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 (d) \(+6,+4\) and \(+4\)

Step-by-Step Solution

Answer

The correct answer is (b) +3, -4, and zero.

Step 1: Determine oxidation state in H2C2O4

The total oxidation state of hydrogen is usually +1, and there are two hydrogen atoms, contributing +2. Oxygen usually has an oxidation state of -2, and there are four oxygen atoms, contributing -8. Let the oxidation state of carbon be x for each carbon atom (there are two carbon atoms). The sum of oxidation states should equal zero for neutral compounds.\[ 2(+1) + 2x + 4(-2) = 0\]Simplifying gives:\[ 2 + 2x - 8 = 0 \]\[ 2x - 6 = 0 \]\[ 2x = 6 \]\[ x = +3 \]So the oxidation number of carbon in \(\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4\) is +3.

Step 2: Determine oxidation state in CH4

In \(\mathrm{CH}_4\), hydrogen has an oxidation state of +1, and there are four hydrogen atoms, contributing a total of +4. The oxidation state of carbon is x. Since the compound is neutral, the sum of the oxidation states must be zero:\[ x + 4(+1) = 0 \]\[ x + 4 = 0 \]\[ x = -4 \]Thus, the oxidation number of carbon in \(\mathrm{CH}_4\) is -4.

Step 3: Determine oxidation state in diamond

Diamond is a form of elemental carbon where carbon atoms are bonded to each other in a regular pattern. Since the element is in its elemental form, the oxidation state of the carbon atom in diamond is 0.

Step 4: Compare with answer choices

From the preceding steps, we found the oxidation states: - In \(\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4\), carbon is +3.- In \(\mathrm{CH}_4\), carbon is -4.- In diamond, carbon is 0.Comparing these results to the answer choices, the correct answer is (b) \(+3, -4\) and zero.

Key Concepts

Oxidation State

The oxidation state, also known as oxidation number, is a fundamental concept in chemistry. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. It is a useful tool in determining electron flow in redox reactions.
Oxidation states are assigned based on a set of rules. For example:

• The oxidation state of an element in its natural form, like O₂ or diamond (which is pure carbon), is always 0.
• Fluorine in compounds is always -1, and oxygen is typically assigned -2 in most compounds.
• Hydrogen usually has +1 unless it's paired with more electropositive elements, like metals, where it is -1.

Remember, the overall charge of the compound equals the sum of the oxidation states of all atoms present. In neutral compounds, this sum is zero, which is pivotal for calculating unknown oxidation states.

Organic Compounds

Organic compounds are primarily composed of carbon and hydrogen, often with additional elements such as oxygen, nitrogen, sulfur, and halogens. The structure and arrangement of these atoms define the properties and reactions of the compounds.
In the context of this exercise:

• \(\text{H}_2\text{C}_2\text{O}_4\) (oxalic acid) is an organic compound where two carbon atoms are bonded with each other and to oxygen.
• \(\text{CH}_4\) (methane) is one of the simplest organic compounds, consisting of one carbon atom bonded to four hydrogen atoms. It's a significant component of natural gas.
• Diamond is a form of pure carbon, structured in a robust three-dimensional lattice.

Understanding the bonds in these organic compounds allows us to apply the rules of oxidation states effectively.

Elementary Chemistry Concepts

Elementary chemistry concepts lay the foundation for understanding more complex chemical principles. These basics include understanding atoms, molecules, compounds, and how they interact with each other.
Key elements of elementary chemistry involve:

• Atoms: The basic unit of chemical elements, composed of protons, neutrons, and electrons.
• Molecules: Formed when two or more atoms bond together. The composition determines the chemical properties and reactivity.
• Compounds: Substances formed when atoms of different chemical elements are chemically bonded.
• Chemical Reactions: Processes where substances change into different substances through breaking and forming chemical bonds.

Grasping these concepts is essential because they define the groundwork for more advanced topics like oxidation states, reactions in organic chemistry, and even the behavior of elements and compounds under different conditions. It's this foundational knowledge that enables deeper understanding and problem-solving in chemistry.