In this chemistry lesson, the focus is on understanding water hardness, specifically identifying hard water caused by calcium and magnesium ions, and methods to remove temporary hardness. The lesson also reviews reactions between metals and water, highlighting that potassium, sodium, and calcium react vigorously with cold water to produce hydrogen gas and a soluble metal hydroxide, while less reactive metals like magnesium require steam to react. Additionally, the lesson explores chlorine’s reaction with water forming hydrochloric and hypochlorous acids (bleach), and the effects of chlorine on blue litmus paper, as well as the reaction of carbon with steam to produce carbon monoxide and hydrogen.