Consider the skeletal equation Mn(s) + Ti2+(aq) → Mn2+(aq) + Ti(s). What is the proper shorthand notation (cell diagram) for this reaction?

• A. Mn(s) | Mn2+(aq) || Ti2+(aq) | Ti(s)
• B. Ti(s) | Ti2+(aq) || Mn2+(aq) | Mn(s)
• C. Ti2+(aq) | Ti(s) || Mn(s) | Mn2+(aq)
• D. Mn2+(aq) | Mn(s) || Ti(s) | Ti2+(aq)

Answer: (A)

In shorthand notation, the anode (where oxidation happens) is on the left and the cathode (where reduction happens) is on the right. The solid electrode sits at the boundary with its ion product in solution next to it. For the given reaction, manganese metal is oxidized to Mn2+, so Mn(s) and Mn2+(aq) belong on the left. Titanium(II) ions are reduced to titanium metal, so Ti2+(aq) and Ti(s) belong on the right. The two compartments are separated by a salt bridge, shown as a double line. Therefore the proper diagram is Mn(s) | Mn2+(aq) || Ti2+(aq) | Ti(s).