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Acids, bases and metals

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Bases and alkalis

Bases v alkalis

Bases are substances that react with acids and neutralise them. They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates. Many bases are insoluble - they do not dissolve in water.

If a base does dissolve in water, we call it an alkali.

Here are two examples:

  • Copper oxide is a base because it will react with acids and neutralise them, but it is not an alkali because it does not dissolve in water.

  • Sodium hydroxide is a base because it will react with acids and neutralise them. It's also an alkali because it dissolves in water.

Shows a large red circle representing bases. Within this is a smaller grey circle representing alkalis.

All alkalis are bases, but only soluble bases are alkalis

Bases in the laboratory

You will have used some strong bases and alkalis at school, such as sodium hydroxide solution. Like acids, their bottles are labelled with the warning symbol for 'irritant'. This means that they will 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.

Concentrated alkalis are corrosive. They can attack metals and destroy skin if spilled. They are just as dangerous as concentrated acids, but many people do not realise this.

Bases in the home

Bases react with oils and fats, so they are often used in strong household cleaners. Drain cleaners and oven cleaners usually contain sodium hydroxide for example. And ammonia is also commonly used in cleaners. Ammonia 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.

Activity

Acids, bases and metals activity

Handle with care! Toxic revision material.

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