Chemical Changes

Chemical Changes covers the reactivity series, oxidation and reduction, extraction of metals, reactions of acids, salt preparation, the pH scale, neutralisation, titrations and electrolysis.

The reactivity series is the spine of the unit and worth learning thoroughly, since it explains displacement reactions and how each metal is extracted. Acids and bases follow, with the preparation of a soluble salt being a required practical examined in detail. Electrolysis is the topic students find hardest, because it requires tracking which ion moves to which electrode and what happens there — remember that positive ions move to the negative electrode. Half equations are a frequent source of lost marks, particularly the electrons. Titration questions reward careful arithmetic and an understanding of why concordant results matter.