Question 1
Complete and balance: Al³⁺ + __ → __.
Need a hint for Question 1?
Balance atoms first, then compare total charge and add electrons.
Check Question 1
Al³⁺ + 3e⁻ → Al.
STUDENT SPACE · TOPIC 2
Electrode half-equations
Construct balanced oxidation and reduction half-equations.
The essentials
- A metal ion gains electrons and becomes a neutral atom.
- Bromide ions lose electrons. Two bromine atoms form one Br₂ molecule.
- Pb²⁺ + 2e⁻ → Pb has total charge 0 on both sides.
Key vocabulary
| English | Chinese |
|---|---|
| cation | 阳离子 |
| anion | 阴离子 |
| discharge | 放电 |
| charge balance | 电荷守恒 |
Quick practice
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Question 2
Write the cathode half-equation for molten MgCl₂.
Need a hint for Question 2?
Positive magnesium ions gain electrons.
Check Question 2
Mg²⁺ + 2e⁻ → Mg.
Question 3
Write the anode half-equation for molten MgCl₂ and explain whether it is oxidation or reduction.
Need a hint for Question 3?
Balance chlorine atoms and charge; identify electron loss or gain.
Check Question 3
2Cl⁻ → Cl₂ + 2e⁻. Oxidation because chloride ions lose electrons.
Use Lesson 2 in your worksheet for written practice. Your teacher will discuss those answers in class.
Electrolytic cell · a power supply drives change
Electrons carry charge in metal wires. Ions carry charge in the electrolyte.
Predict first: Name both products and write the half-equations. What changes if you change the anode material?
Schematic teaching model: motion and particle numbers are illustrative. Moving anions do not necessarily discharge: electrode material and competing ions determine products.
PREDICT · TRY · EXPLAIN · 3–5 MINUTES
Inside an electrolytic cell
Predict the product at each electrode. Run the cell, then explain where ions and electrons move.
Molten PbBr₂; inert electrodes. This is a model, not a home experiment.
DC power supply
− supplies electrons to cathode · + removes electrons from anode
− supplies electrons to cathode · + removes electrons from anode
− Cathode
Reduction+ Anode
Oxidation
Reduction+ Anode
Oxidation
← Pb²⁺ cationsBr⁻ anions →
Electrons travel through wires and electrodes. Ions carry charge through the electrolyte. Movement towards an electrode does not mean an ion must be discharged there.