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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 27

Separate samples of a solution of an unknown salt are treated with dilute solutions of HBr, H2SO4, and NaOH. A precipitate forms in all three cases. Which of the following cations could be present in the unknown salt solution: K+, Pb2+, Ba2+?

Verified step by step guidance
1
Identify the possible reactions that could occur when the unknown salt solution is treated with HBr, H2SO4, and NaOH.
Consider the solubility rules for common ionic compounds to determine which cations form precipitates with the given anions.
For HBr, check which cations form insoluble bromides. Pb^{2+} forms PbBr2, which is insoluble.
For H2SO4, check which cations form insoluble sulfates. Ba^{2+} forms BaSO4, which is insoluble.
For NaOH, check which cations form insoluble hydroxides. Pb^{2+} forms Pb(OH)2, which is insoluble.

Key Concepts

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

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble compound, known as a precipitate. The formation of a precipitate indicates that the ions in solution have combined to form a compound that is not soluble in water. Understanding the solubility rules helps predict whether a precipitate will form when different reagents are added to a solution.
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Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. In this context, HBr and H2SO4 are strong acids that can react with bases or certain metal cations to form soluble or insoluble salts. The ability of a cation to form a precipitate with an acid indicates its reactivity and solubility characteristics, which are essential for identifying the unknown salt.
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Solubility Rules

Solubility rules are guidelines that predict the solubility of various ionic compounds in water. For example, most sulfates are soluble, except for those of barium, lead, and calcium, while hydroxides are generally insoluble except for alkali metals and some alkaline earth metals. These rules are crucial for determining which cations (K+, Pb2+, Ba2+) could be present in the unknown salt based on the observed precipitate formation.
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Related Practice
Textbook Question

Which ions remain in solution, unreacted, after each of the following pairs of solutions is mixed? (c) ammonium phosphate and calcium chloride

Textbook Question

Write balanced net ionic equations for the reactions that occur in each of the following cases. Identify the spectator ion or ions in each reaction. a. Cr2(SO4)3(π‘Žπ‘ž)+(NH4)2CO3(π‘Žπ‘ž)⟢

Textbook Question

Write balanced net ionic equations for the reactions that occur in each of the following cases. Identify the spectator ion or ions in each reaction. c. Fe(NO3)2(π‘Žπ‘ž)+KOH(π‘Žπ‘ž)⟢

Textbook Question

Separate samples of a solution of an unknown ionic compound are treated with dilute AgNO3, Pb1NO322, and BaCl2. Precipitates form in all three cases. Which of the following could be the anion of the unknown salt: Br-, CO32-, NO3-?

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Textbook Question

You know that an unlabeled bottle contains an aqueous solution of one of the following: AgNO3,CaCl2, or Al2(SO4)3. You take a portion of the solution and add an aqueous solution of Ba(NO3)2 to it, and observe that a white solid precipitates Then you take another portion of the unlabeled solution and add an aqueous solution of NaCl to it; nothing appears to happen. What is the most likely identity of the solution in the unlabeled bottle: silver nitrate, calcium chloride, aluminum sulfate?

Textbook Question

Three solutions are mixed together to form a single solution; in the final solution, there are 0.2 mol Pb1CH3COO)2, 0.1 mol Na2S, and 0.1 mol CaCl2 present. What solid(s) will precipitate?

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