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Acids, alkalis and neutralisation
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Lemon juice is acidic and soap is alkaline. The pH scale tells us how acidic or alkaline something is.
The pH scale and indicators
pH runs from 0 to 14. Below 7 is acidic, 7 is neutral, above 7 is alkaline.
An indicator changes colour depending on pH.
Universal indicator: red or orange in acids, green when neutral, blue or purple in alkalis.
Litmus: red in acids, blue in alkalis.
An indicator changes colour depending on pH.
Universal indicator: red or orange in acids, green when neutral, blue or purple in alkalis.
Litmus: red in acids, blue in alkalis.
Neutralisation
An alkali is a base that dissolves in water. Acids and alkalis neutralise each other.
acid + alkali → salt + water
The salt's name comes from the acid: hydrochloric acid makes chlorides, sulfuric acid makes sulfates, nitric acid makes nitrates.
Example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
acid + alkali → salt + water
The salt's name comes from the acid: hydrochloric acid makes chlorides, sulfuric acid makes sulfates, nitric acid makes nitrates.
Example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
Acids and metals
Many metals react with acids:
metal + acid → salt + hydrogen
Example: magnesium + hydrochloric acid → magnesium chloride + hydrogen.
Test for hydrogen: a lit splint gives a squeaky pop.
metal + acid → salt + hydrogen
Example: magnesium + hydrochloric acid → magnesium chloride + hydrogen.
Test for hydrogen: a lit splint gives a squeaky pop.
Name the salt made when sulfuric acid reacts with sodium hydroxide.
- Sulfuric acid makes sulfates.
- The metal from the alkali is sodium.
Answer: Sodium sulfate (plus water).
pH below 7 is acidic, 7 neutral, above 7 alkaline. Acid + alkali → salt + water. Metal + acid → salt + hydrogen (squeaky pop). Hydrochloric acid makes chlorides, sulfuric makes sulfates, nitric makes nitrates.
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