Question

(a) What is a standard reduction potential? (b) What is the standard reduction potential of a standard hydrogen electrode?

Short answer

The standard reduction potential is a measure of a chemical species' tendency to undergo reduction, which is the process of gaining electrons. It represents the voltage associated with a reduction reaction under standard conditions (298 K, 1 atmosphere, and 1.0 M concentration). The standard reduction potential is typically measured against a reference electrode, the Standard Hydrogen Electrode (SHE). The SHE consists of a platinum electrode in contact with hydrogen gas at a pressure of 1 atmosphere and is immersed in a solution containing hydrogen ions (H+) with a concentration of 1.0 M. The standard reduction potential of the SHE is defined to be exactly 0 volts (0 V) under standard conditions, serving as a reference point to compare and measure the reduction potentials of other half-cell reactions.

Step-by-step solution

(Define Standard Reduction Potential)

Standard reduction potential is a measure of the tendency of a chemical species to undergo reduction, which is the process of gaining electrons. It is a value that represents the voltage (or electric potential) associated with a reduction reaction when it occurs under standard conditions, which include a temperature of 298 K (25°C), a pressure of 1 atmosphere, and a concentration of 1.0 M for the involved chemical species. The standard reduction potentials are typically measured against a reference electrode, which is the standard hydrogen electrode.

(Explain Standard Hydrogen Electrode)

The Standard Hydrogen Electrode (SHE) is a reference electrode used in electrochemical measurements and acts as a standard for measuring the reduction potential of other species. It consists of a platinum electrode that is in contact with hydrogen gas at a pressure of 1 atmosphere and is also immersed in a solution containing hydrogen ions (H+) with a concentration of 1.0 M.

(Standard Reduction Potential of Standard Hydrogen Electrode)

The standard reduction potential of the Standard Hydrogen Electrode is defined to be exactly 0 volts (0 V) under standard conditions. This is because the SHE serves as a reference point to compare and measure the reduction potentials of other half-cell reactions. The standard reduction potentials of other chemical species are measured in relation to the value of the SHE under standard conditions and are expressed in volts (V).

Key concepts

Chemical Species Reduction

The process of chemical species reduction plays a critical role in electrochemistry and involves the gain of electrons by a substance. When a species undergoes reduction, it experiences a decrease in its oxidation state, indicating that it has become more negatively charged. This phenomenon is the fundamental basis for redox (reduction-oxidation) reactions, which are essential for the generation of electrical energy in batteries and for many other chemical processes.

For instance, when a metal ion in solution accepts electrons, it is reduced to its solid metal form. This can be represented by the simple equation: \[ \text{Metal}^{n+} + ne^- \rightarrow \text{Metal} \]
where \( n \) represents the number of electrons transferred, and \( e^- \) symbolizes an electron. Understanding the tendency of a chemical species to be reduced is crucial when predicting the direction of redox reactions and for the design of various electrochemical devices.

Standard Conditions for Reactions

Standard conditions for reactions, specifically in the context of electrochemistry, refer to the set of predefined parameters under which reactions and their corresponding potential measurements are compared. These conditions are important because they provide a consistent frame of reference for scientists and engineers to evaluate the electrochemical properties of different substances.

The typical standard conditions for electrochemical reactions are:

• Temperature: 298 K (25°C)
• Pressure: 1 atmosphere (atm)
• Concentration: 1.0 M for all solutes in an aqueous solution

When reactions occur under these uniform conditions, they provide reliable data for the standard reduction potential, facilitating comparability across different chemical systems. Any deviation from these conditions can result in variations in potential, which need to be carefully accounted for when interpreting electrochemical measurements.

Standard Hydrogen Electrode (SHE)

The Standard Hydrogen Electrode (SHE) is a critical component in electrochemical studies and is universally employed as a reference point for the measurement of electrode potentials. The SHE is composed of a platinum electrode surrounded by hydrogen gas at 1 atm pressure, and immersed in a 1.0 M aqueous solution of hydrogen ions (H+). Its design ensures that the half-cell reaction for hydrogen gas undergoing reduction at the electrode's surface can be written as:
\[\text{H}_2(g) + 2\text{e}^- \rightarrow 2\text{H}^+(aq)\]

By definition, the SHE has a reduction potential of 0 volts under standard conditions, serving as a true zero point against which all other electrode potentials are gauged. This allows chemists and physicists to compile a table of standard reduction potentials for all elements, using the SHE as the comparative baseline, thus enabling predictive insights into the electrical tendencies of different elements and compounds.

Electrochemical Measurements

Electrochemical measurements are vital for determining the properties of various chemical species with respect to their ability to donate or accept electrons. These measurements often involve the use of voltmeters or potentiometers to ascertain the potential difference between an electrode of interest and a reference electrode, such as the SHE. The potential difference or voltage obtained signifies the propensity of a chemical species to gain or lose electrons under electrochemical conditions.

Understanding the reduction potential of electrodes is particularly important, as it allows scientists to deduce the spontaneity of redox reactions and to construct electrochemical cells, such as galvanic cells or batteries. The ability to accurately measure these potentials under standardized conditions is essential for the advancement of technologies that rely on electrochemical reactions, like fuel cells, corrosion prevention, and even metallurgical processes.