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EnglandChemistry

C3 Chemical reactions

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

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

Electrolysis of molten and aqueous compounds, the movement of ions to the electrodes, predicting the products at the cathode and anode, half equations at the electrodes, and the extraction of reactive metals.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.4 on electrolysis, covering the electrolysis of molten and aqueous compounds, the movement of ions to the electrodes, predicting the products at each electrode, half equations, and the extraction of reactive metals such as aluminium.
10 min answer →

Why do some reactions give out heat and others take it in, and how do we show this on an energy diagram?

Exothermic and endothermic reactions and their uses, reaction profiles, activation energy, and calculating the overall energy change from bond energies.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.2 on energetics, covering exothermic and endothermic reactions and their uses, reaction profiles and activation energy, and calculating the overall energy change of a reaction from bond energies.
9 min answer →

How do we represent chemical reactions with equations, and why is mass always conserved?

Word and balanced symbol equations, conservation of mass, balancing equations, ionic equations, and explaining apparent mass changes in open systems.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.1 on chemical equations and conservation of mass, covering word and balanced symbol equations, how to balance equations, ionic equations, and explaining apparent changes in mass in open systems.
9 min answer →

What do oxidation and reduction mean, in terms of both oxygen and electrons?

Oxidation and reduction in terms of oxygen and electrons, redox reactions, oxidising and reducing agents, and writing half equations for the loss and gain of electrons.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.3 on oxidation and reduction, covering the definitions in terms of oxygen and electrons, redox reactions, oxidising and reducing agents, and writing half equations for electron loss and gain.
8 min answer →

What is the mole, and how do we use it to calculate reacting masses?

Relative formula mass, the mole and the Avogadro constant, calculating moles from mass, using mole ratios to find reacting masses, limiting reactants, and percentage yield.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.1 on the mole and reacting masses, covering relative formula mass, the mole and the Avogadro constant, calculating moles from mass, using mole ratios for reacting masses, limiting reactants, and percentage yield.
10 min answer →

How do acids react with metals, bases and carbonates, and what does the pH scale tell us?

The reactions of acids with metals, bases and carbonates, neutralisation, salts, the pH scale, strong and weak acids, and making soluble salts.
A focused answer to OCR Gateway GCSE Chemistry A topic C3.3 on acids and bases, covering the reactions of acids with metals, bases and carbonates, neutralisation and salts, the pH scale, the difference between strong and weak acids, and making soluble salts.
9 min answer →