Question

To a clear solution of compound \((\mathrm{X})\), a solution of \(\mathrm{BaCl}_{2}\) is precipitate is formed which does not dissolve in dil. HCl. The compound \((X)\) is a (a) nitrate (b) bromide (c) sulphate (d) carbonate

Short answer

The compound \((X)\) is a sulphate (c).

Step-by-step solution

Understanding the Reaction

When barium chloride (\(\text{BaCl}_2\)) is added to a solution of compound \((X)\) and a precipitate is formed, this suggests the formation of a very insoluble compound. BaCl2 is commonly used to test for the presence of sulphates, carbonates, and other anions that form insoluble barium salts.

Identifying the Precipitate

The possible precipitate formed here could be barium sulphate (\(\text{BaSO}_4\)) or barium carbonate (\(\text{BaCO}_3\)). Both of these are insoluble in water.

Testing Solubility with Dilute HCl

Barium carbonate, unlike barium sulphate, will react with dilute HCl to form soluble components (carbon dioxide and soluble barium chloride). However, barium sulphate is known for being insoluble in dilute HCl.

Conclusion Based on Reaction Behavior

Since the precipitate does not dissolve in dilute HCl, it is likely to be barium sulphate. Therefore, compound \((X)\) must be a sulphate.

Key concepts

Barium Chloride Test

The barium chloride test is a common method used in chemistry to identify the presence of certain anions that form insoluble compounds with barium ions. When \( ext{BaCl}_2\) is added to a solution, it reacts by releasing barium ions (Ba\(^{2+}\)). These barium ions interact with negative ions present in the solution.

This reaction mechanism is especially useful for identifying anions like sulfate (SO\(^{2-}_4\)), carbonate (CO\(^{2-}_3\)), and others. If any of these anions are present, a white precipitate of an insoluble barium salt is likely to form. The barium chloride test is highly valued due to its simplicity and the clear visual cue provided by the precipitate formation.

In educational settings, it aids students in understanding how ionic interactions can lead to precipitation reactions, offering a hands-on illustration of solubility principles.

Insoluble Compounds

Insoluble compounds are those that do not dissolve easily in solvents, like water. When certain ionic compounds are mixed in a solution, they might react to form a new substance that is not soluble.

Insolubility primarily depends on the internal ionic structure of the compound and the types of ions involved. For instance:

• Barium sulfate (\(\text{BaSO}_4\)) is an example of an insoluble compound due to its strong ionic bonds preventing it from dissolving in water.
• In contrast, compounds like barium chloride (\(\text{BaCl}_2\)) are soluble in water because they have weaker ionic bonds that dissociate easily.

This distinction is crucial in chemical analysis, as it predicts which reactions will produce visible results, such as a precipitate.

Reaction with HCl

Hydrochloric acid (HCl) is widely used in reactions to test the solubility of different compounds. When applied to a precipitate, HCl can help determine if the substance is a carbonate or sulfate.

Here's how it works:

• Barium carbonate (\(\text{BaCO}_3\)) reacts with dilute HCl to dissolve, with carbon dioxide gas being released as a byproduct.
• Conversely, barium sulfate (\(\text{BaSO}_4\)) remains unchanged because it does not react with HCl. This inability to dissolve in HCl is what characterizes certain barium salts as highly insoluble.

Such reactions are fundamental in confirming the identity of the compound formed in solution, as seen in the original exercise. It’s particularly valuable for educational purposes, demonstrating principles of reaction, solubility, and gas evolution.

Sulfate Identification

Identifying sulfates in a solution often involves the use of a barium chloride test, followed by further analysis such as reaction with dilute HCl. Sulfates form very stable and white precipitates with barium ions.

The non-reactivity of this precipitate with HCl confirms its identity as barium sulfate (\(\text{BaSO}_4\)). Here’s a step-by-step of sulfate identification:

• Introduce barium chloride to the sample solution. If sulfates are present, a white precipitate immediately forms.
• The next step is adding dilute HCl to check the solubility of the precipitate. A lack of dissolution confirms the presence of sulfates.

Such confirmatory tests are crucial in chemistry, providing definitive qualitative information about unknown samples. Recognizing sulfate through such tests is a fundamental skill in chemical analysis, easily demonstrating how reactivity differs among compounds.