← Chemistry syllabus

EnglandChemistry

Topic 3: Chemical changes

4 dot points across 4 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What is the pH scale, and what is the difference between strong, weak, dilute and concentrated acids?

Acids, bases and the pH scale: hydrogen and hydroxide ions, indicators, the pH scale and hydrogen ion concentration, strong and weak acids, dilute and concentrated, and neutralisation.
A focused answer to Edexcel GCSE Chemistry topic 3, covering acids as sources of hydrogen ions and alkalis as sources of hydroxide ions, indicators, the pH scale and how it relates to hydrogen ion concentration, the difference between strong and weak acids and between dilute and concentrated, and neutralisation.
9 min answer →

How does electrolysis split compounds, and what is formed at each electrode?

Electrolysis: electrolysis of molten ionic compounds and aqueous solutions, predicting the products at the electrodes, writing half-equations, and the electrolysis of copper sulfate core practical.
A focused answer to Edexcel GCSE Chemistry topic 3, covering what electrolysis is, the electrolysis of molten ionic compounds, the rules for predicting products at the cathode and anode in aqueous solutions, writing half-equations, oxidation and reduction at the electrodes, and the copper sulfate electrolysis core practical.
10 min answer →

How do we prepare a pure, dry sample of a soluble or an insoluble salt?

Preparing salts: making a soluble salt from an insoluble base, the titration method for soluble salts of soluble bases, preparing insoluble salts by precipitation, and the two core practicals.
A focused answer to Edexcel GCSE Chemistry topic 3, covering how to prepare a pure dry soluble salt from an acid and an insoluble base, the acid-alkali titration method for soluble salts, the copper sulfate core practical, preparing insoluble salts by precipitation using solubility rules, and obtaining a pure dry sample.
10 min answer →

What salts and other products form when acids react with metals, oxides, hydroxides and carbonates?

Reactions of acids: the general reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates, the salts produced, and the tests for hydrogen and carbon dioxide.
A focused answer to Edexcel GCSE Chemistry topic 3, covering the general reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates, the salts each acid produces, writing balanced and ionic equations, and the chemical tests for hydrogen and carbon dioxide.
9 min answer →