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Given E_(Zn^(+2)|Zn)^(@)=-0.76V K_(f)[Cu(NH_(3))_(4)]^(+2)=4xx10^(11) E_(Cu^(+2)|Cu)^(@)=0.34V Answer the following. Q. When 1 mole NH_(3) added to cathode compartment than emf of cell is (at 298 K)

Answer»

0.81 V
1.91 V
1.1 V
0.72 V

Solution :`undersetunderset(X)(0.2)(CU^(+2))+undersetunderset(1-0.8)(1)(4NH_(3))hArrundersetunderset(0.2)(0)([Cu(CH_(3))_(4)]^(+2))`
`K_(F)=4.0xx10^(11)=(0.2)/(x xx(0.2)^(4))=(1)/(x xx(0.2)^(3))`
`x=(10^(-11))/((0.2)^(3)xx4)`
`x=3.125xx10^(-10)`
`[Cu^(+2)]=3.125xx10^(-10)`
`E_(cell)=0.75+0.34-(0.0591)/(2)log((2)/(3.125xx10^(-10))`
`=1.1-(0.0591)/(2)(10-0.194)=1.1-0.29=0.81"volt"`


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