Question

The standard reduction potentials of the following half-reactions are given in Appendix E in the textbook:

Ag+(aq)+e−→Ag(s)= .799
Cu2+(aq)+2e−→Cu(s)= .337
Ni2+(aq)+2e−→Ni(s)= -.28
Cr3+(aq)+3e−→Cr(s). = -.74
1. Determine which combination of these half-cell reactions leads to the cell reaction with the largest positive cell emf.
1st and 2nd,
1st and 3rd,
1st and 4th,
2nd and 3rd,
3rd and 4th.
It isn't the first or last one because I have gotten it wrong twice.
2. Calculate the value of this emf.
3. Then determine which combination is the smallest and calculate the emf.

Answer 1

For 1: The largest positive cell potential is of cell having 1st and 4th half reactions.

For 2: The standard electrode potential of the cell is 1.539 V

For 3: The smallest positive cell potential is of cell having 3rd and 4th half reactions. The standard electrode potential of the cell is 0.46 V

Step-by-step explanation:

The substance having highest positive
`E^o` potential will always get reduced and will undergo reduction reaction.

We are given:

`Ag^++(aq.)+e^-\rightarrow Ag(s);E^o_(Ag^+/Ag)=0.799V\\\\Cu^(2+)+(aq.)+2e^-\rightarrow Cu(s);E^o_(Cu^(2+)/Cu)=0.337V\\\\Ni^(2+)(aq.)+2e^-\rightarrow Ni(s);E^o_(Ni^(2+)/Ni)=-0.28V\\\\Cr^(3+)(aq.)+3e^-\rightarrow Cr(s);E^o_(Cr^(3+)/Cr)=-0.74V`

Substance getting oxidized always act as anode and the one getting reduced always act as cathode.

To calculate the
`E^o_(cell)` of the reaction, we use the equation:

`E^o_(cell)=E^o_(cathode)-E^o_(anode)`

• Cell having 1st and 2nd half reactions:

Silver has higher electrode potential. So, this will undergo reduction reaction and act as anode. Copper will undergo oxidation reaction and act as cathode.

`E^o_(cell)=0.799-0.337=0.462V`

• Cell having 1st and 3rd half reactions:

Silver has higher electrode potential. So, this will undergo reduction reaction and act as anode. Nickel will undergo oxidation reaction and act as cathode.

`E^o_(cell)=0.799-(-0.28)=1.079V`

• Cell having 1st and 4th half reactions:

Silver has higher electrode potential. So, this will undergo reduction reaction and act as anode. Chromium will undergo oxidation reaction and act as cathode.

`E^o_(cell)=0.799-(-0.74)=1.539V`

• Cell having 2nd and 3rd half reactions:

Copper has higher electrode potential. So, this will undergo reduction reaction and act as anode. Nickel will undergo oxidation reaction and act as cathode.

`E^o_(cell)=0.337-(-0.28)=0.617V`

• Cell having 3rd and 4th half reactions:

Nickel has higher electrode potential. So, this will undergo reduction reaction and act as anode. Chromium will undergo oxidation reaction and act as cathode.

`E^o_(cell)=-0.28-(-0.74)=0.46V`

Hence,

For 1: The largest positive cell potential is of cell having 1st and 4th half reactions.

For 2: The standard electrode potential of the cell is 1.539 V

For 3: The smallest positive cell potential is of cell having 3rd and 4th half reactions. The standard electrode potential of the cell is 0.46 V