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Uses of Standard Hydrogen Electrodes

The standard hydrogen electrode represents the zero point on a scale of electrode potentials used by chemists to understand redox (i.e., relating to oxidation-reduction) reactions. It is basically a gas electrode. Hydrogen gas is injected into a glass cell that contains a platinum electrode (the platinum does not take part in any reactions). The gas electrode is inserted into a dilute acid solution (1 mol dm-3 H+ (aq)) with which the hydrogen gas reacts. The standard hydrogen electrode is kept under standard conditions of temperature (298 degrees Kelvin) and pressure (1 atmosphere). Standard hydrogen electrodes have many applications.

  1. Standard

    • The IUPAC (International Union of Pure and Applied Chemistry) lists the standard hydrogen electrode as the universal reference electrode, which is considered to have a standard electrode potential of zero under standard conditions at all temperatures. The standard hydrogen electrode cell is connected to another cell with a different type of electrode in order to measure the potential of that other electrode. The cells are connected by a wire to which a voltmeter (an instrument for measuring in volts the differences in potential between different points of an electrical circuit) is also attached. A salt bridge between the two cells completes the circuit. The standard hydrogen electrode is connected as the left-hand electrode.

    To Detect Electrode Potential of a Tested Material

    • The standard hydrogen electrode is considered to have a potential of zero, so the standard electrode potential of the tested material is considered to be equal to that of the entire cell. If it is negative, the tested electrode has a greater tendency to lose electrons than hydrogen. If it is positive, the tested electrode is less ready to lose electrons than hydrogen, and in fact has a greater tendency to gain electrons than hydrogen. This is rarely done in practice, as the hydrogen electrode is difficult to use.

    Electrochemical Series

    • The standard electrode potentials of different materials can be compared. They are placed in order in the electrochemical series, from the most negative to the most positive. Materials that are very negative are good reducing agents, while the most positive materials are good oxidizing agents. The direction of a redox reaction between any two materials in the series can be predicted by comparing their standard electrode potentials. The more negative material in the pair will lose electrons (be oxidized) while the more positive material will gain them (be reduced). The difference must be more than 0.3 V for a reaction to occur under normal conditions, however.

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