Chemistry

Problem

Four standard half-reactions are listed below (298 K). Fe

^{3+}

+ e

^{-}

→ Fe

^{2+}

E^{\circ}=+0.77\,\text{V}

^{2+}

+ 2 e

^{-}

→ Pb(s)

E^{\circ}=-0.13\,\text{V}

^{2+}

+ 2 e

^{-}

→ Zn(s)

E^{\circ}=-0.76\,\text{V}

^{3+}

+ 3 e

^{-}

→ Al(s)

E^{\circ}=-1.66\,\text{V}

Using any two of these half-reactions, a student wishes to build a galvanic cell. Which pairing will produce the largest positive

E^{\circ}_{\text{cell}}

, and what is its value? a)

\text{Fe}^{3+}/\text{Fe}^{2+}

cathode and

\text{Zn}^{2+}/\text{Zn}

anode;

E^{\circ}_{\text{cell}}=+1.53\,\text{V}

\text{Fe}^{3+}/\text{Fe}^{2+}

cathode and

\text{Al}^{3+}/\text{Al}

anode;

E^{\circ}_{\text{cell}}=+2.43\,\text{V}

\text{Zn}^{2+}/\text{Zn}

cathode and

\text{Al}^{3+}/\text{Al}

anode;

E^{\circ}_{\text{cell}}=+0.90\,\text{V}

\text{Fe}^{3+}/\text{Fe}^{2+}

cathode and

\text{Al}^{3+}/\text{Al}

anode;

E^{\circ}_{\text{cell}}=+3.97\,\text{V}