11th Class Chemistry Redox Reactions

  • question_answer 27) Consider the reactions: (a) \[{{H}_{3}}P{{O}_{2}}(aq)+4AgN{{O}_{3}}(aq)+2{{H}_{2}}O(l)\] \[\to \,{{H}_{3}}P{{O}_{4}}(aq)+4Ag(s)+4HN{{O}_{3}}(aq)\] (b) \[{{H}_{3}}P{{O}_{2}}(aq)+2CuS{{O}_{4}}(aq)+2{{H}_{2}}O(l)\] \[\to {{H}_{3}}P{{O}_{4}}(aq)+2Cu(s)+{{H}_{2}}S{{O}_{4}}(aq)\] (c) \[{{C}_{6}}{{H}_{5}}CHO(l)+2{{[Ag{{(N{{H}_{3}})}_{2}}]}^{+}}(aq)+3O{{H}^{-}}\to \]\[{{C}_{6}}{{H}_{5}}CO{{O}^{-}}(aq)+2Ag(s)+4N{{H}_{3}}(aq)+2{{H}_{2}}O(l)\](d) \[{{C}_{6}}{{H}_{5}}CHO(l)+2C{{u}^{2+}}(aq)+\underset{No\,change\,observed.}{\mathop{5O{{H}^{-}}(aq)\to }}\,\] What inference do you draw about the behaviour of and \[C{{u}^{2+}}\]from these reactions?  

    Answer:

    (a) \[{{H}_{3}}P{{O}_{2}}(aq)+4\overset{+1}{\mathop{AgN{{O}_{3}}}}\,(aq)+2{{H}_{2}}O(l)\to \]\[{{H}_{3}}P{{O}_{4}}(aq)+4Ag(s)+4HN{{O}_{3}}(aq)\] \[A{{g}^{+}}\]ion is reduced to , thus \[Ag\] acts as an oxidising agent, it oxidises \[{{H}_{3}}P{{O}_{2}}\] to \[{{H}_{3}}P{{O}_{4}}\] (b) \[{{H}_{3}}P{{O}_{2}}(aq)+2\overset{2+}{\mathop{CuS{{O}_{4}}}}\,(aq)+2{{H}_{2}}O(l)\to \]\[{{H}_{3}}P{{O}_{4}}(aq)+2\overset{0}{\mathop{Cu}}\,(s)+{{H}_{2}}S{{O}_{4}}(aq)\] \[C{{u}^{2+}}\]ion is reduced to\[Cu(s)\], thus \[C{{u}^{2+}}\] acts as oxidising agent, it oxidises \[{{H}_{3}}P{{O}_{2}}\] to \[{{H}_{3}}P{{O}_{4}}\]. (c)\[{{C}_{6}}{{H}_{5}}CHO(l)+2{{[\overset{+1}{\mathop{Ag}}\,{{(N{{H}_{3}})}_{2}}]}^{+}}(aq)+3O{{H}^{-}}(aq)\]\[\to {{C}_{6}}{{H}_{5}}CO{{O}^{-}}+2Ag(s)+4N{{H}_{3}}(aq)+2{{H}_{2}}O(l)\] In above reaction, \[A{{g}^{+}}\] ion is reduced to \[Ag(s)\]thus it acts as an oxidising agent; it oxidises \[{{C}_{6}}{{H}_{5}}CHO\]to\[{{C}_{6}}{{H}_{5}}CO{{O}^{-}}(aq).\]. (d) \[{{C}_{6}}{{H}_{5}}CHO(l)+2C{{u}^{2+}}+5O{{H}^{-}}\to \] No change. It is not a redox reaction.  


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