Problem 29 - Chemistry: The Central Science in SI Units, Global Edition

Question

You know that an unlabeled bottle contains an aqueous solution of one of the following: \(\mathrm{AgNO}_{3}, \mathrm{CaCl}_{2},\) or \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3} . \mathrm{A}\) friend suggests that you test a portion of the solution with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) and then with 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.

Step-by-Step Solution

Answer

(d) More than one, but not all, of the reactions described in answers a-c could occur. The possible precipitates include Barium sulfate, indicating the presence of \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) in the unknown solution, and Silver chloride, indicating the presence of \(\mathrm{AgNO}_{3}\) in the unknown solution.

Step 1: Analyze the first reaction with Ba(NO3)2

First, we will analyze the possible reactions of the unknown solution with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) solution. Let's examine the first possible reaction: If \(\mathrm{AgNO}_{3}\) is present, the reaction with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) occurs as follows: \(\mathrm{AgNO}_{3}(aq) + \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(aq) → \mathrm{AgNO}_{3}(aq) + \mathrm{Ba}(\mathrm{NO}_{3})_{2}(aq)\) No precipitate forms in this reaction.

Step 2: Analyze the second reaction with Ba(NO3)2

If \(\mathrm{CaCl}_{2}\) is present, the reaction with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) occurs as follows: \(\mathrm{CaCl}_{2}(aq) + \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(aq) → \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(aq) + \mathrm{BaCl}_{2}(aq)\) No precipitate forms in this reaction as well.

Step 3: Analyze the third reaction with Ba(NO3)2

Finally, if \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) is present, the reaction with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) occurs as follows: \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}(aq) + 3\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(aq) → 3\mathrm{BaSO}_{4}(s) + 2\mathrm{Al}(\mathrm{NO}_{3})_{3}(aq)\) Here, we have precipitation reaction forming a solid, Barium sulfate: \[\mathrm{3BaSO}_{4}(s)\] So after testing with \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\), if a precipitate forms, we know that the mystery solution contains \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\).

Step 4: Analyze the reaction with NaCl

Now, let's analyze the possible reactions of the unknown solution with NaCl solution. If \(\mathrm{AgNO}_{3}\) is present, the reaction with NaCl occurs as follows: \(\mathrm{AgNO}_{3}(aq) + \mathrm{NaCl}(aq) → \mathrm{AgCl}(s) + \mathrm{NaNO}_{3}(aq)\) Here, a precipitate of Silver chloride: \[\mathrm{AgCl}(s)\] forms. If the other two samples are tested, no precipitate will form. So if a precipitate forms after the reaction with NaCl, it means the mystery solution contains \(\mathrm{AgNO}_{3}\).

Step 5: Determine the correct answer

From the analysis, we can conclude that: - Barium sulfate could precipitate, which indicates the presence of \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) in the unknown solution. - Silver chloride could precipitate, which indicates the presence of \(\mathrm{AgNO}_{3}\) in the unknown solution. Thus, the correct answer is: (d) More than one, but not all, of the reactions described in answers a-c could occur.

Key Concepts

Precipitation Reactions

Precipitation reactions are fascinating chemical processes involving the formation of a solid within a liquid solution. This solid, known as a "precipitate," is generally an insoluble compound that is separated from the rest by the action of the reaction. In the given exercise, the concept of precipitation is demonstrated when analyzing reactions involving barium sulfate and silver chloride.
Barium sulfate (\[\text{BaSO}_4(s)\]) forms as a precipitate when aluminum sulfate is mixed with barium nitrate, indicating the presence of aluminum sulfate in the unknown solution.
Similarly, silver chloride (\[\text{AgCl}(s)\]) precipitates from the reaction between silver nitrate and sodium chloride. Recognizing these reactions helps in identifying the components of unknown solutions based on the visible formation of solid precipitates.
Precipitation reactions play a crucial role in various applications, including water purification, medical diagnostics, and the isolation of compounds in chemical laboratories. These reactions are important tools for chemists to analyze and differentiate mixtures.

Reaction Analysis

Reaction analysis is a critical skill in chemistry, allowing one to predict the outcome of mixing different chemical substances. By applying knowledge of solubility rules and reactivity, chemists can anticipate whether a precipitate will form during a reaction.
In the context of the exercise, reaction analysis was employed to determine which combination of chemicals will produce a visible change. When the unknown solution was tested with \[\text{Ba(NO}_3)_2\]) and \[\text{NaCl}\]), careful consideration of reaction possibilities guided the chemists to identify the solutions.

• Using the solubility rules, the chemists identified that neither a reaction occurs nor a precipitate forms in the case of calcium chloride with barium nitrate.
• A clear-winged decision on precipitate formation pointed to aluminum sulfate and silver nitrate when the right partners were added.

Breaking down the steps and potential reactions piece by piece allows the observer to conclude effectively which compounds are present. These skills are essential across scientific and industrial disciplines for optimizing processes and ensuring the safety and reliability of chemical usage.

Aqueous Solutions

Aqueous solutions are a medium in which many chemical reactions occur. They consist of substances dissolved in water, which acts as a solvent to facilitate the interaction between molecules and ions. The particular nature of these solutions often determines the pathway for chemical reactions, including the ones discussed in the exercise above.
The role of aqueous solutions is to enable molecules or ions to move freely and interact, which is crucial for precipitation reactions. In the given exercise, unknown solutions of \[\text{AgNO}_3\]), \[\text{CaCl}_2\]), and \[\text{Al}_2( ext{SO}_4)_3\]) were tested within aqueous solutions to observe the formation of a precipitate under specific circumstances.
Most reactions in biological and chemical systems take place in aqueous environments because water is a universal solvent due to its ability to dissolve a wide array of substances. This unique property makes aqueous solutions essential components in biological systems, environmental science, and industrial processes.