question_answer 1)

Write chemical reactions to justify that hydrogen peroxide can function as an oxidising as well as a reducing agent.

Answer:

\[{{H}_{2}}{{O}_{2}}\] acts as an oxidising as well as a reducing agent both in acidic and basic mediums. This is justified by following reactions: Oxidising agent Acidic medium: (a) Acidified ferrous sulphate is oxidised to ferric sulphate. \[2FeS{{O}_{4}}+{{H}_{2}}S{{O}_{4}}+{{H}_{2}}{{O}_{2}}\to F{{e}_{2}}{{(S{{O}_{4}})}_{3}}+2{{H}_{2}}O\] (b) In acidic solution, mercury is oxidised. \[Hg+{{H}_{2}}{{O}_{2}}\xrightarrow{{{H}_{2}}S{{O}_{4}}}HgO+{{H}_{2}}O\] (c) A solution of acidified \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]is oxidised to blue peroxide of chromium\[(Cr{{O}_{5}})\]. \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}+4{{H}_{2}}{{O}_{2}}\to 2Cr{{O}_{5}}+{{K}_{2}}S{{O}_{4}}+5{{H}_{2}}O\]Alkaline medium : (a) Chromium hydroxide is oxidised by \[{{H}_{2}}{{O}_{2}}\]in presence of \[\text{NaOH}\] into \[\text{N}{{\text{a}}_{2}}Cr{{O}_{4}}.\] \[2Cr{{(OH)}_{3}}+4NaOH+3{{H}_{2}}{{O}_{2}}\to 2N{{a}_{2}}Cr{{O}_{4}}+8{{H}_{2}}O\](b) \[MnS{{O}_{4}}\] is oxidised to Mn02. \[MnS{{O}_{4}}+2NaOH+{{H}_{2}}{{O}_{2}}\to Mn{{O}_{2}}+N{{a}_{2}}S{{O}_{4}}+2{{H}_{2}}O\] (c) HCHO is oxidised to HCOOH \[HCHO+{{H}_{2}}{{O}_{2}}\to HCOOH+{{H}_{2}}O\] Reducing agent Acidic medium: (a) \[Mn{{O}_{2}}\] in acidic medium is reduced to \[MnS{{O}_{4}}\]. \[Mn{{O}_{2}}+{{H}_{2}}S{{O}_{4}}+{{H}_{2}}{{O}_{2}}\to MnS{{O}_{4}}+2{{H}_{2}}O+{{O}_{2}}\](b) Red lead in presence of HN03 is reduced to plumbous salt. \[P{{b}_{3}}{{O}_{4}}+6HNN{{O}_{3}}+{{H}_{2}}{{O}_{2}}\to 3Pb{{(N{{O}_{3}})}_{2}}+4{{H}_{2}}O+{{O}_{2}}\](c) It reduces acidified\[KMn{{O}_{4}}\]. \[2KMn{{O}_{4}}+3{{H}_{2}}S{{O}_{4}}+5{{H}_{2}}{{O}_{2}}\to {{K}_{2}}S{{O}_{4}}\] \[+2MnS{{O}_{4}}+8{{H}_{2}}O+5{{O}_{2}}\] Alkaline medium: (a)Potassium ferricyanide is reduced to ferrocyanide in presence of\[KOH+{{H}_{2}}{{O}_{2}}\]. \[2{{K}_{3}}Fe{{(CN)}_{6}}+2KOH+{{H}_{2}}{{O}_{2}}\to 2{{K}_{4}}Fe{{(CN)}_{6}}+2{{H}_{2}}O+{{O}_{2}}\](b) Iodine is reduced. \[{{I}_{2}}+2KOH+{{H}_{2}}{{O}_{2}}\to 2KI+2{{H}_{2}}O+{{O}_{2}}\]