In electrochemistry, electrolytic cells and electrolysis are key subjects. They are essential for sectors like chemical manufacture, electroplating and metal refining.
Electrolysis is the process of decomposition of an electrolyte by passing electricity through its aqueous solution or molten state.
What is an Electrolytic Cell?
One kind of electrochemical cell that employs electrical energy to drive a chemical process that does not happen on its own is called an electrolytic cell. An electrolytic cell uses electrical energy to cause a chemical change, as opposed to a galvanic (voltaic) cell, which produces electrical energy via a spontaneous reaction.
Faraday’s first law of electrolysis: The amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte (solution or melt).
W α Q or W = QZ =Z x I x t where, Z is electrochemical equivalent of the substance deposited Z = Eq. of substance / 96500
Faraday’s second law of electrolysis: The amount of different substances liberated by the quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalent weights.
W1 / W2 = E1 /E2 where E is the equivalent weight = Atomic mass of element / No. of electrons gained or lost by one atom of the element.
Components of an Electrolytic Cell:
Electrolyte: A material that permits ions to freely flow and conduct electricity, normally a mixture of salts, acids, or bases.
Electrodes: Two conductive substances that to help the electric current flow are known as the cathode (negative electrode) and anode (positive electrode).
External Power Source: A DC (direct current) power supply or battery that supplies the energy required for the reaction. A DC supply is required for charging a battery because a battery stores electrical energy in one direction, and DC current flows consistently in a single direction, allowing for effective charging, while AC current (alternating current) would constantly change direction, negating the charging process by discharging the battery during the opposite current cycle.
What is Electrolysis?
The process by which an electrolytic cell uses electricity to break down a chemical into its component elements is known as electrolysis. Substances are deposited or released at the electrodes as a result of the movement of ions in an electrolyte.
Mechanism of Electrolysis
Ions go toward the oppositely charged electrodes when an electric current flows through an electrolyte during electrolysis:
Cations (positive ions) move in the direction of the cathode, where a reduction reaction takes place and they acquire electrons.
Anions, or negative ions, travel in the direction of the anode, where an oxidation reaction takes place and they lose electrons.
Type of electrolyte and electrodes employed determine the overall chemical reaction.
Examples of Electrolysis
Electrolysis of Water (H₂O)
Water can be decomposed into hydrogen and oxygen gases using electricity.
At the cathode: 2H2O + 2e– — H2 + 2OH– (Reduction)
At the anode: 2H2O — O2 + 4H++ 4e–(Oxidation)
Overall reaction: 2H2O — 2H2 + O2
Electrolysis of Molten Sodium Chloride (NaCl)
The molten state is the liquid form of a substance that was previously solid. It is achieved by heating a solid substance to a very high temperature.
Used in the extraction of sodium and chlorine gas.
At the cathode: Na+ + e– — Na (Reduction)
At the anode: 2Cl– — Cl2 + 2e– (Oxidation)
Electroplating
A method of applying a thin coating of metal on an objects to improve its look or prevent corrosion.
A steel spoon, e.g; serves as the cathode in silver plating, where silver ions from a silver salt solution stay to the spoon.
Factors Affecting Electrolysis
Electrolyte nature: The kind of reaction that takes place is influenced by the ions that are produced by various electrolytes.
Electrode Type: Reactive electrodes, like copper and zinc may dissolve, whereas inert electrodes, like platinum and graphite do not take part in the process.
Ion Concentration: The pace of electrolysis is accelerated on higher ion concentration.
Voltage Applied: Ion mobility and reaction speed are accelerated by higher voltage.
Applications of Electrolysis
There are several practical uses for electrolysis:
Metal Extraction: Electrolysis is used to recover metals such as sodium (from NaCl) and aluminum (from bauxite ore). Ore is a natural rock or sediment that contains valuable minerals in high enough concentrations to be economically mined.
Electroplating: Used to create jewelry, auto parts, and ornaments. (Both terms refer to decorative items, “jewelry” specifically refers to items worn on the body for personal beautification like necklaces, rings and earrings, usually made from precious metals and gemstones, whereas “ornaments” can refer to decorative items used to decorate any object not necessarily meant to be worn on the body, and can be made from a wider range of materials including non-precious metals, glass or even natural elements like shells).
Metal Purification: Electrolysis is a method for purifying impure copper.
Chemical Manufacturing: Brine (saltwater solution is a highly concentrated salt water solution, also known as saltwater. It’s made up of salt and water, and is normally sodium chloride (common salt) or calcium chloride) is electrolysed to give up sodium hydroxide, hydrogen, and chlorine.
Products of Electrolysis:
Electrolyte | Products | Reactions involved | ||
At cathode | At anode | At cathode | At anode | |
Molten NaCl | Na metal | Cl2 gas | Na+(l) + e– — Na(l) | Cl–(l) — ½ Cl2(g) + e– |
Aqueous NaCl | H2 gas | Cl2 gas | H2(l) + e–—½ H2(g) + OH–(aq) | Cl–(aq) — ½ Cl2(g) + e– |
Dil. H2SO4 | H2 gas | O2 gas | H2(aq) + e– —½ H2(g) | 2H2O(l) — O2 (g) + 4H+(aq) + 4 e– |
Conc. H2SO4 | H2 gas | S2O2-8 | H+(aq) + e–— –½ H2(g) | 2SO2-4 (aq) — S2O2-8 (aq) + 2e– |
Summary:
There are several industrial uses for electrolysis and electrolytic cells. Compounds can break down, metals can be extracted, and materials can be deposited by forcing non-spontaneous chemical processes to happen with the use of an external electrical source. Developments in environmental technology, material science and energy storage all depend on an of these ideas.
Note:-
Overvoltage:- Oxidation of H2O is relatively slow process and then, needs extra voltage. This extra voltage needs to oxidize H2O is called overvoltage. Due to overvoltage, the oxidation of chloride ion occurs at anode in preference to H2O.
Discharge voltage:- The minimum voltage that must be applied across the electrodes to bring about the electrolysis and then, discharge of the ions on the electrode is known as discharge voltage. It is infact the ability of ions to discharge first at electrodes.
An electrolytic cell uses electricity to power a non-spontaneous reaction, whereas a galvanic cell produces electricity from a spontaneous reaction.
The chemical reaction in an electrolytic cell requires external energy to occur because it is not spontaneous.
The anode draws anions and experiences oxidation, the cathode attracts cations and experiences reduction.