A hydrogen electrode and a normal calomel electrode give an...

A hydrogen electrode and a normal calomel electrode give an electromotive force of $0.435 \mathrm{V}$ when placed in a certain solution at $25^{\circ} \mathrm{C}$. $(a)$ What is the $\mathrm{pH}$ of the solution? (b) What is the value of $a_{\mathrm{H}^{+}} ?$

Key Concepts

Hydrogen Electrode

A hydrogen electrode is an electrochemical half-cell based on the oxidation or reduction of hydrogen gas. It is often considered a standard for potential measurements and its electrode potential is directly related to the activity or concentration of hydrogen ions in solution. This makes it a crucial reference in constructing concentration or pH cells and understanding redox reactions in aqueous systems.

Standard Calomel Electrode

The standard calomel electrode is a common reference electrode in electrochemistry that uses mercury(I) chloride (calomel) in contact with a saturated solution of potassium chloride. It has a well-defined and stable electrode potential under standard conditions, making it essential as a reference for measuring electrode potentials in various electrochemical cells.

Nernst Equation

The Nernst equation provides a quantitative relationship between the electrode potential of a half-cell and the activities (or concentrations) of the chemical species involved in the redox reaction. It is a fundamental tool in electrochemistry used to calculate cell potential under non-standard conditions, allowing for the prediction of how changes in concentration, temperature, or pressure affect the potential.

pH is a logarithmic scale used to specify the acidity or alkalinity of an aqueous solution, representing the negative logarithm of the hydrogen ion activity. It is a central concept in chemistry and biochemistry as it affects reaction rates, solubility, and the stability of molecules, thereby influencing a wide range of chemical and biological processes.

Ionic Activity

Ionic activity refers to an effective concentration that accounts for non-ideal behavior in solutions due to interactions between ions. It is more accurate than mere molar concentration in describing the behavior of ions in solution, particularly at higher concentrations, and is critical when applying the Nernst equation as the electrode potential depends on the activity rather than the concentration of the ions.

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