Problem 15 - Chemistry in 30 days

Question

On heating a mixture of \(\mathrm{NaCl}, \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}\), and cone. \(\mathrm{H}_{2} \mathrm{SO}_{4}\), which of the following is formed ? (a) \(\mathrm{CrCl}_{3}\) (b) \(\mathrm{CrO}_{2} \mathrm{Cl}_{2}\) (c) \(\mathrm{Cl}_{2}\) (d) \(\mathrm{NilClO}_{2}\)

Step-by-Step Solution

Answer

The formed compound is \(\mathrm{CrO}_2\mathrm{Cl}_2\) (Option b).

Step 1: Identify the Reaction Components

We need to identify the components involved in the reaction. The reaction involves sodium chloride (\(\mathrm{NaCl}\)), potassium dichromate (\(\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7\)), and concentrated sulfuric acid (\(\mathrm{H}_2\mathrm{SO}_4\)).

Step 2: Reaction Analysis

On heating the mixture, the potassium dichromate (\(\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7\)) reacts with concentrated sulfuric acid to form chromium oxide dichloride \((\mathrm{CrO}_2\mathrm{Cl}_2)\). The reaction is: \[\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7 + \mathrm{NaCl} + 2\mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{CrO}_2\mathrm{Cl}_2\]

Step 3: Identify the Product Formed

As a result of the reaction, among the given options, chromium oxide dichloride \((\mathrm{CrO}_2\mathrm{Cl}_2)\) is formed.

Step 4: Conclusion

The formed compound from the reaction is chromium oxide dichloride \((\mathrm{CrO}_2\mathrm{Cl}_2)\) which corresponds to option (b).

Key Concepts

Potassium Dichromate Reactions

Potassium dichromate, represented as \(\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7\), is a powerful oxidizing agent used in various chemical reactions. One key feature of potassium dichromate is its ability to facilitate reactions by providing oxygen atoms, which aid in the oxidation process.
In the presence of concentrated sulfuric acid, potassium dichromate acts aggressively to transform other chemical constituents. When heated, it reacts with the concentrated \(\mathrm{H}_2\mathrm{SO}_4\), contributing to the formation of chromium oxide dichloride (\(\mathrm{CrO}_2\mathrm{Cl}_2\)) by oxidizing the chloride ions from sodium chloride.

• Potassium dichromate itself is orange-red in color and often used in various industries like leather tanning and wood staining, demonstrating its wide practical application.

Overall, the reaction of potassium dichromate with sulfuric acid is crucial for generating essential intermediate chemical products.

Sodium Chloride Reaction

Sodium chloride, or common table salt \((\mathrm{NaCl})\), plays a significant role in various chemical reactions beyond our everyday dining tables. When mixed with strong acids like concentrated sulfuric acid, sodium chloride contributes to interesting reaction processes.
In the presence of both \(\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7\) and \(\mathrm{H}_2\mathrm{SO}_4\), sodium chloride provides the necessary chloride ions that are crucial for forming chromium oxide dichloride (\(\mathrm{CrO}_2\mathrm{Cl}_2\)).

• In this reaction, the \(\mathrm{NaCl}\) essentially acts as a source of chloride, which pairs with chromic acid components to form the volatile product, chromium oxide dichloride.

Thus, sodium chloride acts as more than just "salt" in the kitchen but serves as a vital reactant in synthesizing key chemical compounds.

Sulfuric Acid Chemistry

Sulfuric acid \((\mathrm{H}_2\mathrm{SO}_4})\) is one of the most important industrial chemicals, known for its strong acidic nature and its ability to act as both an oxidizing and dehydrating agent. In chemical reactions, especially those involving heating, sulfuric acid facilitates the breakdown and combination of reactants to form new chemical entities.
In the reaction with potassium dichromate and sodium chloride, concentrated sulfuric acid breaks down the \(\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7\) to release chromium and works with \(\mathrm{NaCl}\) to form \(\mathrm{CrO}_2\mathrm{Cl}_2\).

• The concentration and temperature are critical factors that ensure the appropriate reactions occur efficiently, allowing for the complete transformation and formation of \(\mathrm{CrO}_2\mathrm{Cl}_2\).

Each parameter in sulfuric acid chemistry plays a pivotal role in determining the success and direction of the chemical processes it is involved in.