Alkalis & BasesOxford AQA IGCSE Chemistry: Flashcards

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What is a base?

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What is a base?: A substance that neutralises an acid to form a salt and water; metal oxides and metal hydroxides are bases.
What is an alkali?: A base that dissolves in water, releasing hydroxide ions, OH⁻(aq).
Are all bases alkalis?: No — an alkali must be soluble in water; most bases (e.g. most metal oxides) are insoluble.
What happens when ammonia dissolves in water?: It produces an alkaline solution.
What is ammonia used to produce when reacted with acids?: Ammonium salts, e.g. ammonium nitrate, used as fertilisers.
What is limewater?: A solution of calcium hydroxide in water.
What happens when carbon dioxide is bubbled through limewater?: It turns cloudy/milky as insoluble calcium carbonate forms.
Write the word equation for limewater reacting with CO₂.: Calcium hydroxide + carbon dioxide → calcium carbonate + water.
Name two examples of metal hydroxides that are alkalis.: Sodium hydroxide (NaOH) and potassium hydroxide (KOH).
What ion do alkalis release in solution?: Hydroxide ions, OH⁻(aq).
Give the formula for ammonia.: NH₃.
What test does the limewater reaction provide?: The standard laboratory test for carbon dioxide gas.