Electrolysis Essentials
Shared 11/27/2025•117 views
1. Electrolytes & Non-Electrolytes Strong Electrolyte: Strong acid + Strong base $\rightarrow$ NaCl + H$_2$O Weak Electrolyte: Weak base + Weak electrolyte $\rightarrow$ NH$_4$OH + H$_2$CO$_3 \rightarrow$ (NH$_4$)$_2$CO$_3$ + H$_2$O 2. Electrolysis of PbBr$_2$ Solid PbBr$_2$: Particles present are Pb$^{2+}$, Br$^-$ (ionic lattice, no free movement) Molten PbBr$_2$: Particles present are Pb$^{2+}$, Br$^-$ (ions are free to move, conduct electricity) 3. Electrolysis Concepts Mass of Cathode Increases Mass of cathode increases because reduction of Cu$^{2+}$ is taking place at the cathode, forming metal. Cu Anode Dissolves A Cu anode gets oxidized because it is reactive/attackable. OH$^{-}$/Cu$^{2+}$ discharged preferentially because they lie lower in the electrochemical series. 4. Electrolysis of Acidified Water / CuSO$_4$ Reaction: $2\text{OH}^- + 2\text{OH}^- \rightarrow 2\text{H}_2\text{O} + \text{O}_2\uparrow$ At Cathode: Concentration of H$_2$SO$_4$ decreases. At Anode: Concentration of H$_2$SO$_4$ increases. Overall: Mass of H$_2$SO$_4$ remains same. 5. Electrolysis of CuSO$_4$ (using inert electrodes) Cu ions deposition completed. Then, electrolysis of water takes place. After initial products, H$_2$ is produced. At cathode, H$_2$ produced. At anode, O$_2$ produced. The blue color of solution fades away as Cu$^{2+}$ ion concentration in the electrolytic solution decreases. Solution becomes totally colorless as Cu$^{2+}$ ions are totally finished. 6. Electrolysis of CuSO$_4$ (using Cu electrodes) The blue color of solution does not fade away. For every Cu$^{2+}$ ion discharged at cathode to a neutral Cu atom to be deposited as Cu metal, a new (another) Cu$^{2+}$ ion is released/passed into the electrolyte solution by the Cu anode (reactive). Mass of cathode increases; mass of anode decreases. 7. Electroplating Ag/Ni Why AgNO$_3$ is not directly used: AgNO$_3 \rightleftharpoons \text{Ag}^+ + \text{NO}_3^-$ The release of Ag$^+$ ions into the electrolytic solution in this case is at a very high/fast rate, which leads to uneven/non-uniform/not smooth deposition/coating of the metal on the article to be electroplated. Why K[Ag(CN)$_2$] solution is used: K[Ag(CN)$_2$] $\rightleftharpoons \text{K}^+ + \text{Ag}^+ + 2\text{CN}^-$ Being a complex salt, the release of Ag$^+$ ions into the electrolytic solution in this case is at a slower rate, leading to even, uniform, smooth deposition/coating of Ag metal on the article. Observations: Anode: The mass of anode decreases because the Ag anode itself gets oxidized (it is a reactive/attackable electrode). Cathode: Mass of cathode increases, Ag metal is deposited. Ag$^+$ gets reduced to silver Ag metal.