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Ch.4 - Reactions in Aqueous Solution
All textbooksBrown 14th EditionCh.4 - Reactions in Aqueous SolutionProblem 36
Chapter 4, Problem 36

An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of NaCl of the same concentration. Which of the following substances could the unknown be: KOH, NH3, HNO3, KClO2, H3PO3, CH3COCH3 (acetone)?

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1
Identify the nature of the solution: The solution is acidic, which means the unknown solute must be an acid.
Consider the conductivity: The solution is weakly conducting, indicating that the solute is a weak acid or a weak base, as strong acids and bases fully dissociate and conduct electricity well.
Evaluate the given substances: KOH is a strong base, NH3 is a weak base, HNO3 is a strong acid, KClO2 is a salt, H3PO3 is a weak acid, and CH3COCH3 (acetone) is a neutral compound.
Eliminate options: Since the solution is acidic, eliminate KOH and NH3. Since the solution is weakly conducting, eliminate HNO3, as it is a strong acid.
Determine the possible substance: The remaining options are H3PO3, which is a weak acid, and CH3COCH3, which is neutral. Since the solution is acidic, the unknown solute is likely H3PO3.

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Key Concepts

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

Acidity and pH

Acidity refers to the concentration of hydrogen ions (H+) in a solution, which determines its pH level. A solution with a pH less than 7 is considered acidic. In this context, the unknown solute must produce H+ ions when dissolved in water, indicating it is an acid.
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pH of Strong Acids and Bases

Electrical Conductivity of Solutions

The electrical conductivity of a solution is influenced by the presence of ions, which carry electric charge. Strong electrolytes, like NaCl, dissociate completely into ions, leading to high conductivity. Weak electrolytes, such as weak acids or bases, only partially dissociate, resulting in lower conductivity, which is relevant for identifying the unknown solute.
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Solution Components

Classification of Solutes

Solutes can be classified as strong acids, weak acids, strong bases, weak bases, or neutral substances based on their behavior in solution. Strong acids fully dissociate in water, while weak acids do not. Understanding this classification helps in determining which of the given substances could be the unknown solute based on its acidic nature and conductivity.
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Related Practice
Textbook Question

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (b) acetonitrile, CH3CN

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Textbook Question

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (c) NaClO4

386
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Textbook Question

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (d) Ba1OH22.

949
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Textbook Question

Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) HF (b) C6H5COOH (benzoic acid) (c) C6H6 (benzene) (d) CoCl3 (e) AgNO3.

755
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Textbook Question

Complete and balance the following molecular equations, and then write the net ionic equation for each:

(a) HBr(aq) + Ca(OH)2(aq) →

(b) Cu(OH)2(s) + HClO4(aq) →

(c) Al(OH)3(s) + HNO3(aq) →

832
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