The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:
Electrolyte is the chemical compound that conducts electricity in its molten or aqueous state and undergoes chemical decomposition due to the flow of electricity. It decomposes into ions and neutral atoms at the two electrodes. Electrolytes are ionic or covalent compounds.
They do not conduct electric current at all, whether in a solid or aqueous state. So, they do not undergo decomposition into ions in solution. They contain only molecules.
Distilled water, alcohol, kerosene, cane sugar, carbon disulphide, benzene, glucose, and urea.
Electrolysis is the decomposition of chemical compounds in aqueous solutions or molten states accompanied by chemical change using a direct electric current.
When NaCl is electrolysed, it decomposes into sodium and chlorine gas.
Nacl ⇄ Na⁺ + Cl⁻
At cathode: Na⁺ + e⁻→ Na (Reduction)
At Anode: Cl⁻ – e⁻ →Cl
Cl+ Cl →Cl₂
Reaction: 2NaCl → Na + Cl₂
Metal plates or graphite rods are connected to the terminals of a battery and are immersed into the electrolyte, through which electricity enters and leaves the electrolytic cell.
The electrode connected to the positive pole of the battery is the anode. Anions migrate to the anode, and they are oxidised.
The electrode connected to the negative pole of the battery is the cathode. Cations migrate to the cathode and get reduced.
The atoms or group of atoms that carry a positive or a negative charge are known as ions. Atoms which have positive charge are cations, and negative charge is anions.
Cations: Na⁺, Ca²⁺, Al³⁺
Anions: Po₄³⁻, Cl⁻, OH⁻
The arrangement of ions depends on their ease of being neutralised or discharged during an electrolytic process. The ions are arranged in the order such that the ion at the top is removed with difficulty, and the one at the lower of the series is released quickly.
Selective discharge of ions at electrodes
When two or more ions of the same charge present in an electrolyte solution under similar conditions and are competing for discharge at the same electrode, one gets preferentially discharged. It is known as the selective discharge of ions, and it depends on three factors:
Electrolysis of molten lead bromide
ElectrolyteMolten lead bromide(PbBr₂)Electrolytic cellCrucible made up of silica.ElectrodesCathode: Iron or GraphiteAnode: Graphite plates.
TemperatureAbove 380°C.Electrode reactionsAt cathode: Pb²⁺+ 2e⁻→ PbAt Anode: Br⁻ – e⁻ →Br
Br+ Br→ Br₂
Overall Reaction: PbBr₂→ Pb+ Br₂
Observation Greyish lead deposit at Cathode.Dark reddish-brown vapours at Anode.
Condition ReasonThe article to be electroplated is placed at the cathode.The metal deposits at the cathode by a gain of electrons.The metal to be plated on the article is always made anode and should be replaced frequently.The metal anode dissolves continuously as ions in solution and diminishes in size.Low current should be used for an extended period.Because high current causes uneven deposition of the metal, so low current initiates thicker uniform deposition.A direct current is used instead of A.C current.A.C current causes discharge and ionisation; thereby, no effective coating is provided.The electrolyte must contain the ions of the metal to be plated on the article.Electrolyte dissociates to give metal ions which migrate towards cathode and deposits as neutral metallic atoms.
Electroplating with Nickel
You know that iron gets easily rusted when exposed to the air. To prevent rusting and corrosion, we use electroplating techniques. So, here iron particles are coated with nickel, tin, or zinc to prevent rusting.
Electrolyte: Aqueous solution of Nickel sulphate (NiSO₄)
Cathode: Iron Article
Reaction at cathode: Ni²⁺ + 2e⁻ →Ni (deposited)
Anode: Block of Nickel-metal
The reaction at the anode: Ni – 2e⁻ →Ni²⁺
Refining of a copper
The copper wire used for electric transmission has to be pure because even small impurities reduce its conductivity. When current passes through the electrolyte, copper ions attract the cathode and get deposited on sterile copper strips. The impure copper loses electrons and gives into a solution, and gets finished. The pure copper deposited at the cathode becomes thicker, and it is 99.9% pure.
Electrolyte: Solution of copper sulphate along with dil. Sulphuric acid.
Cathode: Thin strip of pure copper
Reaction at cathode: Cu²⁺ + 2e⁻ →Cu
Anode: Impure copper
The reaction at the anode: Cu – 2e⁻ →Cu²⁺
Electrolytes are substances that dissociate into ions and conduct electricity. Non-electrolytes do not produce ions and do not allow current flow through them. Electrolysis is the process to separate a substance when an electric current passes through an electrolyte. Electrolysis is performed to prevent rusting, extract and purify metals.