# Explain why a standard hydrogen electrode is assigned a standard electrode potential of exactly 0.00 V, and outline how this value is used to determine the standard electrode potential of another half-cell.

> IB DP Chemistry Standard Level (2023 syllabus) — R3.2 Electron transfer reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. The standard hydrogen electrode (SHE) is assigned 0.00 V by international convention / definition, not because it has no tendency to react.
2. It acts as a universal reference electrode against which all other half-cell potentials are measured.
3. The unknown half-cell is connected to the SHE under standard conditions (298 K, 100 kPa, 1 mol dm⁻³ solutions), and the voltage (e.m.f.) of the resulting electrochemical cell is measured.
4. Because the SHE contributes 0.00 V, the measured cell voltage equals the standard electrode potential of the unknown half-cell; its sign indicates whether the half-cell acts as the positive (cathode) or negative (anode) terminal relative to the SHE.

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