Chemistry (school) · Part 06
Acids, bases and salts
How acids and alkalis behave, how to measure them and how salts are made.
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- AcidA substance that forms hydrogen ions (H+) when it dissolves in water. Acids have a pH below 7 and taste sour.
- AlkaliA base that dissolves in water and forms hydroxide ions (OH-). Alkalis have a pH above 7 and feel soapy.
- pH scaleA scale from 0 to 14 showing how acidic or alkaline a solution is. Below 7 is acid, 7 is neutral and above 7 is alkaline.
- IndicatorA dye that changes colour depending on whether a solution is acidic or alkaline. Universal indicator gives a range of colours that match the pH.
- NeutralisationThe reaction between an acid and an alkali (or base) that makes a salt and water. The pH moves towards 7.
- SaltA compound made when the hydrogen of an acid is replaced by a metal. The name comes from the metal and the acid used.
- Strong and weak acidsA strong acid fully splits into ions in water. A weak acid only partly splits. Strength is different from concentration.
- TitrationA careful method that finds out exactly how much acid is needed to neutralise a measured amount of alkali, using a burette and an indicator.
- Metal and acid reactionA reactive metal reacts with an acid to make a salt and hydrogen gas. The fizzing is hydrogen forming.