The standard hydrogen electrode consists of hydrogen gas at 1 atmosphere bubbled over
- A. a zinc rod in zinc sulphate solution
- B. platinised platinum foil dipping in 1 molar hydrogen ion solution
- C. a copper rod in copper sulphate solution
- D. a carbon rod in pure water
Explanation
Platinum is used because it is chemically inert and does not itself take part in the reaction, while the finely divided platinum black coating provides a large surface that catalyses the equilibrium between hydrogen gas and hydrogen ions. The solution must be exactly 1 molar in hydrogen ions and the temperature 298 K for the potential to be standard. Any reactive metal would corrode and destroy the reference.