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+).
The oxides, hydroxides and carbonates of metals, such as
sodium hydroxide, are bases.
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.
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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.
Geranium plants grown
in acidic soil have red
flowers, while geraniums
grown in alkali soil have
blue flowers.
Universal indicator is a mixture of indicators. It is useful
because it shows a range of colours from pH 1–14.
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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.
What are the pH values of some everyday items?
1
2
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3
4
5
6
7
8
9
10 11 12 13 14
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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.
acid
+
base

salt
+
water
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.
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Naming salts
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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.
Water is formed because the oxygen and hydrogen from the
alkali react with the hydrogen from the acid to produce
molecules of water (H2O).
For example:
hydrochloric
acid
HCl (aq)
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+
sodium
hydroxide

sodium
chloride
+
water
+ NaOH (aq)  NaCl (aq) + H2O (l)
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Glossary
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Multiple-choice quiz
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