Lesson 1-Acid and base properties and indicators
Lesson Notes
Acid and base properties and indicators
Acids
| Acid | Formula | Uses |
| Hydrochloric acid | HCl | Stomach acid Swimming pool acid |
| Sulphuric acid | H2SO4 | Extraction of gold Dehydrating agent Production of fertilisers |
| Nitric acid | HNO3 | Production of fertilisers Explosives |
| Phosphoric acid | H3PO4 | Dental cement Flavour in fizzy cool drinks |
| Carbonic acid | H2CO3 | Fizzy drinks |
| Ethanoic acid | CH3COOH | Vinegar |
| Oxalic acid | COOHCOOH | Bleaching agent |
Acids found in nature: acetic acid, oxalic acid, citric acid, lactic acid, ascorbic acid
Mineral/inorganic acids: hydrochloric acid, sulphuric acid, nitric acid and phosphoric acid
Properties:
•Sour tasting
•Neutralises a base and forms a salt and water
•Releases hydrogen ions when dissolved in water and forms hydronium ions
•pH
•Conducts electricity in aqueous solutions
•Changes the colour of indicators
•Reacts with metals to form a salt and hydrogen gas
•Reacts with a carbonate to form a salt and carbon dioxide gas
Bases
| Base | Formula | Uses |
| Sodium hydroxide (caustic soda) | NaOH | Manufacturing of soap |
| Potassium hydroxide | KOH | Preparation of biodiesel |
| Ammonia | NH3 | Cleaning agent |
| Sodium carbonate | Na2CO3 | Production of glass |
| Sodium bicarbonate | NaHCO3 | Raising agent |
| Calcium carbonate | CaCO3 | Manufacturing of cement |
| Calcium hydroxide | Ca(OH)2 | Neutralises acidic soil |
| Magnesium hydroxide | Mg(OH)2 | Antacids for heartburn |
Properties:
•Soapy feeling
•Tastes bitter
•Neutralises an acid
•Changes colours of indicators
•Dissociates (breaks down) into hydroxide ions when dissolved in water
•When soluble in water, it is called an alkaline
•Alkalines conduct electricity in aqueous solutions
•pH > 7
Indicators
An indicator is a substance that undergoes colour changes depending on whether it has been added to an acid or a base.
Most commonly used indicators in the laboratory:
| Indicator | Colour in acid | Colour in base |
| Methyl orange | Orange | Yellow |
| Methyl red | Red | Yellow |
| Litmus | Red | Blue |
| Bromothymol blue | Yellow | Blue |
| Phenolphthalein | Colourless | Bright Pink |
Blue litmus paper is used to test for an acid. It turns red in the presence of an acid.
Red litmus paper is used to test for a base. It turns blue in the presence of a base
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