Flashcards · 9202 · Topic 5

Acids, bases and salts flashcards

14 cards on Topic 5, subtopics 3.5.1 to 3.5.2. Pick a subtopic or study them all.

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Base and alkali: Base: a metal oxide or metal hydroxide. Alkali: a soluble hydroxide (a base that dissolves in water). Copper(II) oxide is a base, not an alkali.
Salt: The compound formed when the hydrogen of an acid is replaced by a metal (or ammonium) ion.
Salt endings from hydrochloric, nitric and sulfuric acid: Hydrochloric → chloride. Nitric → nitrate. Sulfuric → sulfate.
acid + metal → acid + metal oxide or hydroxide → acid + ammonia →: salt + hydrogen salt + water an ammonium salt (no water)
Why is a solution of ammonia alkaline?: Ammonia reacts with water to form hydroxide ions: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.
pH ranges and universal indicator colours: 0–2 very acidic (red); 3–6 weakly acidic (orange/yellow); 7 neutral (green); 8–11 weakly alkaline (blue); 12–14 very alkaline (purple).
Ionic equation for neutralisation: H⁺(aq) + OH⁻(aq) → H₂O(l). H⁺ comes from the acid, OH⁻ from the alkali; the other ions are spectators.
Balance: Al(OH)₃ + HNO₃ → Al(NO₃)₃ + H₂O: Al(OH)₃ + 3HNO₃ → Al(NO₃)₃ + 3H₂O

Making a soluble salt from a metal or an insoluble base: Warm the acid; stir in the solid until some is left over (excess); filter off the excess; crystallise the filtrate.
Which metals are unsuitable for the metal + acid route, and why?: Potassium, sodium, lithium: too reactive — violent and dangerous. Copper, silver, gold: not reactive enough — no reaction with dilute hydrochloric or sulfuric acid.
Making a salt from an alkali and an acid: Pipette the alkali into a flask with indicator; add acid from a burette until the colour just changes; repeat with the same volumes and no indicator; crystallise.
Crystallisation: method: Heat to evaporate some water until saturated (crystals form on a cooled glass rod); cool slowly; filter, rinse with a little cold water and dry between filter papers. Do not heat to dryness.
Making an insoluble salt such as barium sulfate: Mix two solutions, e.g. barium nitrate and potassium sulfate; filter; wash the residue with distilled water; dry. Ba(NO₃)₂(aq) + K₂SO₄(aq) → BaSO₄(s) + 2KNO₃(aq)
How is precipitation used in water treatment?: To remove unwanted ions: calcium ions from hard water as calcium carbonate; metal ions from effluent as insoluble hydroxides; phosphate as an insoluble phosphate.