Problem 59 - A Complete Resource Book in Chemistry for JEE Main

Question

A bottle completely filled with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is left unstoppered for several days and we observe spontaneous overflow of acid. It is due to (a) dehydration of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (b) absorption of air by \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) hygroscopic nature of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) change in temperature

Step-by-Step Solution

Answer

The overflow is due to the hygroscopic nature of \(\mathrm{H}_{2} \mathrm{SO}_{4}\).

Step 1: Understanding the Nature of Sulfuric Acid

Concentrated sulfuric acid (\(\mathrm{H}_{2} \mathrm{SO}_{4}\)) is a highly hygroscopic substance. This means it has the ability to absorb moisture from the surrounding environment.

Step 2: Analyzing the Effect of Being Unstoppered

When the bottle is left unstoppered, \(\mathrm{H}_{2} \mathrm{SO}_{4}\) starts absorbing moisture from the air due to its hygroscopic nature. This absorption increases the volume of the liquid in the bottle.

Step 3: Identifying the Cause of Overflow

The spontaneous overflow of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) occurs due to this absorption of moisture, which leads to an increase in the volume of the acid, causing it to overflow from the bottle.

Key Concepts

Sulfuric Acid

Sulfuric acid, or \( \mathrm{H}_{2} \mathrm{SO}_{4} \), is a highly significant industrial chemical. It is known for being a strong acid due to its high levels of hydrogen ions. This acidity means it can easily donate protons to other substances. It's one of the most important chemicals produced globally, used in the manufacture of fertilizers, in petroleum refining, and in chemical synthesis. Properties of Sulfuric Acid:

• Corrosive Nature: Sulfuric acid can severely damage metals and skin tissue, necessitating careful handling and storage.
• Concentrated Form: At high concentrations, it is an oily liquid that is very reactive.
• Exothermic Reaction: Mixing sulfuric acid with water releases a lot of heat, often causing the mixture to boil.

Sulfuric acid is essential in many industrial processes but requires respect due to its powerful chemical properties.

Concentration Changes

Concentration refers to the amount of a substance in a given volume or mass of a solution or mixture. When dealing with sulfuric acid, concentration changes are often a result of chemical reactions or external environmental conditions. Factors Affecting Concentration:

• Addition or Removal of Solvent: Adding water to a solution decreases the concentration, while evaporation can increase it.
• Environmental Exposure: When exposed to air, sulfuric acid's hygroscopic nature can cause it to absorb water, thus reducing concentration.
• Reactions with Other Substances: Sulfuric acid can react chemically with other substances, altering its concentration.

Understanding these factors is crucial, especially in industrial and laboratory settings, where maintaining the correct concentration is key to achieving desired reactions and outcomes.

Moisture Absorption

Moisture absorption is the process where a substance takes up water vapor from its environment. This is a common feature in hygroscopic materials, like sulfuric acid, which have a great affinity for water. The Process:

• Hygroscopic materials can absorb moisture from the air. This can be observed when you leave hygroscopic substances exposed to the atmosphere.
• Once moisture is absorbed, the substance undergoes a physical change, often expanding in volume.
• This absorbed moisture can lead to changes in texture and, in the case of acids, concentration.

In practical situations, the hygroscopic nature of sulfuric acid can lead to overflow when left exposed. As it draws in surrounding moisture, its volume increases, potentially causing spillage if the acid is not contained properly. This behavior necessitates careful storage and handling in controlled environments to prevent unwanted chemical interactions and accidents.