Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is not dissolve by dil HCl? (a) \(\mathrm{MnS}\) (b) \(\mathrm{ZnS}\) (c) \(\mathrm{BaSO}_{4}\) (d) \(\mathrm{BaSO}_{3}\)

Step-by-Step Solution

Answer

BaSO₄ does not dissolve in dilute HCl.

Step 1: Understanding the Question

We need to determine which of the given compounds does not dissolve in dilute Hydrochloric Acid (HCl). The options provided are MnS, ZnS, BaSO₄, and BaSO₃.

Step 2: Identifying Solubility Principles

Most sulfides (such as MnS and ZnS) tend to be insoluble or have limited solubility in water, but many will react with acids to form soluble hydrogen sulfides. Sulfates like BaSO₄, on the other hand, are particularly known for their low solubility in water and dilute acids.

Step 3: Applying the Solubility Concept

BaSO₄ (Barium sulfate) is well-known for being insoluble in water and dilute acids, unlike some other sulfides and the compound BaSO₃. Therefore, BaSO₄ will not dissolve in dilute HCl, while the other compounds typically will react or dissolve to some extent.

Key Concepts

Sulfide Solubility

Sulfides are compounds where sulfur is combined with a metal or semimetal. Understanding the solubility of sulfides in water or acids can help predict the behavior of materials in chemical reactions. Broadly, sulfides have limited solubility in water. Metals such as zinc and manganese form sulfides ( MnS, ZnS) that do not dissolve easily in water. However, these sulfides can often react with acids. When treated with dilute hydrochloric acid (HCl), these metal sulfides can produce hydrogen sulfide gas.

• **Zinc Sulfide (ZnS)**: Although generally insoluble in water, ZnS reacts with dilute HCl to form soluble compounds and release hydrogen sulfide gas.
• **Manganese Sulfide (MnS)**: Similar to ZnS, MnS dissolves in acids like HCl, where it forms soluble manganese chloride and releases hydrogen sulfide gas.

These reactions are important in laboratory settings where sulfide ion behavior is analyzed.

Sulfate Solubility

Sulfates are salts or esters of sulfuric acid containing the anion SO₄²⁻. The solubility of sulfates varies significantly across different metal ions. When evaluating compounds for solubility, barium sulfate ( BaSO₄) is a classic example of an insoluble sulfate.

• **Barium Sulfate (BaSO₄)**: Known for its extremely low solubility in water and acids, BaSO₄ remains undissolved even in the presence of strong or dilute acids like HCl.
• **Barium Sulfite (BaSO₃)**: While BaSO₃ shares some chemical similarities to BaSO₄, its behavior in acids like HCl is different. It tends to react more readily, slowly dissolving over time.

Understanding these solubility behaviors is crucial for applications like pharmaceuticals, where BaSO₄’s inertness is used as a contrast agent in X-ray imaging.

Hydrochloric Acid Reactions

Hydrochloric acid (HCl) is a strong acid known for its reactivity. When HCl interacts with different compounds, varied reactions occur depending on the chemical nature of the compounds involved. In the case of sulfides and sulfates, HCl can cause different behaviors based on each compound’s solubility properties.

• With **sulfides** like ZnS and MnS, HCl typically leads to a reaction that produces hydrogen sulfide gas, demonstrating the solubility increase when sulfides meet acids.
• For **sulfates**, particularly BaSO₄, dilute HCl does not facilitate dissolution due to the compound's inherent properties. This non-reactivity reflects in its constant precipitation in solutions.

These interactions are vital in both academic and industrial chemistry settings. They help highlight how even strong acids like HCl can leave certain compounds unchanged due to intrinsic solubility constraints.