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Bases v alkalis

A base is a substance that can react with acids and neutralise them. Bases are usually:

• metal oxides, such as copper oxide
• metal hydroxides, such as sodium hydroxide, or
• metal carbonates, such as calcium carbonate

Many bases are insoluble - they do not dissolve in water. However, if a base does dissolve in water, we also call it an alkali.

The table shows two examples of bases:

Bases in the laboratory

Household cleaning products contain strong bases, such as sodium hydroxide solution. Like acids, their bottles are labelled with a symbol to warn that they may make your skin red or blistered unless you wash off any spills with plenty of water.

Alkalis feel soapy when they get on your skin, so it is easy to tell when you have had an accident and must wash your hands.

Just like concentrated acids, concentrated alkalis are corrosive. They can attack metals and destroy skin if spilled, so their containers are labelled with a warning symbol. Concentrated alkalis are just as dangerous as concentrated acids, sometimes more dangerous, but many people do not realise this.

Bases in the home

Bases react with oils and fats, so they are often used in household cleaners. For example, drain cleaners and oven cleaners usually contain sodium hydroxide. Ammonia is also commonly used in cleaners, and it can be recognised by its choking smell.

It is wise to wear gloves when using these substances, otherwise they will react with your skin and burn it.

Weak bases and alkalis are found in toothpaste, antacid tablets (to help cure an upset stomach) and baking powder.