Electrolysis and Electrolytic Cells Quiz

Electrochemistry

• Electrochemistry involves chemical changes in chemical systems, including chemical reactions that produce electricity and the changes associated with current flow through matter.
• Redox reactions (electron transfer) are central to these systems.
• Metals can be purified or electroplated using electrochemical methods.
• Devices like automobiles, smartphones, and many more use batteries for power.
• All electrochemical systems involve electron transfer in a reacting system.
• Reactions often occur in a region called a cell where electron transfer occurs at electrodes.

Electrolytic Cell

• An electrolytic cell is an apparatus used for electrolysis.
• It's a cell/device that produces chemical reactions through direct current flow.
• A system of electrodes and electrolytes are used to drive non-spontaneous redox reactions.
• This is a reaction system where a redox reaction happens with an electric current's help.

Electrolysis

• Electrolysis is a process that uses electrical energy to induce a non-spontaneous chemical reaction.
• It's the decomposition of an ionic system/electrolyte by direct electric current.
• Electrolysis uses electric current to cause redox reactions.

Electrodes

• Electrodes (anode and cathode) are metal strips or carbon plates (graphite) that allow current to enter or leave an electrolyte.
• Electrodes can be active or inert.
• Inert electrodes don't participate in the electrolytic reaction and their sizes stay the same (e.g., platinum, graphite).
• Active electrodes do participate in the processes and their sizes change (e.g., Cu, Zn, Pb, Sn).

Anode

• An anode is a positive electrode.
• Current enters through it, or electrons leave the electrolyte.
• Oxidation (loss of electrons) occurs at the anode.

Cathode

• A cathode is a negative electrode.
• Current leaves through it, or electrons enter the electrolyte.
• Reduction (gain of electrons) occurs at the cathode.

Electrolyte

• An electrolyte is a compound that conducts electricity in molten or aqueous states.
• It decomposes in the electrolytic process.
• Strong electrolytes completely ionize/dissociate in aqueous/molten states, good conductors of electricity. Examples: CuSO4, ZnSO4, HCl, H2SO4, HNO3, NaCl
• Weak electrolytes only slightly/partially ionize, are poor conductors of electricity. Examples: H2O, NH3, CH3COOH, CH3NH2
• Non-electrolytes do not ionize in aqueous/molten states and are non-conductors of electricity. Examples: sugar, benzene, alcohol

lonic Theory of Electrolysis

• When an electrolyte is melted or dissolved in water, species dissociate into freely moving ions.
• Anions move toward the anode (positive).
• Cations move toward the cathode (negative).
• The number of electrical charges carried by an ion equals its valency.

Mechanism of Electrolysis (Aqueous)

• When the electrolyte is aqueous, it's dissociated with water.
• For example, CuSO4 (aq) → SO42−(aq) + Cu2+(aq).
• H2O → H+(aq) + OH−(aq)

Mechanism of Electrolysis (Molten)

• When the electrolyte is molten, the electrolyte dissociates alone.
• For example, CaCl2 → Ca2+(l) + 2Cl−(l)

Electrochemical Series

• The electrochemical series arranges metallic elements/ions based on specified conditions.
• It shows the tendency of one metal to reduce the ions of another below it in the series.
• Cations (to cathode): K+, Na+, Ca2+, Mg2+, Al3+, Zn2+, Fe2+, Sn2+, Pb2+, H+, Cu2+, Hg2+, Ag+, Au+ (increasing preference for discharge/decreasing electropositivity)
• Anions (to anode): F-, SO42-, NO3-, Cl-, Br-, I-, OH- (increasing preference for discharge/decreasing electronegativity)

Factors Influencing Discharge of Ions

• Concentration of ions (higher concentration generally leads to easier discharge). The position of competing ions in the series is also important.
• Nature of electrodes (active vs. inert).
• Position of ions in the electrochemical series (less electropositive ions tend to discharge first).
• Size and duration of current passed (affects the overall amount of ions discharged).

Electrolysis of Dilute NaCl

• NaCl decomposes to Na+ and Cl-.
• Water decomposes to H+ and OH-.
• OH- are preferentially discharged at the anode.
• H+ are discharged in preference to Na+ at the cathode.

Electrolysis of Brine (Concentrated NaCl)

• This process leads to the discharge of Cl⁻ at the anode.
• H+ discharge at the cathode, because H+ and Na+ are farther apart in the series, concentration does not count.

Electroplating

• Electroplating coats an inferior metal with a superior one using electrolysis.
• The object to be plated is the cathode.
• The plating metal is the anode.
• The electrolyte is a salt of the plating metal.

Purification of Metals

• Electrolysis is a useful method for purifying metals.
• Impure metal is the anode.
• Pure metal is the cathode.
• A solution of a soluble salt of the metal serves as the electrolyte.

Faraday's Laws of Electrolysis

• Law 1: The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity passed. (m ∝ Q)
• Law 2: When the same quantity of electricity is passed through different electrolytes, the masses of the substances liberated or deposited are proportional to their equivalent masses. (m ∝ E).

Factors Affecting the Amount of Products Deposited

• Magnitude of the steady current passed
• Duration of the steady current
• Ionic charges of the liberated element

Important Applications of Electrolysis

• Electroplating
• Extraction of metals
• Purification of metals
• Production of chemicals (e.g., H2, O2, Cl2, NaOH)