Bases vs Alkalis
Cambridge IGCSE Chemistry 0620 · Core Level
🥊 The Nightclub Analogy
Acids — The Troublemakers 🔴
Proton donors. They cause chaos — they corrode, react, and attack. pH below 7.
Bases — The Bouncers 🟤
Metal oxides or metal hydroxides. Their job is to neutralise acids. But some are too heavy to move — they stand at the door and don't go into the pool (water).
Alkalis — The Swimming Bouncers 🔵
An alkali is a base that dissolves in water. It's a bouncer who can also swim! NaOH jumps in the pool — it's still a base, but now it's also an alkali. CuO? It sinks.
All Alkalis are Bases — but NOT all Bases are Alkalis.
Condition: Solubility in water. If it dissolves → Alkali. If it doesn't → just a Base.
🔬 The Solubility Tank — Drop It In!
Select a substance and watch what happens when it hits water.
🗂️ Venn Diagram Sorter
Drag each substance into the correct zone.
⚫ Bases Only
(insoluble in water)
🔵 Alkalis
(soluble bases)
⚗️ Neutralisation Bench — CuO + H₂SO₄
Watch an insoluble base neutralise an acid. Stage by stage.
Word Equation:
Copper(II) oxide + sulfuric acid → copper(II) sulfate + water
Symbol Equation:
CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
Before
Yellow acid + black powder
After
Clear blue solution
⚠️ EXAMINER TRAP
CuO neutralises the acid — proving it IS a base. But it never dissolved on its own — so it is NOT an alkali. The product CuSO₄ dissolves because it's a salt, not because CuO is soluble!
📖 Definition Match — Reveal When Ready
🎯 Summary — The 3 Laws
Common Alkalis (Cambridge List)
NaOH — sodium hydroxide | KOH — potassium hydroxide | Ca(OH)₂ — calcium hydroxide | NH₃(aq) — ammonia solution
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