Electrolysis — Part 1: Electrolytes, ions and molten lead bromide: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

Electricity that splits compounds

Part 1 — some substances let an electric current pass and are decomposed by it. This process, electrolysis, is used to extract metals, purify copper and coat objects with a thin layer of metal.

In this lesson you will

Classify substances as strong electrolytes, weak electrolytes or non-electrolytes
Define the terms of electrolysis and link the anode to oxidation and the cathode to reduction
Predict which ions are discharged using the activity series and ion concentration
Describe the electrolysis of molten lead bromide with electrode equations and observations

Table of four substances showing whether each conducts electricity and whether it is decomposed
Substance	Conducts?	Chemical change?
Copper wire	Yes	No
Molten lead bromide	Yes	Yes: lead and bromine form
Ethanoic acid solution	Weakly	Yes, slowly
Sugar solution	No	No

Concept

Electrolytes and non-electrolytes

Electrolyte: a compound that, in the molten state or in aqueous solution, conducts electricity and is decomposed by it.
Strong electrolyte: almost completely ionised; conducts well (sodium chloride, potassium hydroxide, dilute hydrochloric, sulphuric and nitric acids, copper(II) sulphate).
Weak electrolyte: only partly ionised; conducts poorly (ethanoic acid, carbonic acid, ammonium hydroxide solution).
Non-electrolyte: does not conduct in the molten state or in solution (sugar, alcohol, kerosene, carbon tetrachloride).

Table classifying strong electrolytes, weak electrolytes and non-electrolytes with examples
Type	Ionisation	Examples
Strong electrolyte	Almost complete	NaCl, KOH, dilute H₂SO₄, CuSO₄
Weak electrolyte	Partial	CH₃COOH, H₂CO₃, NH₄OH
Non-electrolyte	None	Sugar, alcohol, kerosene

Check your understanding

Quick check: strong or weak?

Classify a set of substances.

Question: Multiple choice

Multiple choice1 mark

Which list contains only strong electrolytes?

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