Lesson Plan: Tests for Cations Chemistry

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to identify aqueous positive ions based on their reactivity and the color and solubility of their salts.

Objectives

Students will be able to

  • describe the colors and solubilities of precipitates when NaOH is added to various metal cations in aqueous solution (Cu2+, Fe2+, Fe3+, Al3+, Zn2+, Ca2+, and Cr3+),
  • describe the colors and solubilities of precipitates when aqueous ammonia is added to various metal cations (Cu2+, Fe2+, Fe3+, Al3+, Zn2+, Ca2+, and Cr3+) in aqueous solution,
  • identify which precipitates redissolve when excess NaOH or ammonia is added,
  • describe the test for the ammonium cation using NaOH (no precipitate and pungent ammonia gas is produced),
  • identify which metal cations require both the hydroxide and aqueous ammonia test to confirm which metal cation is present,
  • write ionic equations for the reaction between metal cations and the hydroxide anion,
  • identify an unknown metal ion from the results of the above tests.

Prerequisites

Students should already be familiar with

  • ions,
  • metals,
  • precipitates.

Exclusions

Students will not cover

  • flames tests,
  • atomic emission spectroscopy,
  • tests for anions.

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