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Acids and Alkalis

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What are acids and alkalis?

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What are bases?

All alkalis are bases. Bases are substances that react with acids by absorbing hydrogen ions (H+).

Some bases are soluble in water. These are called alkalis.

All alkalis contain hydroxide ions (OH–). The more OH– ions in the solution, the stronger the alkali.

The oxides, hydroxides and carbonates of metals, such as sodium hydroxide, are bases.

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What are indicators?

Indicators are chemicals that change colour in the presence of an acid or an alkali.

There are many different indicators. Lots of them come from plants, like red cabbage. Different indicators turn different colours.

Universal indicator is a mixture of indicators. It is useful because it shows a range of colours from pH 1–14.

Geranium plants grown in acidic soil have red flowers, while geraniums grown in alkali soil have blue flowers.

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What does the pH scale show?

The pH scale runs from 1 to 14. The numbers 1 to 6 represent acidic conditions and 8 to 14 represent alkali conditions. A pH value 7 is neutral.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

What are the pH values of some everyday items?

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What does the pH scale show?

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What is the order of pH?

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Acids and bases – true or false?

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Making salts

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pH change during neutralization

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How are salts made and named?

When an acid reacts with a base, a neutralization reaction occurs and produces a chemical called a salt.

The name of the salt depends on the names of the reactants.

The first part of the salt’s name comes from the metal in the base: e.g. sodium hydroxide sodium…

The second part of the salt’s name comes from the acid: e.g. sulfuric acid …sulfate

For example, if sodium hydroxide neutralizes sulfuric acid, the product is a salt called sodium sulfate.

+acid base salt + water

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Naming salts

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Water is formed because the oxygen and hydrogen from the alkali react with the hydrogen from the acid to produce molecules of water (H2O).

Making salts with an acid and an alkali

When an acid reacts with an alkali, H+ ions from the acid and OH- ions from the alkali combine to produce a salt and water.

For example:

+ +

++

sodiumhydroxide

NaOH (aq)

sodiumchloride

NaCl (aq)

water

H2O (l)

hydrochloricacid

HCl (aq)

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Glossary

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Multiple-choice quiz