Which of the following aqueous solution produces metal after electrolysis ? (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{KMnO}_{4}\) (c) \(\mathrm{CH}_{3} \mathrm{COONa}\) (d) \(\mathrm{CuCl}_{2}\).

In the realm of chemistry education, understanding the reduction of metal cations during electrolysis is fundamental. This process occurs at the cathode, which is the negatively charged electrode in an electrolysis cell. During electrolysis, cations, which are positively charged ions, migrate towards the cathode. Here, they gain electrons and are converted from their ionic form into their elemental metallic form.

It's crucial to note that not all metal cations can be reduced to form metals when an electric current is passed through an aqueous solution. The feasibility of this reduction depends on the electrode potential of the metal, which can be referenced from the electrochemical series. Metals like copper can easily be reduced due to their lower electrode potentials, while others with higher potentials compared to hydrogen, such as potassium and sodium, won't be reduced in aqueous solutions under standard conditions.

One of the most critical concepts in electrochemistry is the electrode potential, also known as reduction potential. This is a measure of the tendency of a chemical species to be reduced (gain electrons) and is measured in volts. Each metal has a characteristic electrode potential, which determines how easily it can be reduced during electrolysis.

Electrode potentials are invaluable for predicting the outcome of electrolysis. For instance, if you compare the electrode potentials of copper and hydrogen, you'll find that copper has a more favorable (lower) electrode potential. This implies that in an aqueous solution, where the competition is between the reduction of metal cations and hydrogen ions (from water), copper ions will be reduced preferentially to form copper metal, provided sufficient voltage is applied.

The decomposition of ionic substances is a primary application of electrolysis. An ionic substance is made up of positive and negative ions held together by strong electrostatic forces in a lattice structure. When dissolved in water, or as a molten liquid, these ions become free to move, allowing them to conduct electricity.

During electrolysis, when an electric current passes through such a solution or molten ionic compound, it causes the ions to move to the electrodes, where they undergo oxidation or reduction reactions. This results in the decomposition of the original compound. For example, electrolyzing copper chloride solution yields copper metal at the cathode by reducing Cu²⁺ ions, and chlorine gas at the anode by oxidizing Cl⁻ ions.