Problem 25 - A Complete Resource Book in Chemistry for JEE Main

Question

Oxidation numbers of carbon in \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}, \mathrm{CH}_{4}\) and diamond respectively are (a) \(+3,4\) and \(+4\) (b) \(+3,-4\) and zero (c) \(+6,+4\) and zero

Step-by-Step Solution

Answer

Option (b) is correct: +3, -4, and zero.

Step 1: Understand the Concept of Oxidation Numbers

Oxidation numbers are a theoretical concept used to determine how many electrons are lost or gained by an atom in a compound. It helps in tracking electron flow in redox reactions.

Step 2: Calculate Oxidation Numbers for H₂C₂O₄

In oxalic acid (H₂C₂O₄), the typical oxidation number for hydrogen is +1 and for oxygen is -2. The sum of the oxidation numbers in a neutral compound is zero. Let the oxidation number of carbon be x. The equation becomes:\[2(+1) + 2x + 4(-2) = 0\]\[2 + 2x - 8 = 0\]\[2x = +6\]\[x = +3\]Thus, the oxidation number of carbon in H₂C₂O₄ is +3.

Step 3: Calculate Oxidation Numbers for CH₄

In methane (CH₄), the oxidation number of hydrogen is +1. Let the oxidation number of carbon be x. The equation is:\[x + 4(+1) = 0\]\[x + 4 = 0\]\[x = -4\]Thus, the oxidation number of carbon in CH₄ is -4.

Step 4: Determine Oxidation Number for Diamond

Diamond is a form of carbon where carbon atoms are bonded to each other in a 3D lattice. Since the bonds are all between the same type of atom, the oxidation number of carbon in diamond is zero.

Step 5: Compare with the Given Options

The calculated oxidation numbers are +3 for H₂C₂O₄, -4 for CH₄, and 0 for diamond. Compare this with the given options to find the correct answer.

Key Concepts

Oxidation number calculation

Oxidation numbers serve as a tool for tracking electrons in a chemical reaction. They provide insight into electron density changes, shedding light on oxidation and reduction events. To determine the oxidation number of an atom in a compound, remember these key rules:

• For elements in their pure state (like O₂ or diamond), the oxidation number is typically zero.
• Hydrogen generally has an oxidation number of +1 when bonded to nonmetals.
• Oxygen usually has an oxidation number of -2 in compounds, except in peroxides.
• In a neutral molecule, the sum of the oxidation numbers of all atoms must be zero. In ions, it equals the charge of the ion.

By following these rules, you can assign oxidation numbers and track electron transfers in chemical compounds. For example, in oxalic acid (H₂C₂O₄), assign oxidation numbers systematically to solve for carbon's oxidation state.

Redox reactions

Redox reactions are a type of chemical reaction involving the transfer of electrons between two species. They are characterized by two concurrent processes: oxidation (loss of electrons) and reduction (gain of electrons). Understanding these reactions aids in comprehending how energy is transferred in chemical processes.
Here’s a simple breakdown of what these terms mean:

• **Oxidation:** An increase in oxidation number due to loss of electrons.
• **Reduction:** A decrease in oxidation number, indicating a gain of electrons.

A classic example is the reaction between hydrogen and fluorine, where hydrogen is oxidized, and fluorine is reduced.
Redox reactions are fundamental in both biological systems (e.g., cellular respiration) and industrial processes (e.g., corrosion prevention), playing a crucial role in energy conversion and material synthesis.

Carbon compounds

Carbon compounds form the core of organic chemistry due to carbon's unique ability to form stable bonds with many elements, including itself. This property allows carbon to create long chains and complex structures like rings, making it an essential building block for an immense variety of molecules.
Different carbon compounds exhibit varied oxidation numbers, influencing their chemical reactivity and stability. For instance, in methane (CH₄), carbon is bonded to four hydrogen atoms with an oxidation number of -4, signifying it is in a fully reduced state. In contrast, in dioxide compounds or carbonates, carbon is often more oxidized.
Understanding how carbon's oxidation state changes in different compounds is vital for predicting chemical behavior and reactions. This knowledge is particularly important in fields such as organic synthesis, environmental chemistry, and the development of energy solutions like fuels and batteries.