Acids, Bases and Salts
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What is meant by neutrality, acidity, and alkalinity in terms of pH?
Neutrality = pH 7, Acidity = pH < 7, Alkalinity = pH > 7. Measured using universal indicator.
What are the characteristic properties of acids?
• turn blue litmus red • react with metals —> hydrogen gas • react with bases —> salts and water • react with carbonates —> carbon dioxide
Must know acids
• HCl • H₂SO₄
What are the characteristic properties of bases?
• turn red litmus blue • react with acids —>salts and water • soluble bases are called alkalis • react with ammonium salts —> produce ammonia gas, water, and salt (when heated)
Common alkalis
• Sodium hydroxide (NaOH) • potassium hydroxide (KOH) • ammonia solution (NH₃)aq.
How do acids and bases differ in terms of protons (H⁺)?
• Acids donate protons (H⁺ ions) • Bases accept protons
Why is it important to control soil acidity?
To ensure optimal plant growth — too acidic soil can be neutralised using bases like limestone (calcium carbonate).
What are nonmetal oxides
Acidic
what are metal oxides
basic
What are neutral oxides
Oxides that are neither acidic nor basic - carbon monoxide (CO), water (H₂O)
What are amphoteric oxides
Oxides that can act as both acidic and basic - aluminium oxide (Al₂O₃), zinc oxide (ZnO).
Methods to prepare salts
Neutralisation, precipitation, and titration
How are salts purified?
By filtration, washing, and crystallisation.
How would you prepare an insoluble salt?
By mixing two soluble salts to form an insoluble product (precipitation method)
How would you prepare a soluble salt from an acid and an insoluble base or carbonate?
Add excess base to the acid, filter off the unreacted solid, and evaporate the filtrate to obtain crystals
What cations can be identified using aqueous sodium hydroxide or ammonia?
Ammonium, calcium, copper(II), iron(II), iron(III), and zinc
What test identifies lithium, sodium, potassium, and copper(II) ions?
Flame tests: Lithium: crimson red Sodium: yellowy-orange Potassium: lilac Copper(II): blue-green
How is carbonate ion identified?
Add dilute acid → effervescence → gas turns limewater milky (CO₂)
How are chloride and bromide ions identified?
Add aqueous silver nitrate under acidic conditions: Chloride → white precipitate Bromide → cream precipitate
How is sulfate ion identified?
Add barium nitrate or barium chloride under acidic conditions → white precipitate of barium sulfate forms
How is nitrate ion identified?
Heat with aluminium and sodium hydroxide → ammonia gas produced (pungent smell, turns damp red litmus blue)
ammonia gas test
Turns damp red litmus paper blue
carbon dioxide gas test
Turns limewater milky
chlorine gas test
Turns damp blue litmus red and then bleaches it white