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Acids, alkalis and pH
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From stomach acid to oven cleaner, acids and alkalis are everywhere. The pH scale tells you how acidic or alkaline something is.
The pH scale
The pH scale runs from 0 to 14.
Below 7: acidic. 7: neutral. Above 7: alkaline.
The lower the pH, the more acidic the solution.
Below 7: acidic. 7: neutral. Above 7: alkaline.
The lower the pH, the more acidic the solution.
Ions in solution
Acids produce hydrogen ions, H+, in water.
Alkalis produce hydroxide ions, OH−, in water.
An alkali is a base that dissolves in water.
Alkalis produce hydroxide ions, OH−, in water.
An alkali is a base that dissolves in water.
Indicators
Indicators change colour depending on pH.
A solution turns phenolphthalein pink. Is it acidic or alkaline?
- Phenolphthalein is colourless in acid.
- It turns pink in alkali.
- So the solution is alkaline.
Answer: Alkaline
pH below 7 is acidic, 7 neutral, above 7 alkaline. Acids release H+ ions, alkalis release OH− ions. Indicators show which by changing colour.
The interactive lesson includes the diagrams for this topic.
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