Question

Which of the following cannot show acidic nature? (a) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (b) \(\mathrm{CaCO}_{3}\) (c) \(\mathrm{HCl}\) (d) \(\mathrm{HSO}_{4}^{-}\)

Short answer

a) H2CO3 b) CaCO3 c) HCl d) HSO4- Answer: b) CaCO3

Step-by-step solution

Identify substance's characteristics

For each substance, we need to analyze its formula and determine if it can dissociate to produce H+ ions when in an aqueous solution. Let's examine each substance: (a) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) - Carbonic acid: It has H+ ions and can therefore show acidic nature. (b) \(\mathrm{CaCO}_{3}\) - Calcium carbonate: It does not have H+ ions in its structure and cannot dissociate into H+ ions in the solution. (c) \(\mathrm{HCl}\) - Hydrochloric acid: It has H+ ions in its structure and can dissociate into H+ ions in the solution, thus it can show acidic nature. (d) \(\mathrm{HSO}_{4}^{-}\) - Bisulfate ion: It has H+ ions and can dissociate into H+ ions in the solution, therefore it can show acidic nature.

Identify the substance that cannot show acidic nature

As we have analyzed the chemical formulas of each substance, we have determined that option (b) \(\mathrm{CaCO}_{3}\) (Calcium carbonate) is the substance that cannot show acidic nature as it does not have H+ ions in its structure and cannot dissociate into H+ ions in the solution. So, the correct answer is \(\mathrm{CaCO}_{3}\) (option b).

Key concepts

H+ ions

The presence of H⁺ ions is a key indicator of a substance's acidic nature. These ions, known as hydrogen ions, are what give acids their characteristic properties. When a substance contains H⁺ ions, it can potentially exhibit acidity.
In a chemical reaction or in an aqueous solution, these ions can be released, contributing to the acidic behavior of the substance. For instance:

• Hydrochloric acid (HCl): Contains H⁺ ions and readily releases them.
• Carbonic acid (H₂CO₃): Also contains H⁺ ions that can contribute to acidity.

Understanding H⁺ ions helps in determining whether a substance can undergo reactions that result in an acidic environment.

Dissociation

Dissociation is the process by which a compound breaks down into smaller components, often ions, when it is dissolved in a solvent such as water. This process is essential for identifying the acidic nature of a substance.
When acids dissociate, they often release H⁺ ions into the solution, increasing the solution's acidity. Let's consider a few examples:

• HCl: Fully dissociates into H⁺ and Cl^- ions, making it a strong acid.
• H₂CO₃: Partially dissociates into H⁺ and HCO₃^- ions, showing weak acidic properties.

Understanding dissociation helps us predict how substances behave when mixed with water.

Aqueous Solution

An aqueous solution is a solution where water is the solvent. In such solutions, various substances can completely or partially dissolve.
Water, with its polar nature, is an excellent solvent for many ionic compounds. When acids are dissolved in water, they typically dissociate to release H⁺ ions, illustrating their acidic nature.
For example:

• HCl: Dissolves completely in water, leading to a high concentration of H⁺ ions.
• CaCO₃: It does not dissolve well in water, nor does it release H⁺ ions, explaining why it cannot exhibit acidity.

Aqueous solutions are crucial for understanding chemical reactions in biological and environmental contexts.

Chemical Formulas

Chemical formulas provide important information about the composition and nature of substances. They indicate the elements present and the number of atoms of each element.
Analyzing chemical formulas helps us predict whether a compound can show acidic behavior.

• H₂CO₃ (Carbonic acid): Contains hydrogen atoms that can form H⁺ ions, showing acidity.
• CaCO₃ (Calcium carbonate): Lacks hydrogen atoms that can dissociate as H⁺ ions, so it does not exhibit acidic nature.

By examining chemical formulas, we can understand more about the reactivity and properties of different substances.