubility rules for each type of ion present in the compounds. For example, compounds containing alkali metal ions (like K+) and ammonium ion (NH4+) are generally soluble. Nitrates, acetates, and most perchlorates are soluble. Halides (except those of Ag+, Pb2+, and Hg2+) are soluble, and sulfates (except those of Ba2+, Sr2+, Pb2+, Ag+, and Ca2+) are soluble.
Apply the solubility rules to each compound: a. AgI contains the iodide ion (I-) and silver ion (Ag+). According to the solubility rules, iodides are generally soluble except when paired with silver, lead, or mercury. b. Cu3(PO4)2 contains the phosphate ion (PO4^3-) and copper ion (Cu2+). Phosphates are generally insoluble except when paired with ammonium or alkali metal ions. c. CoCO3 contains the carbonate ion (CO3^2-) and cobalt ion (Co2+). Carbonates are generally insoluble except when paired with ammonium or alkali metal ions. d. K3PO4 contains the phosphate ion (PO4^3-) and potassium ion (K+). Potassium is an alkali metal, making its salts generally soluble.
Determine the solubility of each compound based on the rules: a. AgI is insoluble due to the presence of Ag+ which makes iodides insoluble. b. Cu3(PO4)2 is insoluble because Cu2+ does not make phosphates soluble. c. CoCO3 is insoluble because Co2+ does not make carbonates soluble. d. K3PO4 is soluble because it contains the alkali metal ion K+.
List the ions present in solution for the soluble compounds: For K3PO4, which is soluble, the ions in solution are K+ and PO4^3-.
Summarize the solubility and ions in solution: AgI is insoluble, Cu3(PO4)2 is insoluble, CoCO3 is insoluble, and K3PO4 is soluble with K+ and PO4^3- ions in solution.

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Key Concepts

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

Solubility Rules

Solubility rules are guidelines that help predict whether a compound will dissolve in water. These rules state that certain ions, such as alkali metal ions and nitrate ions, generally form soluble compounds, while others, like silver and lead ions, often form insoluble compounds. Understanding these rules is essential for determining the solubility of various salts in aqueous solutions.
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Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between positively and negatively charged ions. When these compounds dissolve in water, they dissociate into their constituent ions, which can then interact with the solvent. Recognizing the ions present in a soluble compound is crucial for understanding the chemical behavior of the solution.
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Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble compound, known as a precipitate. This concept is important for identifying which compounds will remain dissolved and which will form solid particles when mixed. Understanding precipitation helps in predicting the outcome of mixing different ionic solutions.
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