Unit 3 Chemistry: Electrolysis Flashcards

This set of vocabulary flashcards covers the fundamental concepts, commercial processes, and quantitative laws of electrolysis as presented in the Unit 3 Chemistry lecture.

Electrolysis

The use of electricity to drive non-spontaneous redox reactions by passing a direct current ($DC$) through a conducting liquid.

Electrolytic cell

A cell that transforms electrical energy into chemical energy through endothermic reactions.

Cathode (Electrolytic)

The negative electrode that receives electrons from the power source and where reduction occurs.

Anode (Electrolytic)

The positive electrode that loses electrons to the power source and where oxidation occurs.

Molten ionic compound electrolysis

The process where salts are melted at high temperatures to allow ions to move to electrodes; for example, the electrolysis of molten $NaCl$ to produced $Na(l)$ and $Cl_2(g)$.

Competition at the electrodes

The occurrence where multiple species can react at an electrode; the strongest oxidant reacts at the cathode and the strongest reductant at the anode based on the electrochemical series.

Spectator ions

Ions that remain in solution and do not participate in the redox reactions during electrolysis.

Downs cell

A commercial electrolytic cell used to produce sodium metal and chlorine gas from molten $NaCl$, utilizing a mesh screen to separate products.

Membrane cell

A commercial electrolytic cell that produces $NaOH$, $Cl_2$, and $H_2$ from concentrated $NaCl$ solution (brine) using a semipermeable membrane.

Brine

A concentrated solution of sodium chloride ($NaCl$) used in the membrane cell.

Hall-Héroult cell

A commercial electrolytic cell used to obtain pure aluminium from alumina ($Al_2O_3$).

Alumina

Aluminium oxide ($Al_2O_3$), an extract from the mineral bauxite used in the production of aluminium.

Cryolite ($Na_3AlF_6$)

A chemical additive in the Hall-Héroult cell that allows alumina to stay liquid at $1000^{\text{o}}C$ instead of its normal melting temperature of $2050^{\text{o}}C$.

Electroplating

A commercial electrolysis process used to apply a very thin layer of metal, such as tin or silver, over an object.

Electric charge ($Q$)

The amount of charge in a circuit, measured in coulombs ($C$), calculated as $Q = I \times t$.

Coulomb

The unit of electric charge; one coulomb represents approximately $6.24 \times 10^{18}$ electrons.

Faraday’s first law

A law stating that the mass of product produced at the cathode is directly proportional to the charge passed through the cell ($m \times Q$).

Faraday’s constant ($F$)

The magnitude of electric charge on one mole of electrons, which is exactly $96,500$ coulombs per mole ($96,500 \text{ C mol}^{-1}$).

Faraday’s second law

A law stating that the production of one mole of a substance in an electrolytic cell requires the passage of a whole number of moles of electrons (1, 2, 3, etc.).

Energy ($E$)

In electrolysis calculations, energy is related to charge by the equation $E = V \times Q$, where $V$ is voltage and $Q$ is charge.