Problem 111 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{H}_{2} \mathrm{SO}_{4}\) is not used for the preparation of \(\mathrm{CO}_{2}\) from marble chips because (a) calcium sulphate is sparingly soluble and get deposited on marble chips and stops the reaction (b) it does not react (c) the reaction is vigorous (d) huge amount of heat is evolved

Step-by-Step Solution

Answer

Option (a): Calcium sulfate is sparingly soluble and deposits on marble chips, stopping the reaction.

Step 1: Understanding the Reaction

When marble chips, or calcium carbonate ( ext{CaCO}_3), react with sulfuric acid ( ext{H}_2 ext{SO}_4), calcium sulfate ( ext{CaSO}_4), water ( ext{H}_2 ext{O}), and carbon dioxide ( ext{CO}_2) are formed. The reaction can be written as: \[ \text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2 \]

Step 2: Assessing the Solubility of Calcium Sulfate

Calcium sulfate ( ext{CaSO}_4) is sparingly soluble in water. This means it does not dissolve well and can easily form a solid precipitate. When sparingly soluble substances form, they can coat surfaces involved in the reaction, such as marble chips, and hinder further reaction.

Step 3: Recognizing the Impeding Effect

Since calcium sulfate forms a coating on the marble chips, it can effectively block the sulfuric acid from reacting with more of the calcium carbonate. This leads to stopping the reaction prematurely, even if there is still acid and marble available to react.

Step 4: Choosing the Correct Option

Considering that calcium sulfate's limited solubility leads it to deposit on the marble chips and thus hinders the reaction, the correct reason why \( ext{H}_2 ext{SO}_4\) is not used is option (a): calcium sulfate is sparingly soluble and gets deposited on marble chips and stops the reaction.

Key Concepts

Calcium Carbonate

Calcium carbonate, with the chemical formula \(\text{CaCO}_3\), is a common substance found in rocks such as limestone, marble, and chalk. It is used in various industrial and scientific applications. Marble chips, a form of calcium carbonate, are often used in experiments due to their relatively pure composition. Calcium carbonate is known for its reactivity with acids, where it produces carbon dioxide when reacting.

• Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated.
• In the presence of acids, it release carbon dioxide gas, a key aspect when generating \(\text{CO}_2\) in laboratory conditions.
• The reaction between calcium carbonate and sulfuric acid is an example of an acid-carbonate reaction.

The interaction with sulfuric acid is less efficient for producing \(\text{CO}_2\) due to calcium sulfate formation, which may hinder the reaction process.

Sulfuric Acid

Sulfuric acid, with the chemical formula \(\text{H}_2\text{SO}_4\), is a strong mineral acid with a wide range of industrial uses. Known for its robust dehydrating properties, it can cause exothermic reactions.

• It is a highly corrosive acid, capable of reacting with both organic and inorganic substances.
• In its concentrated form, sulfuric acid can lead to dehydration of organic materials.
• When diluted, it acts primarily as an oxidizing acid, reacting vigorously with various substances.

During the reaction with calcium carbonate, sulfuric acid reacts to form a solid precipitate of calcium sulfate which affects the overall efficiency and continuation of the chemical reaction.

Reaction Solubility

Reaction solubility plays a critical role in determining the progress of a chemical reaction, especially when a solid precipitate forms. In the context of the reaction between calcium carbonate and sulfuric acid, the formation of calcium sulfate plays a decisive role.

• Calcium sulfate, \(\text{CaSO}_4\), which forms as a byproduct, is sparingly soluble in water.
• Since it does not dissolve easily, it can form a coating on the marble chips, effectively blocking further reaction.
• This precipitate formation is a common issue when reactions produce substances with low solubility. It can lead to the premature cessation of the reaction.

Understanding solubility in reactions is crucial for predicting and controlling the outcomes, especially in laboratory settings where efficiency is paramount.