Problem 19 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

A gas ' \(\mathrm{X}^{\prime}\) is passed through water to form a saturated solution. The aqueous solution on treatment with silver nitrate gives a white precipitate. The saturated aqueous solution also dissolves magnesium ribbon with evolution of a colourless gas ' \(\mathrm{Y}\) '. Identify ' \(\mathrm{X}^{\prime}\) and 'Y' (a) \(\mathrm{X}=\mathrm{CO}_{2}, \mathrm{Y}=\mathrm{Cl}_{2}\) (b) \(\mathrm{X}=\mathrm{Cl}_{2}, \mathrm{Y}=\mathrm{CO}_{2}\) (c) \(\mathrm{X}=\mathrm{Cl}_{2}, \mathrm{Y}=\mathrm{H}_{2}\) (d) \(\mathrm{X}=\mathrm{H}_{2}, \mathrm{Y}=\mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (c): \(X = Cl_2\), \(Y = H_2\).

Step 1: Analyze Silver Nitrate Reaction

The problem states that the aqueous solution gives a white precipitate with silver nitrate. This suggests the presence of chloride ions, as silver chloride (AgCl) is a white precipitate. This indicates that the gas \(X\) could be \(Cl_2\), which dissolves in water forming hydrochloric acid (\(HCl\)).

Step 2: Analyze Magnesium Reaction

The aqueous solution with \(X\) dissolves magnesium ribbon releasing a colorless gas \(Y\). Magnesium reacts with \(HCl\) formed from dissolved \(Cl_2\) to produce \(MgCl_2\) and hydrogen gas \(H_2\). \(H_2\) is colorless, consistent with \(Y\).

Step 3: Identify \(X\) and \(Y\)

Based on the silver nitrate test and the magnesium reaction, \(X\) must be \(Cl_2\) as it forms \(HCl\) producing \(AgCl\) and releases \(H_2\) gas when reacting with magnesium. Thus, \(X = Cl_2\) and \(Y = H_2\).

Step 4: Compare Options

From the provided choices, option (c), which states \(X = Cl_2\) and \(Y = H_2\), matches our analysis. The other options don't align with the precipitate or gas evolution results.

Key Concepts

Precipitation Reactions

Precipitation reactions occur when ions in solution combine to form an insoluble compound. These reactions are a common way to identify the presence of specific ions. In this exercise, the aqueous solution reacts with silver nitrate to yield a white precipitate. This is a classic example of a precipitation reaction, where silver nitrate

• combines with chloride ions
• forms silver chloride (AgCl)
• AgCl is the white precipitate formed in the reaction

When presented with a clear solution, witnessing the formation of a solid indicates that an insoluble salt has formed. This phenomenon is a clue to the presence of chloride ions, which arise from gases like chlorine that dissolve in water to form chlorides. Understanding these reactions help in identifying unknown substances based on their reaction outcomes, such as the formation of precipitates.

Gas Evolution

Gas evolution reactions are fascinating processes where chemical reactions produce gas as a product. In this problem, the aqueous solution containing the gas \(X'\) dissolves magnesium ribbon, resulting in the emission of a colorless gas \(Y\). This is an example of a gas evolution reaction. When magnesium reacts with hydrochloric acid (formed from dissolved chlorine gas in the water), hydrogen gas \(H_2\) is released. Let's break it down further:

• Magnesium \((Mg)\) reacts with hydrochloric acid \((HCl)\)
• The reaction produces magnesium chloride \((MgCl_2)\)
• Hydrogen gas \((H_2)\) is the evolved gas, colorless in nature

This process illustrates the typical behavior of metals reacting with acids to release hydrogen gas. Special attention to gas evolution can help identify and confirm the nature of gases involved in reactions.

Chlorine Chemistry

Chlorine chemistry plays a crucial role in various chemical processes, especially in industrial and laboratory settings. Chlorine gas \( (Cl_2) \) is central to this exercise, serving multiple functions such as disinfectant properties, bleaching agent, and a reagent to form other compounds in chemical reactions. In the context of this exercise:

• Chlorine gas dissolves in water to form hydrochloric acid \((HCl)\)
• Hydrochloric acid provides chloride ions, which precipitate silver chloride \((AgCl)\)
• It also interacts with metals like magnesium to release hydrogen gas \((H_2)\)

Understanding the behavior of chlorine in reactions is essential. It helps in the identification and manipulation of various chemical processes, as chlorine derivatives participate in numerous applications. Mastering its properties and reactions provides foundational knowledge for students studying chemistry.