Use the principles of electrochemistry to answer these questions:
(a) Why is a salt bridge connecting two compartments of a galvanic cell necessary for the operation of the cell?
(b) When an iron nail is placed in hydrochloric acid a reaction occurs but no reaction occurs when a copper penny is placed in hydrochloric acid. Explain.
(c) Describe how molten sodium chloride can be electrolyzed to form pure sodium and pure chlorine.
(d) When molten sodium chloride is replaced with an aqueous solution of sodium chloride, pure sodium is not produced. Explain.