⚡ Electrochemistry

1. Introduction

Electrochemistry deals with the relationship between electricity and chemical reactions. A major process studied is electrolysis.

Learning Objectives

• Define electrolysis and electrolyte.
• Identify anode and cathode.
• Explain movement of ions.
• Predict products of simple electrolysis.
• Write simple electrode equations.
• Describe electroplating and its uses.

2. Electrolytes

An electrolyte is a substance that conducts electricity when molten or dissolved in water because it contains mobile ions.

Examples include molten sodium chloride and aqueous copper(II) sulfate.

A non-electrolyte does not produce enough mobile ions to conduct electricity, for example sugar solution.

3. Electrolysis

Electrolysis is the chemical decomposition of an ionic compound when electricity is passed through its molten state or aqueous solution.

Remember: RED CAT — Reduction occurs at the Cathode.

4. Electrolysis of Molten Sodium Chloride

Molten NaCl contains Na⁺ and Cl⁻ ions.

At the cathode:

Na⁺ + e⁻ → Na

At the anode:

2Cl⁻ → Cl₂ + 2e⁻

Overall:

2NaCl → 2Na + Cl₂

Sodium forms at the cathode and chlorine gas forms at the anode.

5. Electrolysis of Aqueous Copper(II) Sulfate

With inert electrodes, copper ions are discharged at the cathode and oxygen is commonly produced at the anode.

Copper is deposited at the cathode.

6. Electroplating

Electroplating is the coating of an object with a thin layer of another metal using electrolysis.

Uses

• Improves appearance.
• Protects metals from corrosion.
• Improves surface properties.
• Allows cheaper metals to have a coating of a more attractive metal.

7. Oxidation and Reduction

Oxidation is loss of electrons.

Reduction is gain of electrons.

A useful memory aid is:

OIL RIG — Oxidation Is Loss, Reduction Is Gain.

8. MANEB Examination Focus

• Define electrolysis.
• Identify the cathode and anode.
• Explain movement of ions.
• Predict products at electrodes.
• Write half-equations.
• Explain electroplating.
• Distinguish oxidation from reduction.

9. Practice Exercises

1. Define an electrolyte.
2. Which electrode is negative during electrolysis?
3. Where does reduction occur?
4. Write the half-equation for Cu²⁺ at the cathode.
5. What gas is produced at the anode during molten NaCl electrolysis?
6. State two uses of electroplating.
7. What does OIL RIG mean?

Answers

10. Common Mistakes

• Do not say the cathode is positive during electrolysis.
• Remember that cations move toward the cathode.
• Do not confuse electrolysis with simple electrical conduction.
• Always balance electrons in half-equations.

11. Exam Tip

When answering electrolysis questions, identify the ions first, then decide which ions are discharged at each electrode.