Electrolysis of Solutions

Lesson Overview

In this activity, students will observe the results of electrolysis of aqueous solutions, then identify the products of the reactions at the cathode and anode. From their observations and also through testing the products qualitatively, students will write equations, first as half reactions and then as net ionic equations, for each electrolysis event.

Student Ability Level and Grouping

This lab is meant for average and advanced students, depending on the extent to which the basics of redox principles have been studied in class. Students should work in groups of 3 to 4.

Expected Student Background and Skills

Prior to carrying out the activity students should

  • be able to skillfully manipulate basic lab equipment;
  • have a basic understanding of the principles behind oxidation and reduction; and
  • be able to write equations that describe the basic activity at each of the electrodes (anode and cathode).

Time and Materials Required

The expected time to complete the activity is two 45-minute periods.

Consumables

  • Solutions of potassium bromide, sodium sulfate, potassium iodide, sodium chloride, copper (II) sulfate, and lead nitrate
  • Starch solution
  • Universal indicator
  • Distilled water
  • Cloth or filter paper strips

Non-consumables

  • Small-scale pipets
  • Electrolysis apparatus (student-made; instructions included in teacher guide)
  • Nine-volt battery (or conductivity apparatus with nine-volt battery)
  • Microplate (12 wells)

Learning Objectives

After completing this activity, students should understand

  • basic laboratory techniques for identifying specific chemical products of electrolysis;
  • the basic chemistry behind the electrolytic change of the reactants to products; and
  • the kind of electrical activity taking place at each electrode (cathode and anode).

In addition, students should be able to

  • mentally “trace” the flow of electrons within the circuit;
  • distinguish between an aqueous solution of an ionic compound and a molten sample of an ionic compound; and
  • write equations that describe the electrolytic activity at each electrode for each reaction that takes place.

National Science Education Standards

Unifying Concepts and Processes

  • Evidence, models, and explanations
  • Change, constancy, and measurement

Science as Inquiry

  • Abilities necessary to do scientific inquiry
  • Understandings about scientific inquiry

Physical Science

  • Chemical reactions

Science in Personal and Social Perspective

  • Science and technology in society

History and Nature of Science

  • Science as human endeavor
  • Nature of science
  • History of science

Download the Activity

Connect with CHF