Question

A colourless poisonous gas (A) burns with blue flame is passed through aqueous \(\mathrm{NaOH}\) at high pressure and temperature to give a compound (B). (B) on heating gives (C) and (C) gives white precipitate (D) with \(\mathrm{CaCl}_{2}\) both (C) and (D) decolourise acidified \(\mathrm{KMnO}_{4}\). Here (A) can be: (a) \(\mathrm{CO}\) (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{SO}\), (d) \(\mathrm{H}_{2} \mathrm{~S}\)

Short answer

The gas (A) is carbon monoxide (\( \text{CO} \)).

Step-by-step solution

Identify the Gas

The first step is to identify the colourless poisonous gas (A) given in the problem. The gas burns with a blue flame. Among the given options, carbon monoxide ( ext{CO} ) is a known poisonous gas that burns with a blue flame.

React with Aqueous NaOH

Next, the identified gas ext{CO} reacts with aqueous ext{NaOH} at high pressure and temperature. This reaction forms the compound ext{Na}_2 ext{CO}_3 (B). The chemical reaction can be summarized as: ext{CO} + ext{NaOH} ightarrow ext{NaHCO}_3 ightarrow ext{Na}_2 ext{CO}_3 .

Determine the Compound after Heating

When compound (B), ext{Na}_2 ext{CO}_3 , is heated, it gives off compound (C), which is ext{CO}_2 . The reaction is as follows: ext{Na}_2 ext{CO}_3 ightarrow ext{CO}_2 .

React with CaCl2

When ext{CO}_2 (compound C) is reacted with ext{CaCl}_2 , a white precipitate of calcium carbonate ( ext{CaCO}_3 ) is formed, which is compound (D). This reaction can be written as: ext{CO}_2 + ext{CaCl}_2 ightarrow ext{CaCO}_3 .

Decolourising Acidified KMnO4

Both compounds (C) and (D), which are ext{CO}_2 and ext{CaCO}_3 , can decolourise acidified ext{KMnO}_4 solution. This is consistent with the properties of carbonates and carbon dioxide upon reaction in acidic environments.

Key concepts

Gas Reactions

In the realm of inorganic chemistry, understanding gas reactions is crucial. These reactions often involve substances in their gaseous state undergoing a chemical change to form new products. For example, in the given exercise, the gas carbon monoxide (CO) reacts with sodium hydroxide (NaOH) to form sodium carbonate (Na\(_2\)CO\(_3\)). This reaction requires high pressure and temperature, typical for gas reactions involving exchange of ions or molecules. Gas reactions are vital in both natural and industrial processes like combustion, where gases react to emit energy, or in the synthesis of chemicals. Key characteristics of gas reactions include their dependence on pressure, temperature, and the nature of reactants.

• Combustion, as seen with \ ext{CO}, is a common gas reaction.
• Gas reactions can lead to the formation of precipitates or new compounds.
• They often require controlled environments to ensure safety and product yield.

Understanding these reactions helps predict the outcomes of various processes involving gases.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas known for its toxicity. It is formed by the incomplete combustion of carbon-containing fuels, such as natural gas, gasoline, oil, or coal. With its ability to burn with a blue flame, CO is identifiable in many industrial settings where control of combustion is necessary. An essential aspect of CO is its reactivity. For instance, in the exercise described, CO reacts with NaOH to form sodium carbonate, demonstrating its role as a reactant in chemical synthesis.

• CO is dangerous because it binds to hemoglobin, reducing oxygen transport in the body.
• Despite its toxicity, it is useful in applications requiring a reducing atmosphere or synthesis of certain chemicals.
• Proper ventilation and detectors are essential when working with or near CO, especially in industrial environments.

Appreciating the dual nature of CO, being both hazardous and useful, is crucial for its safe handling and application.

Chemical Analysis

Chemical analysis involves identifying the chemical components and composition of substances. In this context, it requires understanding how a gas like carbon monoxide can transform through various reactions. The reaction between CO and NaOH produces Na\(_2\)CO\(_3\), which can be further analyzed by observing its decomposition into CO\(_2\) upon heating. Chemical analysis helps in identifying unknown compounds, determining their concentration, and understanding their reactions, as illustrated in the step-by-step solution.

• Techniques include both qualitative and quantitative analysis.
• Chemical tests often involve reactions leading to visible changes, such as color or precipitate formation.
• Instrumental methods like spectroscopy can provide detailed insights into compound structures and interactions.

Mastery of chemical analysis empowers chemists to elucidate reaction mechanisms and optimize chemical processes.

Precipitation Reactions

Precipitation reactions occur when solutions combine to produce an insoluble solid known as a precipitate. In the exercise, carbon dioxide (CO\(_2\)), acts as the intermediary in forming the white precipitate, calcium carbonate (CaCO\(_3\)), when reacted with calcium chloride (CaCl\(_2\)). Such reactions are invaluable in areas such as water treatment, qualitative analysis, and extraction of metals. They are typically straightforward to identify, as they usually result in a visible change within the reaction mixture, like a color or texture change.

• Precipitation reactions are driven by the insolubility of the product in water.
• The appearance of a solid indicates a chemical change has occurred.
• These reactions have practical applications, from manufacturing to environmental science.

Understanding how these reactions occur aids in predicting product formation and informs various industrial and laboratory processes.