acid and bases

acids

• produces H+ ions in aqueous solutions

properties:

• pH 0-6

• contains H+ ions

• turns damp blue litmus paper red

• metal + acid → salt + hydrogen

test for hydrogen gas: lighted splint extinguished with a ‘pop’ sound

• metal carbonate + acid → salt + water + carbon dioxide

test for carbon dioxide gas: bubble gas through limewater and if gas present, white precipitate formed

• metal hydroxide/ oxide + acid → salt + water (neutralisation)

strength of acid: extent of dissociation when dissolved in water

• strong acids: fully dissociate in water

• weak acids: partially dissociate in water

bases

• metal hydroxides or oxides, produces OH- ions when dissolved in aqueous solutions

• alkalis are bases that are soluble in water e.g. sodium hydroxide, calcium hydroxide, aqueous ammonia

properties of alkalis:

• contains OH- ions

• feel soapy and slippery

• turns red litmus paper blue

• pH 8-14

• alkali + acid → salt + water (neutralisation)

• alkali + ammonium salt → salt + ammonia + water

test for gas: turns damp red litmus blue and produces a pungent smell

controlling acidity of soil

• when soils are too acidic, quicklime (calcium oxide) or slaked lime (calcium hydroxide) can be added to soils

• ammonium salt (ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium carbonate) should not be added as ammonia gas will be formed which is very light and can easily escape decreasing nitrogen content for plants

oxides of metal

• basic oxide

- metal oxides that only react with acids e.g. MgO, CaO

• acidic oxide

- non metal oxide that only react with bases e.g. CO2, SO2

• amphoteric acid

- metallic oxide that reacts with both acid and bases e.g. ZnO, Al2O3, PbO

• neutral oxide

- monoxides that do not react with acids or bases e.g. CO, NO, H2O