Topic 4: Chemical Changes (AQA GCSE Chemistry – Combined Science)
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Q: What is the pH scale?
A: A scale from 0 to 14 that shows how acidic or alkaline a solution is
Q: What pH is neutral?
A: pH 7
Q: What is an acid in terms of ions?
A: A substance that releases H⁺ (hydrogen ions) in solution
Q: What is an alkali in terms of ions?
A: A base that dissolves in water to release OH⁻ (hydroxide ions)
Q: What is the general word equation for a neutralisation reaction?
A: Acid + base → salt + water
Q: What type of reaction is neutralisation?
A: Exothermic
Q: What is the ionic equation for neutralisation?
A: H⁺ + OH⁻ → H₂O
Q: What is a base?
A: A substance that reacts with an acid to form a salt and water (includes alkalis, metal oxides, and metal hydroxides)
What is a salt?
A: A compound formed when the hydrogen in an acid is replaced by a metal or ammonium ion
Q: What salt is formed from hydrochloric acid?
A: A chloride
Q: What salt is formed from sulfuric acid?
A: A sulfate
Q: What salt is formed from nitric acid?
A: A nitrate
Q: What is the general equation for acid + metal?
A: Acid + metal → salt + hydrogen
Q: What is the test for hydrogen gas?
A: A lit splint makes a squeaky pop
What is the general equation for acid + metal oxide?
A: Acid + metal oxide → salt + water
What is the general equation for acid + metal hydroxide?
A: Acid + metal hydroxide → salt + water
Q: What is the general equation for acid + metal carbonate?
A: Acid + metal carbonate → salt + water + carbon dioxide
Q: How can you test for carbon dioxide?
A: Bubble gas through limewater — it turns cloudy
Q: What is the reactivity series?
A: A list of metals ordered by their reactivity with water and acids
: Name the metals at the top and bottom of the reactivity series. A:
Top: Potassium, sodium, calcium Bottom: Silver, gold, platinum
What is a displacement reaction?
A: A more reactive metal displaces a less reactive metal from its compound
Q: What is oxidation in terms of electrons?
A: Loss of electrons
Q: What is reduction in terms of electrons?
A: Gain of electrons
Q: What is the acronym for oxidation and reduction?
A: OIL RIG – Oxidation Is Loss, Reduction Is Gain (of electrons)