Question

You know that an unlabeled bottle contains an aqueous solution of one of the following: \(\mathrm{AgNO}_{3}, \mathrm{CaCl}_{2}\), or \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\). A friend suggests that you test a portion of the solution with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) and then with \(\mathrm{NaCl}\) solutions. According to your friend's logic, which of these chemical reactions could occur, thus helping you identify the solution in the bottle? (a) Barium sulfate could precipitate. (b) Silver chloride could precipitate. (c) Silver sulfate could precipitate. (d) More than one, but not all, of the reactions described in answers a-c could occur. (e) All three reactions described in answers a-c could occur.

Short answer

(d) More than one, but not all, of the reactions described could occur.

Step-by-step solution

Analyze Possible Reactions with Ba(NO₃)₂

When you add \( \mathrm{Ba(NO}_3)_2 \) to the unknown solution, potential precipitates could form if the anion in the solution reacts with \( \mathrm{Ba}^{2+} \) to form an insoluble compound. From the given options, \( \mathrm{BaSO}_4 \) forms a precipitate because \( \mathrm{BaSO}_4 \) is insoluble in water. Therefore, if the solution contains \( \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3 \), \( \mathrm{BaSO}_4 \) will form.

Analyze Possible Reactions with NaCl

Adding \( \mathrm{NaCl} \) to the unknown solution could produce a precipitate if \( \mathrm{AgNO}_3 \) is present, as \( \mathrm{AgCl} \) is insoluble in water. Therefore, if the solution contains \( \mathrm{AgNO}_3 \), \( \mathrm{AgCl} \) will form when \( \mathrm{NaCl} \) is added.

Evaluate Precipitate Formation

\( \mathrm{BaSO}_4 \) precipitate would indicate the presence of \( \mathrm{Al}_2(\mathrm{SO}_4)_3 \), while \( \mathrm{AgCl} \) precipitate would indicate the presence of \( \mathrm{AgNO}_3 \). There is no scenario where \( \mathrm{CaCl}_2 \) would produce either \( \mathrm{AgCl} \) or \( \mathrm{BaSO}_4 \) as these are both products of reactions from other specific solutions.

Confirm the Correct Answer

Based on the analysis, either \( \mathrm{BaSO}_4 \) or \( \mathrm{AgCl} \) could precipitate depending on whether \( \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3 \) or \( \mathrm{AgNO}_3 \) is in the solution, respectively. Since both precipitates can form independently from different solutions, the correct choice is (d) More than one, but not all, of the reactions described could occur.

Key concepts

Aqueous Solutions

An aqueous solution is a mixture where water acts as the solvent. In chemistry, solutions are essential because they allow substances to react more easily. This occurs because the solute, or the substance being dissolved, is uniformly dispersed within the solvent, making it available for reaction. One key characteristic of aqueous solutions is that they can be either an electrolyte or a nonelectrolyte. Electrolytes dissociate into ions, which allows them to conduct electricity. Common examples include salts like sodium chloride and acids like hydrochloric acid. Nonelectrolytes, on the other hand, do not dissociate into ions and therefore do not conduct electricity. Aqueous solutions are crucial in precipitation reactions, where soluble ions in separate solutions interact to form an insoluble solid. Understanding the properties of an aqueous solution can help predict the outcomes of various chemical reactions.

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in aqueous solution to form one or more insoluble products, known as precipitates. These reactions are a subdivision of double displacement reactions and are governed by the solubility rules of the resultant compounds. When a precipitate forms, it appears as a solid settling out of the liquid solution. This is significant because it can be used to identify the ions present in a solution. For example, in a lab experiment, mixing a solution containing barium nitrate with one containing sulfate ions often results in the formation of barium sulfate. Barium sulfate appears as a white solid and is evidence of a precipitation reaction. Such reactions can also be utilized in various applications, such as removing unwanted ions from water or serving analytical purposes in chemistry labs for detecting specific elements or compounds.

Solubility Rules

Solubility rules are guidelines that help predict whether an ionic compound will dissolve in water, forming an aqueous solution, or remain as a precipitate. These rules are essential for identifying the likelihood of precipitate formation during a chemical reaction. While there are many specific solubility rules, a few critical ones include:

• Most alkali metal salts and ammonium salts are soluble.
• Nitrates (NO₃⁻), acetates (CH₃COO⁻), and most perchlorates (ClO₄⁻) are soluble.
• Chlorides, bromides, and iodides are soluble, except when paired with Ag⁺, Pb²⁺, and Hg²⁺.
• Sulfates (SO₄²⁻) are generally soluble, but exceptions include Ba²⁺, Sr²⁺, and Pb²⁺.
• Most carbonates (CO₃²⁻), phosphates (PO₄³⁻), sulfides (S²⁻), and hydroxides (OH⁻) are insoluble, except when paired with alkali metals or NH₄⁺.

By utilizing these rules, chemists can anticipate which solutions, when mixed, will result in the formation of a precipitate, aiding in both practical applications and theoretical understanding of chemical behaviors.