Hydrogen
1.0 Basic Information
2.0 Atomic and Physical Properties of Hydrogen (reference: NCERT)
3.0 Dihydrogen
4.0 Physical Properties
5.0 Chemical Properties
6.0 Uses of Dihydrogen
7.0 Compounds of Hydrogen
8.0 Hard and Soft Water
9.0 Hydrogen Peroxide
10.0 Volume strength of Hydrogen Peroxide
9.2 Chemical Properties
1. Oxidising Property: Hydrogen Peroxide acts as an oxidising agent both in acidic as well as in alkaline medium.
- In acidic medium: $${H_2}{O_2} + 2{H^ + } + 2{e^ - } \to 2{H_2}O;E^\circ = 1.77V\left( {slow} \right)$$
- In basic medium: $${H_2}{O_2} + 2{e^ - } \to 2O{H^ - };E^\circ = 0.87V\left( {fast} \right)$$
Reactions when it acts as Oxidising Agent:
$$\begin{equation} \begin{aligned} \left( i \right)2KI + {H_2}{O_2} \to 2KOH + {I_2} \\ \left( {ii} \right)PbS + 4{H_2}{O_2} \to PbS{O_4} + 2{H_2}O \\ \left( {iii} \right)KN{O_2} + {H_2}{O_2} \to KN{O_3} + {H_2}O \\ \left( {iv} \right)2FeS{O_4} + {H_2}{O_2} + {H_2}S{O_4} \to F{e_2}{(S{O_4})_3} + 2{H_2}O \\ \left( v \right)2{K_4}[Fe\left( {CN{)_6}} \right] + {H_2}{O_2} + {H_2}S{O_4} \to 2{K_3}Fe{(CN)_6} + {K_2}S{O_4} + {H_2}O \\ \left( {vi} \right)2Cr{\left( {OH} \right)_3} + 4NaOH + 3{H_2}{O_2} \to 2N{a_2}Cr{O_4} + 8{H_2}O \\ \left( {vii} \right)Hg + {H_2}{O_2}\mathop \to \limits^{{H_2}S{O_4}} HgO + {H_2}O \\\end{aligned} \end{equation} $$
2. Reducing Property: In the presence of strong oxidising agents, Hydrogen Peroxide behaves as a Reducing Agent in both the medium.
Reducing action in Acidic Medium:
$$\begin{equation} \begin{aligned} \left( i \right){H_2}{O_2} + {O_3} \to {H_2}O + 2{O_2} \\ \left( {ii} \right){H_2}{O_2} + C{l_2} \to 2HCl + {O_2} \\ \left( {iii} \right){H_2}{O_2} + NaOCl \to NaCl + {H_2}O + {O_2} \\ \left( {iv} \right)2{K_3}[Fe\left( {CN{)_6}} \right] + 2KOH + {H_2}{O_2} \to 2{K_4}(Fe\left( {CN{)_6}} \right) + 2{H_2}O + {O_2} \\ \left( v \right)4{H_2}{O_2} + {K_2}C{r_2}{O_7} + 4{H_2}S{O_4} \to {K_2}S{O_4} + 2Cr{O_5} + 5{H_2}O \\\end{aligned} \end{equation} $$
3. Acidic Property: ${H_2}{O_2}$ is a weak acid (${K_a} = 1.55 \times {10^{ - 12}}$). It has two ionisable hydrogen atoms. It forms two series of salts.
4. Decomposition: ${H_2}{O_2}$ decomposes slowly on exposure to light. $$2{H_2}{O_2}\left( l \right) \to 2{H_2}O\left( l \right) + {O_2}\left( g \right)$$ In the presence of metal surfaces or traces of alkali (present in glass containers), the above reaction is catalysed. It is, therefore, stored in wax-lined glass or plastic vessels in dark. Urea can be added as a stabiliser. It is kept away from dust because dust can induce explosive decomposition of the compound.
5. Addition Reaction: Hydrogen Peroxide is capable of adding itself to double bond.
6. As Bleaching Agent: It acts as a bleaching agent for delicate materials like wool, silk, ivory. It bleaches hair to golden yellow colour. The bleaching action of ${H_2}{O_2}$ is due to its oxidising character. $${H_2}{O_2} \to {H_2} + \left[ O \right]$$
