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Asolidsamplehasapproximately equalamounts of two or more of the following soluble salts: \(\mathrm{AgNO}_{3}, \mathrm{ZnCl}_{2}, \mathrm{~K}_{2} \mathrm{CO}_{3}, \mathrm{MgSO}_{4}, \mathrm{Ba}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\), and \(\mathrm{NH}_{4} \mathrm{NO}_{3} .\) A sample of the solid, sufficient to give at least 0.04 moles of any single salt, is added to \(100 \mathrm{~mL}\) of water, yielding a white precipitate and a clear solution. The precipitate is collected and rinsed with water. When a portion of the precipitate is placed in dilute \(\mathrm{HNO}_{3}\) it completely dissolves, leaving a colorless solution. A second portion of the precipitate is placed in dilute \(\mathrm{HCl}\), yielding a solid and a clear solution; when its filtrate is treated with excess \(\mathrm{NH}_{3}\), a white precipitate forms. Identify the salts that must be present in the sample, the salts that must be absent, and the salts for which there is insufficient information to make this determination. \({ }^{13}\)

Step by step solution

01

Analyze the Initial Solution and Precipitate

First, we need to recognize which of the given salts can form a white precipitate when added to water. By examining solubility rules, we note that AgNO鈧�, ZnCl鈧�, NH鈧凬O鈧�, Ba(C鈧侶鈧僌鈧�)鈧�, and MgSO鈧� are generally soluble in water, while K鈧侰O鈧� can react to form insoluble precipitates. In this context, Ag鈦� can precipitate as AgCl in the presence of Cl鈦�.

02

Reaction with Dilute HNO鈧�

When the precipitate dissolves in dilute HNO鈧� with no further solid formation, it indicates the presence of a compound like AgCl, which readily dissolves in nitric acid due to formation of soluble complexes.

03

Reaction with Dilute HCl

Upon adding dilute HCl, the formation of a solid implies that the precipitate contained a component that can re-precipitate, such as Zn(OH)鈧�, as Zn虏鈦� may form insoluble ZnCl鈧� in the presence of excess HCl. However, the presence of a solid might also include AgCl, which is already identified as soluble. The formation of a clear solution suggests a separation of soluble components.

04

Reaction with NH鈧�

The addition of excess NH鈧� resulting in a white precipitate indicates the formation of complexes like AgOH converting partially back to AgCl, as AgCl is poorly soluble in NH鈧勨伜 solutions, forming Ag鈦� ions which then react with NH鈧�.

05

Identify Present, Absent, and Unknown Salts

Based on the given reactions and solubility rules: - **Present:** AgNO鈧� (formation of AgCl as a precipitate). - **Absent:** K鈧侰O鈧�, MgSO鈧�, Ba(C鈧侶鈧僌鈧�)鈧�, and NH鈧凬O鈧� (since they are not indicated by precipitate behavior). - **Insufficient Information:** ZnCl鈧� (certain Zn虏鈦� behaviors are suggested but not definitive for presence or absence due to mixed complex possibilities).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Solubility Rules

Understanding solubility rules is crucial for predicting how different salts behave in water. Solubility rules help determine which compounds will dissolve and which will remain as solid precipitates.
Here's a quick guide:

• Nitrates ( O_3^- ) and acetates ( C_2H_3O_2^- ) are generally soluble in water.
• Chlorides (Cl鈦�) are typically soluble, except for AgCl, PbCl鈧�, and Hg鈧侰l鈧�.
• Sulfates ( SO_4^{2-}) are mostly soluble, with exceptions like BaSO鈧�, PbSO鈧�, and CaSO鈧�.
• Carbonates ( CO_3^{2-}) are usually insoluble, except with alkali metals like Na鈦� and K鈦�.
• Ammonium ( NH_4^+) salts and alkali metal salts are soluble.

Using these rules, we can predict which salts in the list are soluble and identify potential precipitates.

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble product or precipitate. In the given exercise, AgNO鈧� is mixed with a Cl鈦� source, creating AgCl, which appears as a white precipitate.
A solid forming in this way, signifies that a potential reaction is taking place. Precise knowledge about solubility helps us anticipate such outcomes.
Notably, precipitation reactions are key for:

• Identifying unknown ions in a solution.
• Purifying substances by removing undesired ions.

When AgCl forms a precipitate, it can be dissolved in dilute HNO鈧�, indicating how precipitation reactions are reversible under certain conditions.

Salt Identification

Salt identification involves examining the reactions and solubility of compounds. In the exercise, the mixture contains various salts, requiring a systematic approach to identify the present and absent salts.
Let's break this down:

• Silver nitrate ( AgNO_3) is confirmed present due to the formation of AgCl when reacting with chlorides.
• The formation of a white precipitate with NH_3 suggests the re-precipitation of AgCl from a dissolved form.
• The absence of reactions indicating carbonate (K_2CO_3) behavior suggests its non-presence.

By analyzing these reactions, we confirm or refute the presence of each salt, helping in salt identification and analysis.

Complex Ion Formation

Complex ion formation is a fascinating process where metal ions in a solution form complex structures with molecules or ions, often affecting solubility.
In your experiment, complex ion formation plays a critical role. For instance, when Ag鈦� ions react with excess NH鈧�, they can form [Ag(NH_3)_2]^+, a soluble complex. The formation and breakdown of such complexes affect the solution's composition and appearance.
Key insights include:

• Complex ions can significantly alter the behavior of salts in solution.
• They often explain how precipitates dissolve and re-form under different conditions.

Complex ion formation allows chemists to manipulate solution conditions and separate ions effectively, showcasing the utility of combining chemical principles with practical techniques.