Chemistry Help
Acids, bases and indicators
Acids and bases were first thought as follows. An acid is a substance that tastes sour and a base is a substance that tastes bitter. Most acids and bases however, are NOT SAFE to taste.
A strong base is soluble in water and is called an alkali. Alkali solutions are caustic and can cause severe burns. Alkali solutions dissolve fats and are used as cleaning agents. Examples include cleaning products containing cloudy ammonia and oven cleaners which contain caustic soda or sodium hydroxide.
| Alkali (strong bases - soluble) | Bases (low solubility) | ||
| Name | Chemical formula | Name | Chemical formula |
| Sodium hydroxide | NaOH | Magnesium hydroxide | Mg(OH)2 |
| Potoassium hydroxide | KOH | Calcium hydroxide | Ca(OH)2 |
| Ammonia | NH3 | Aluminum hydroxide | Al(OH)3 |
The oxides of the Group I elements or alkali metals all dissolve in water to produce alkali solutions.
Eg. Sodium oxide + water → sodium hydroxide
Na2O + H2O → 2NaOH
Strong acids are corrosive in nature and dissolve active metals like magnesium, zinc and iron. examples of strong acids include sulfuric acid, hydrochloric acid and nitric acid.
| Name of acid |
Chemical formula |
| Hydrochloric acid | HCl |
| Nitric acid | HNO3 |
| Nitrous acid | HNO2 |
| Acetic acid | CH3COOH |
| Sulfuric acid | H2SO4 |
| Sulfurous acid | H2SO3 |
| Carbonic acid | H2CO3 |
| Phosphoric acid | H3PO4 |
Soluble non-metallic oxides dissolve in water to produce acidic solutions.
Eg. Water + carbon dioxide → carbonic acid
H2O + CO2 →H2CO3
Chemical indicators are substances that change color in the presence of an acid or base. They can be used to safely to help us determine if a substance is acidic or basic.
Examples of chemical indicators include litmus paper, phenolphthalein, bromothymol blue, methyl red and methyl orange. Litmus is pink in acidic solutions and blue is basic solutions.
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