Bases and Alkalis

Base is any metal oxide or hydroxide.
Base contains either oxide or hydroxide ions
Base can also be defined as a substance which reacts with acid to give a salt and water only.
General equation for this reaction:
base + acid -> salt + water

Alkalis are a special class of bases
Alkali is a use that is soluble in water.
E.g. sodium hydroxide
Properties:
- Bitter taste and soapy feel
- Turn red litmus paper blue
- All alkalis produce hydroxide ions when dissolved in water
- Alkalis can react with acids to form a salt and water only
   - Reaction called: Neutralisation
- Alkalis heated with ammonium salts give off ammonia gas.
General equation for this reaction:
alkali + ammonium salt -> ammonia + water + salt
- Alkalis react with a solution of one metal salt to give metal hydroxide and another metal salt.
General equation for this reaction:
alkali + salt (of Metal A) => metal + salt (of Metal B) hydroxide

Uses:
Ammonia solution
- Window cleaning solution
- Fertilisers
Calcium oxide
- Neutralising acidic soil
- Make iron, concrete and cement
Sodium hydroxide
- Soaps and detergents
- Industrial-cleaning detergents
Magnesium hydroxide
- Neutralise acid on teeth (Toothpaste)
- Relieve indigestion (antacids)