Electrolysis: Principles, Processes, and Applications

Comprehensive vocabulary flashcards covering the concepts, definitions, classifications, and commercial applications of electrolysis from lecture notes.

Electrolysis

The process where an electric current is passed through a substance (electrolyte) in its molten or aqueous state, resulting in a chemical reaction that causes it to decompose into its constituent ions.

Electrolyte

A compound which either in aqueous solution or in molten state allows electric current to pass through it, consisting of molten salts or solutions of salts, acids, and alkalis.

Non-electrolyte

A compound which neither in solution nor in the molten state allows an electric current to pass through it, does not decompose at the electrodes, and contains only molecules (e.g., distilled water, alcohol, kerosene, cane sugar, urea).

Degree of dissociation ($\alpha$)

The fraction of electrolyte molecules split into ions, defined by the formula $\alpha = \frac{\text{Number of molecules dissociated}}{\text{Total number of molecules}}$.

Strong electrolyte

An electrolyte that dissociates almost completely into free mobile ions in fused or aqueous solution state, conducts a large amount of electricity, and allows a bulb to glow brightly (e.g., $HCl$, $H_2SO_4$, $NaOH$, $NaCl$).

Weak electrolyte

An electrolyte that partially dissociates in fused or aqueous solution state, contains ions as well as molecules, conducts small amounts of electricity, and allows a bulb to glow dimly (e.g., carbonic acid, acetic acid, $NH_4OH$).

Electrolytic cell (voltameter)

A non-conducting vessel containing two electrodes immersed in a solution of electrolytes used to bring about a chemical reaction, requiring an outside DC source to convert electrical energy into chemical energy.

Electrochemical cell

A device used to convert chemical energy into electrical energy (e.g., simple voltaic cell, Daniel cell).

Electrodes

Two metal plates, wires, graphite rods, or gas carbon rods immersed in the electrolyte through which the electric current enters and leaves the electrolytic cell.

Anode

The positive electrode connected to the positive terminal of the battery where electrons leave the electrolyte, oxidation takes place, and anions migrate.

Cathode

The negative electrode connected to the negative terminal of the battery by which electrons enter the electrolyte, reduction takes place, and cations migrate.

Cation

A positively charged ion that carries a positive charge equal to its valency, migrates to the cathode during electrolysis, and gains electrons to become a neutral atom.

Anion

A negatively charged ion that carries a negative charge equal to its valency, migrates to the anode during electrolysis, and loses electrons to become a neutral atom.

Oxidation (electronic concept)

The process in which an atom or an ion loses electron(s); also chemically defined as the addition of oxygen or the removal of hydrogen.

Reduction (electronic concept)

The process in which an atom or an ion gains electron(s); also chemically defined as the removal of oxygen or the addition of hydrogen.

Oxidising agent

A substance that oxidises other substances by either accepting electrons or providing oxygen or an electronegative ion (or by removing hydrogen or an electropositive ion).

Reducing agent

A substance that reduces other substances by providing electrons, providing hydrogen or an electropositive ion, or removing oxygen or an electronegative ion.

Electrolysis of molten lead bromide

The decomposition of molten $PbBr_2$ conducted above $380^\circ\text{C}$ in a silica crucible with inert graphite electrodes, yielding silvery gray lead at the cathode ($Pb^{2+} + 2e^- \rightarrow Pb$) and reddish brown bromine fumes at the anode ($2Br^- - 2e^- \rightarrow Br_2$).

Electrolysis of acidified water

The decomposition of water containing traces of non-volatile dilute $H_2SO_4$ using inert platinum electrodes, yielding hydrogen at the cathode and oxygen at the anode in a $2:1$ ratio by volume.

Active electrode

An electrode (such as copper in aqueous copper sulphate) that takes part in the electrolytic reaction by losing electrons and dissolving as ions into the solution rather than allowing electrolyte anions to discharge.

Electroplating

A process in which a thin film of a metal like gold, silver, nickel, or chromium is deposited on another metallic article using direct current for decoration or protection against corrosion.

Sodium argentocyanide ($Na[Ag(CN)_2]$)

A complex salt electrolyte used for silver electroplating to ensure smooth, slow, and uniform deposition of silver rather than rapid, non-uniform plating.

Electrolytic refining of metals

A commercial process in which impure slabs of a metal serve as the anode and thin pure strips serve as the cathode to purify metals (such as copper) to high electrical conductivity.

Anode mud

The insoluble impurities that settle down at the bottom of the cell below the anode during the electrolytic refining of impure metal slabs.