Electrolysis

Summary and Exam Tips for Electrolysis

Electrolysis is a subtopic of Electrochemistry, which falls under the subject Science in the IB MYP curriculum. It involves the breakdown of ionic compounds, either molten or in aqueous solution, through the passage of electricity. Key components include inert electrodes (e.g., platinum), electrolytes, anodes, and cathodes. During electrolysis, cations move to the cathode, gaining electrons, while anions move to the anode, losing electrons, resulting in the formation of atoms.

For example, in the electrolysis of molten lead (II) bromide, $\text{Pb}^{2+}$ ions move to the cathode to form Pb(s), and $\text{Br}^-$ ions move to the anode to form $\text{Br}_2(l)$. In concentrated sodium chloride solution, $\text{H}^+$ ions produce $\text{H}_2(g)$ at the cathode, while $\text{Cl}^-$ ions produce $\text{Cl}_2(g)$ at the anode. The general principle is that metals or hydrogen form at the cathode, while non-metals form at the anode. Electroplating involves coating objects with metal using electrolysis, where the object is the cathode and the coating metal is the anode. Understanding these processes is crucial for predicting the products of electrolysis and constructing ionic half-equations.

Exam Tips

• PANIC: Remember the acronym for electrodes—Positive is Anode, Negative is Cathode.
• Use OIL RIG to recall oxidation and reduction: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
• Inert electrodes like graphite or platinum are essential to prevent side reactions during electrolysis.
• For predicting electrolysis products, identify the ions in the compound, then determine which ions will move to the cathode and anode.
• Practice constructing ionic half-equations to solidify your understanding of the reactions at each electrode.