Question

A standard galvanic cell is constructed so that the overall cell reaction is as given below where M is an unknown metal. 2 Al3+(aq) + 3 M(s) 3 M2+(aq) + 2 Al(s) If ΔG° = -411 kJ for the overall cell reaction, identify the metal used to construct the standard cell.

Answer 1

magnesium metal

Step-by-step explanation:

According to the redox reaction equation, six electrons were transferred hence n=6 and F= Faraday's constant 96500C. ∆G° is given hence E°cell can easily be calculated as follows:

From ∆G°= -nFE°cell

E°cell= -∆G°/nF= -(-411×10^3/96500×6)

E°cell= 0.7098V

But for Al3+(aq)/Al(s) half cell, E°= -1.66V from standard table of reduction potentials.

E°cell= E°cathode- E°anode but Al3+(aq)/Al(s) half cell is the cathode

Hence

E°anode=E°cathode - E°cell

E°anode= -1.66-0.7098= -2.37V

This is the reduction potential of Mg hence the anode material was magnesium metal