11th Class Chemistry Redox Reactions Question Bank 11th CBSE Chemistry Redox Reactions

  • question_answer   Is it possible to store: (i) Copper sulphate solution in a zinc vessel? (ii) Copper sulphate solution in a silver vessel? (iii) Copper sulphate solution in a gold vessel? Given: \[E{{{}^\circ }_{C{{u}^{2+}},\,Cu}}=+0.34\,V;\]\[E{{{}^\circ }_{A{{g}^{+}},\,Ag}}=+0.80\,V\] and\[E{}^\circ {{\,}_{A{{u}^{3+}},\,Au}}=+\,1.50\,V\].

    Answer:

                    (i) We cannot place \[CuS{{O}_{4}}\] solution in a zinc vessel, if the following redox reaction occurs: \[Zn+CuS{{O}_{4}}\xrightarrow{{}}\,ZnS{{O}_{4}}+Cu\] or\[Zn+C{{u}^{2+}}\xrightarrow{\,}\,Z{{n}^{2+}}+Cu\] By convention, the cell may be represented as \[Zn|Z{{n}^{2+}}||C{{u}^{2+}}|Cu\] \[\therefore \]  \[E{{{}^\circ }_{cell}}=E{{{}^\circ }_{C{{u}^{2+}},Cu}}-E{{{}^\circ }_{Z{{n}^{2+}},Zn}}\]   \[=0.34-(-0.76)=+1.10\,V\] Since EMF comes out to be positive, therefore, \[CuS{{O}_{4}}\] reacts with zinc. In other words, \[CuS{{O}_{4}}\] solution cannot be stored in a zinc vessel. (ii) We cannot store \[CuS{{O}_{4}}\] solution in a silver vessel if the following redox reaction occurs: \[2\,Ag\,+C{{u}^{2+}}\xrightarrow{\,}\,2\,A{{g}^{+}}\,+Cu\] By convention, the cell of the above redox reaction may be represented as \[Ag|A{{g}^{+}}||C{{u}^{2+}}|\,Cu\]and\[E{}^\circ {{\,}_{cell}}\,=E{{{}^\circ }_{C{{u}^{2+}},\,Cu}}-E{{{}^\circ }_{A{{g}^{+}},\,Ag}}\] \[=0.34-0.80=-0.56\,V\] Since the EMF of the cell is ?ve, therefore, \[CuS{{O}_{4}}\] does not react with silver. In other words, \[CuS{{O}_{4}}\] solution can be stored in a silver vessel. (iii) We cannot store \[CuS{{O}_{4}}\] solution in a gold vessel if the following redox reaction occurs: \[2\,Au+3\,C{{u}^{2+}}\xrightarrow{\,}\,2\,A{{u}^{3+}}+3\,Cu\] The cell corresponding to the above redox reaction may be represented as \[Au|A{{u}^{3+}}||C{{u}^{2+}}|Cu\] and\[E{}^\circ {{\,}_{cell}}\,=E{{{}^\circ }_{C{{u}^{2+}},\,Cu}}-E{{{}^\circ }_{A{{u}^{3+}},\,Au}}\]\[=0.34-1.50=-1.26\,\text{V}\] Since the EMF of the above cell reaction is ? ve, therefore, \[CuS{{O}_{4}}\] solution does not react with gold. In other words, \[CuS{{O}_{4}}\] solution can be stored in a gold vessel.


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