Problem 171 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following on thermal - decomposition yields a basic as well as an acidic oxide? (a) \(\mathrm{CaCO}_{3}\) (b) \(\mathrm{NaNO}_{3}\) (c) \(\mathrm{KClO}_{3}\) (d) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\)

Step-by-Step Solution

Answer

None of the options form both a basic and an acidic oxide upon thermal decomposition.

Step 1: Understand Thermal Decomposition

Thermal decomposition is a chemical reaction where a compound breaks down into simpler substances when heated. In this exercise, we are looking for a compound that decomposes into both a basic and an acidic oxide upon heating.

Step 2: Analyze Option (a) Calcium Carbonate

Calcium carbonate (\(\mathrm{CaCO}_{3}\)) undergoes thermal decomposition to form calcium oxide (\(\mathrm{CaO}\)) and carbon dioxide (\(\mathrm{CO}_{2}\)). The reaction is:\[\mathrm{CaCO}_{3}(s) \rightarrow \mathrm{CaO}(s) + \mathrm{CO}_{2}(g)\]Calcium oxide is a basic oxide, but carbon dioxide is not an oxide in the typical sense, making this option incorrect.

Step 3: Analyze Option (b) Sodium Nitrate

Sodium nitrate (\(\mathrm{NaNO}_{3}\)) decomposes upon heating to yield sodium nitrite (\(\mathrm{NaNO}_{2}\)) and oxygen (\(\mathrm{O}_{2}\)). The reaction is:\[2\mathrm{NaNO}_{3}(s) \rightarrow 2\mathrm{NaNO}_{2}(s) + \mathrm{O}_{2}(g)\]This creates only a basic oxide, so this option is incorrect.

Step 4: Analyze Option (c) Potassium Chlorate

Potassium chlorate (\(\mathrm{KClO}_{3}\)) decomposes to form potassium chloride (\(\mathrm{KCl}\)) and oxygen (\(\mathrm{O}_{2}\)). The reaction can be written as:\[2\mathrm{KClO}_{3}(s) \rightarrow 2\mathrm{KCl}(s) + 3\mathrm{O}_{2}(g)\]This reaction does not yield any oxides; hence, this option is incorrect.

Step 5: Analyze Option (d) Ammonium Nitrate

Ammonium nitrate (\(\mathrm{NH}_{4} \mathrm{NO}_{3}\)) when decomposed, yields nitrous oxide (\(\mathrm{N}_{2}\mathrm{O}\)) and water vapor (\(\mathrm{H}_{2}\mathrm{O}\)), not oxides. Since nitrous oxide is not considered a basic oxide, this option is incorrect.

Key Concepts

Acidic Oxides

Acidic oxides are compounds that, when combined with water, form acidic solutions. These oxides mostly come from non-metal elements, such as sulfur and carbon. A classic example is carbon dioxide (\(\text{CO}_2\)), which forms carbonic acid when dissolved in water:

• \(\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3\)

These oxides generally react with bases to produce salts. For instance, when sulfur dioxide (\(\text{SO}_2\)) combines with calcium hydroxide (a base):

• \(\text{SO}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaSO}_3 + \text{H}_2\text{O}\)

Acidic oxides are primarily found among non-metallic oxides, which are crucial in various industrial processes, such as the manufacture of fertilizers and in the metal refining industry.

Basic Oxides

Basic oxides are the opposite of acidic oxides. These arise mostly from metallic elements. When basic oxides, such as magnesium oxide (\(\text{MgO}\)), interact with water, they form alkaline solutions:

• \(\text{MgO + H}_2\text{O} \rightarrow \text{Mg(OH)}_2\)

These basic oxides are known to react with acids, resulting in salt and water. For example, a typical reaction involves calcium oxide:

• \(\text{CaO + HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O}\)

Most common basic oxides come from metals belonging to groups 1 and 2 of the periodic table. These elements form strong bases which are widely used in neutralizing acidic waste products in various industrial processes.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, are transformed into different substances, known as products. This transformation involves rearrangements of atoms. Thermal decomposition, a kind of chemical reaction, occurs when heat is applied to a compound, breaking it down into two or more products.In this type of reaction, the application of heat provides the energy necessary to break chemical bonds, a significant step that leads to the formation of simpler molecules or elements:
1. Compounds such as calcium carbonate (\(\text{CaCO}_3\)) decompose into calcium oxide and carbon dioxide when heated.2. Thermal decomposition is an endothermic reaction, meaning it requires continuous energy input.Understanding the different types of chemical reactions not only explains changes we observe in our environment but also forms the basis for industrial processes like the extraction of metals from ores and the production of gases from various chemical compounds.