Oxidation and Reduction Questions

Correct Answer

📖 Core Concept

Redox reactions involve the transfer of electrons, leading to changes in oxidation states of reactants. The general equation governing redox reactions can be represented as:

Oxidation: \( \text{Zn} \rightarrow \text{Zn}^{2+} + 2e^- \)

Reduction: \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \)

🧪 Step-by-Step Breakdown

The evaluation of each option determines if they are redox reactions:

• Option A: AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl

No change in oxidation states:

Oxidation State of Al: +3 (both sides)

Oxidation State of Cl: -1 (both sides)

• Option B: 2NaH → 2Na + H₂

Redox Reaction:

Oxidation: \( \text{Na}^{+} \rightarrow \text{Na}^0 \)

Reduction: \( \text{H}^0 \rightarrow \text{H}_2 \)

• Option C: 4Fe + 3O₂ → 2Fe₂O₃

Redox Reaction:

Oxidation: \( \text{Fe}^0 \rightarrow \text{Fe}^{+3} \)

Reduction: \( \text{O}_2^{0} \rightarrow \text{O}^{-2} \)

• Option D: CuSO₄ + Zn → Cu + ZnSO₄

Redox Reaction:

Oxidation: \( \text{Zn}^0 \rightarrow \text{Zn}^{+2} \)

Reduction: \( \text{Cu}^{+2} \rightarrow \text{Cu}^0 \)

🔍 Option Analysis

Options B, C, and D are valid redox reactions as they involve changes in oxidation states, while Option A is an acid-base reaction (no change in oxidation states).

⚡ Mnemonic / Speed-Run

Mnemonic: "LEO says GER" — Lose Electrons Oxidation, Gain Electrons Reduction.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The reaction follows the principles of the reactivity series of metals. Iron displaces copper from copper sulfate solution, indicating that iron is more reactive.

🧪 Step-by-Step Breakdown

In the reaction:

Here, iron (Fe) oxidizes to Fe²⁺ and reduces Cu²⁺ to Cu. Thus:

• Iron acts as a reducing agent.
• The resulting solution of FeSO₄ turns green due to iron ions.
• Copper is less reactive compared to iron.
• This is a redox reaction.

🔍 Option Analysis

• A: Iron is the reducing agent - correct.
• B: The solution turns green - correct.
• C: Copper is a more reactive metal than iron - incorrect.
• D: It is a redox reaction - correct.

⚡ Mnemonic / Speed-Run

Remember, "Higher on the list, easier to displace" for reactivity series of metals.

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

In organic chemistry, an addition reaction involves the addition of one or more atoms or groups to a molecule without the loss of any atom from it.

🧪 Step-by-Step Breakdown

Vegetable oils, composed mainly of unsaturated fatty acids, undergo hydrogenation to form saturated fats. This process is typically represented by the equation: Here, \( \text{C}_n\text{H}_{2n-2} \) represents unsaturated fatty acids and \( \text{C}_n\text{H}_{2n} \) is the resultant saturated fatty acid (vegetable ghee). The nickel catalyst facilitates this addition by breaking the double bonds in the unsaturated hydrocarbons.

🔍 Option Analysis

- **A: Substitution reaction:** Involves the replacement of an atom in a molecule. - **B: Elimination reaction:** Involves the loss of atoms to form a double bond. - **D: Free-radical polymerization:** A process involving the reaction of monomers that form polymers.

⚡ Mnemonic / Speed-Run

Remember: "Addition is for hydrogenation!" to quickly recall that hydrogenation leads to addition reactions.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The reaction follows the principles of redox chemistry, where reducing and oxidizing agents are defined based on electron transfer. Here, N2H4 (hydrazine) undergoes oxidation while H2O2 (hydrogen peroxide) serves as the oxidizing agent.

🧪 Step-by-Step Breakdown

The given reaction:

Analyzing oxidation states:

• Oxidation state of N in N2H4: -2
• Oxidation state of N in N2: 0
• Oxidation state of O in H2O2: -1
• Oxidation state of O in H2O: -2

Change in oxidation states signifies:

• From -2 (N2H4) to 0 (N2): N2H4 is oxidized.
• O in H2O2 goes from -1 to -2: H2O2 is reduced.

Conclusion: N2H4 is acting as the reducing agent.

🔍 Option Analysis

• H2O2: Acts as the oxidizing agent, gaining electrons.
• N2: Product of reduction, not an agent.
• H2O: Also a product, no redox role.

⚡ Mnemonic / Speed-Run

Remember: "OIL RIG" - Oxidation Is Loss, Reduction Is Gain. N2H4 loses electrons, hence it is oxidized.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Oxidation is a chemical process where a substance loses electrons, often increasing its oxidation state. The general reaction can be framed as:

🧪 Step-by-Step Breakdown

In the rusting process, iron (Fe) reacts with oxygen (O₂) and moisture to form iron(III) oxide (Fe₂O₃), commonly known as rust. The process can be outlined in steps:

• Iron gets oxidized to ferrous ions (Fe²⁺):
\[ 4Fe + 3O_2 + 6H_2O \rightarrow 4Fe(OH)_3 \]
• Ferrous ions further oxidize to ferric ions (Fe³⁺):
\[ 4Fe(OH)_3 \rightarrow 2Fe_2O_3 \cdot 3H_2O \]

The final product illustrates a characteristic reddish-brown color indicative of rust.

🔍 Option Analysis

• A: Freezing of water - Physical change, no oxidation.
• B: Dissolving sugar in water - Physical process, no electron transfer.
• D: Boiling of petrol - Physical change, vaporization only.

⚡ Mnemonic / Speed-Run

For oxidation states, remember: "OIL RIG" (Oxidation Is Loss, Reduction Is Gain) to recall the electron transfer processes.

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Chemical weathering encompasses processes that chemically alter minerals and rocks.

🧪 Step-by-Step Breakdown

Key processes of chemical weathering include:

• Solution: Dissolution of minerals in water, e.g., NaCl (s) + H₂O (l) → Na⁺ (aq) + Cl⁻ (aq).
• Hydration: Incorporation of water molecules into mineral structures, resulting in expansion.
• Reduction: Loss of oxygen from minerals, e.g., 4Fe₂O₃ + 12C → 8Fe + 12CO.

In contrast, thawing is merely a phase change of ice melting into water, without chemical alteration of substances.

🔍 Option Analysis

• A: Solution: Involves dissolving minerals, altering their chemical composition.
• B: Hydration: Integrates water into the mineral structure, contributing to chemical changes.
• C: Reduction: Reduces the oxidation state, affecting mineral composition.
• D: Thawing: A physical transformation that does not affect mineral chemistry.

⚡ Mnemonic / Speed-Run

Remember: Chemical changes alter compositions (Solution, Hydration, Reduction), while physical changes reorganize states (such as Thawing).

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The melting points of ionic compounds, predominantly influenced by their lattice energy, dictate their thermal stability. The relationship can be summarized as:

Stronger ionic bonds → Higher melting point.

🧪 Step-by-Step Breakdown

The melting points of the given oxides are:

• Na₂O: 1132°C
• MgO: 2852°C
• Fe₂O₃: 1565°C
• CuO: 1326°C

MgO is an ionic compound with a significant lattice energy resulting from the strong electrostatic forces between Mg²⁺ and O^2- ions. This leads to its high melting point, compared to the other oxides listed.

🔍 Option Analysis

Na₂O, Fe₂O₃, and CuO possess ionic or covalent properties that contribute to lower melting points due to weaker ionic/covalent bonds or lattice structures.

⚡ Mnemonic / Speed-Run

Recall that magnesium (Mg) is in the period where ionic bonds (greater lattice energy) typically yield the highest melting points.

6. Visual Suggestion

📖 Factual Verification & Reference