Question

2. Calculate the standard emf of a cell that uses the Mg/Mg+2 and Cu/Cu+2 half-cell reactions at 25ºC. Write the equation for the cell reaction that occurs under standard-state conditions. (10 points)

Answer 1

Answer:

2.71 V

Explanation:

Usually in the cell notation, the left side shows oxidation. So,  

Oxidation half reaction:

$Mg_{(s)}\rightarrow Mg^{2+}_{(aq)}+2e^-$    $E^o_{ox}=-E^o_{red}=-(-2.37\ V)=2.37\ V$

Reduction half reaction:

$Cu^{2+}_{(aq)}+2e^-\rightarrow Cu_{(s)}$    $E^o_{red}=0.34\ V$

Overall reaction:

$Mg_{(s)}+Cu^{2+}_{(aq)}\rightarrow Mg^{2+}_{(aq)}+Cu_{(s)}$

$E^o_{cell}=E^o_{ox}+E^o_{red}= (2.37+0.34)\ V=2.71\ V$