Hydrogen Peroxide — Revision Notes

⚡ 30-Second Revision

Formula: — $H_2O_2$
Oxidation State of O: — 1
Structure: — Non-planar, 'open book' structure. Dihedral angle (gas) $approx 111.5^circ$, (solid) $approx 90.2^circ$.
Stability: — Thermodynamically unstable, decomposes to $H_2O + O_2$.
Decomposition: — $2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$. Accelerated by light, heat, metal ions ($Fe^{2+}$), rough surfaces.
Storage: — Dark, wax-lined bottles with stabilizers (urea, acetanilide).
Redox Nature: — Both oxidizing and reducing agent.

- Oxidizing Agent (acidic): $H_2O_2 + 2H^+ + 2e^- \rightarrow 2H_2O$ - Oxidizing Agent (basic): $H_2O_2 + 2e^- \rightarrow 2OH^-$ - Reducing Agent (acidic): $H_2O_2 \rightarrow O_2 + 2H^+ + 2e^-$ - Reducing Agent (basic): $H_2O_2 + 2OH^- \rightarrow O_2 + 2H_2O + 2e^-$

Preparation (Industrial): — Auto-oxidation of 2-ethylanthraquinol.
Preparation (Lab): — $BaO_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O_2$
Uses: — Bleaching, antiseptic, rocket fuel oxidizer.

2-Minute Revision

Hydrogen peroxide ($H_2O_2$) is a crucial compound with oxygen in an unusual -1 oxidation state, giving it a dual redox nature. It's thermodynamically unstable, decomposing into water and oxygen, a process catalyzed by light, heat, and metal ions.

This instability necessitates storage in dark, stabilized containers. Structurally, it's non-planar, resembling an 'open book,' with a dihedral angle of about $111.5^circ$ in the gas phase. Industrially, it's primarily produced via the auto-oxidation of 2-ethylanthraquinol.

As an oxidizing agent, it reduces to $H_2O$ (acidic) or $OH^-$ (basic). As a reducing agent, it oxidizes to $O_2$ (acidic or basic). Key applications include bleaching textiles and paper, acting as an antiseptic, and serving as a rocket fuel oxidizer.

Remember its unique properties, especially its redox behavior and decomposition, are frequently tested.

5-Minute Revision

Hydrogen peroxide ($H_2O_2$) is a pale blue, viscous liquid, often used in aqueous solutions. Its defining characteristic is the O-O single bond, which makes it thermodynamically unstable and prone to decomposition into water and oxygen ($2H_2O_2 \rightarrow 2H_2O + O_2$).

This decomposition is accelerated by light, heat, and catalytic impurities like metal ions ($Fe^{2+}$). Therefore, it's stored in dark, plastic bottles with stabilizers like urea. The oxygen in $H_2O_2$ is in the -1 oxidation state, enabling it to act as both an oxidizing and reducing agent.

As an oxidizing agent, it gets reduced to $H_2O$ in acidic medium ($H_2O_2 + 2H^+ + 2e^- \rightarrow 2H_2O$) and to $OH^-$ in basic medium ($H_2O_2 + 2e^- \rightarrow 2OH^-$). For example, it oxidizes $Fe^{2+}$ to $Fe^{3+}$.

As a reducing agent, it gets oxidized to $O_2$ in both acidic and basic media ($H_2O_2 \rightarrow O_2 + 2H^+ + 2e^-$). A classic example is its reaction with $KMnO_4$, where it reduces $MnO_4^-$ to $Mn^{2+}$.

Its structure is non-planar, often described as an 'open book,' with a dihedral angle of approximately $111.5^circ$ in the gas phase. Industrially, the most important preparation method is the auto-oxidation of 2-ethylanthraquinol, a cyclic process.

Laboratory preparation often involves treating barium peroxide with dilute sulfuric acid. Its uses are diverse, including as a powerful bleaching agent for paper and textiles, an antiseptic for wounds, and an oxidizer in rocket propulsion.

Focus on balancing redox reactions and understanding the factors affecting its stability for NEET.

Prelims Revision Notes

1
Formula & Oxidation State: — $H_2O_2$. Oxygen is in -1 oxidation state.
2
Structure: — Non-planar, 'open book' structure. Two H-O-O planes. Dihedral angle: $approx 111.5^circ$ (gas phase), $approx 90.2^circ$ (solid phase). O-O bond length $147.5,\text{pm}$.
3
Physical Properties: — Pale blue (pure), colorless (dilute solution), syrupy liquid, denser than water, miscible with water, high dielectric constant.
4
Stability & Decomposition: — Thermodynamically unstable. Decomposes exothermically: $2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$.

* Accelerated by: Light (UV), heat, rough surfaces, metal ions ($Fe^{2+}$, $Cu^{2+}$, $Mn^{2+}$), enzymes (catalase). * Storage: Dark-colored, wax-lined plastic bottles. Stabilizers (urea, acetanilide, sodium stannate) are added.

1
Redox Properties:

* Oxidizing Agent (Oxygen from -1 to -2): * Acidic medium: $H_2O_2 + 2H^+ + 2e^- \rightarrow 2H_2O$ * Basic medium: $H_2O_2 + 2e^- \rightarrow 2OH^-$ * Examples: $2Fe^{2+} + H_2O_2 + 2H^+ \rightarrow 2Fe^{3+} + 2H_2O$; $PbS + 4H_2O_2 \rightarrow PbSO_4 + 4H_2O$ (restoration of old oil paintings).

* Reducing Agent (Oxygen from -1 to 0): * Acidic medium: $H_2O_2 \rightarrow O_2 + 2H^+ + 2e^-$ * Basic medium: $H_2O_2 + 2OH^- \rightarrow O_2 + 2H_2O + 2e^-$ * Examples: $2KMnO_4 + 5H_2O_2 + 3H_2SO_4 \rightarrow K_2SO_4 + 2MnSO_4 + 8H_2O + 5O_2$; $Ag_2O + H_2O_2 \rightarrow 2Ag + H_2O + O_2$.

1
Preparation Methods:

* Industrial (Anthraquinone Process): Auto-oxidation of 2-ethylanthraquinol by air, followed by catalytic reduction of 2-ethylanthraquinone. Cyclic process. * Laboratory: From barium peroxide ($BaO_2$) with dilute $H_2SO_4$ or $H_3PO_4$: $BaO_2(s) + H_2SO_4(aq) \rightarrow BaSO_4(s) + H_2O_2(aq)$.

1
Uses: — Antiseptic, disinfectant, bleaching agent (paper, textiles, hair), rocket fuel oxidizer, synthesis of peroxides.

Vyyuha Quick Recall

To remember $H_2O_2$ properties: Hydrogen Peroxide Often Decomposes Rapidly.

Hydrogen peroxide
Preparation (Anthraquinone, Barium Peroxide)
Open book structure
Decomposition (light, heat, catalysts)
Redox agent (Oxidizing AND Reducing)