GCSE Chemistry: Chemical Changes — Topic Revision Workbook

Inside GCSE Chemistry: Chemical Changes — Topic Revision Workbook

put metals in reactivity order and use oxidation and reduction, predict the products of metal + acid and metal + water reactions, extract metals by reduction with carbon, place substances on the pH scale, complete neutralisation word equations and name the salts made, and work out what forms at each electrode in electrolysis. About 30 minutes.

Learning objectives

• metal oxidation and the reactivity series — oxidation as the gain of oxygen and reduction as the loss of oxygen, the order from potassium to gold, and displacement of a less reactive metal by a more reactive one;
• reactions of metals — metal + acid → salt + hydrogen, reactive metal + water → metal hydroxide + hydrogen, and extraction of metals from their oxides by reduction with carbon (or by electrolysis for the more reactive metals);
• acids, alkalis and the pH scale — pH 0–14 with 7 neutral, H+ and OH− ions, neutralisation to a salt and water (plus carbon dioxide with a carbonate), and naming chloride, sulfate and nitrate salts;
• electrolysis — molten and aqueous compounds, ions moving to the anode (positive) and cathode (negative), and the electrolysis of aluminium oxide dissolved in molten cryolite.

Activities in this book

1. Task 1 — Reactivity Series & Metal Oxidation

   oxidation is the gain of oxygen and reduction is the loss of oxygen. The reactivity series lists metals from most reactive (potassium) to least reactive (gold). A more reactive metal will displace a less reactive metal from its compound.

2. Task 2 — Metals with Acids & Water, and Extraction

   metal + acid makes a salt + hydrogen; a reactive metal + water makes a metal hydroxide + hydrogen. Metals less reactive than carbon can be extracted from their oxides by reduction with carbon, but metals more reactive than carbon (like aluminium) must be extracted by electrolysis.

3. Task 3 — Acids, Alkalis, pH & Making Salts

   the pH scale runs from 0 to 14: below 7 is acidic, 7 is neutral, above 7 is alkaline. Acids release H+ ions; alkalis release OH- (hydroxide) ions. Neutralisation makes a salt and water (plus carbon dioxide with a carbonate). Hydrochloric acid makes chlorides, sulfuric acid makes sulfates and nitric acid makes nitrates.

4. Task 4 — Electrolysis

   electrolysis uses electricity to break down an ionic compound that is molten or dissolved in water. Positive ions move to the cathode (negative electrode) and negative ions move to the anode (positive electrode). Aluminium oxide is dissolved in molten cryolite to lower its melting point before electrolysis.

5. Task 5 — Explain a Chemical Change

   this is your 6-mark extended-answer practice. Choose one reaction from Chemical Changes and explain it in full sentences, using the correct keywords and a balanced or word equation. Examiners reward a clear structure, correct science and precise vocabulary.

Suggestions for teaching

• Fix oxidation and reduction first. Define both in terms of oxygen, then apply them to burning magnesium and to reducing iron oxide with carbon before extending to electrons (OIL RIG) for higher tier.
• Anchor everything to the reactivity series. Use the same ordered list to explain displacement, reactions with acid and water, and the choice between carbon reduction and electrolysis.
• Drill the general equations. Rehearse metal + acid → salt + hydrogen, acid + alkali → salt + water and acid + carbonate → salt + water + carbon dioxide until they are automatic.
• Name salts by the acid. Hydrochloric → chlorides, sulfuric → sulfates, nitric → nitrates — then practise full names such as sodium chloride and copper sulfate.
• Make electrolysis physical. Link positive ions to the cathode and negative ions to the anode, and use aluminium oxide in cryolite as the worked example, including why the anodes burn away.