4.4 define acids as sources of hydrogen ions, H+ , and alkalis as sources of hydroxide ions, OH¯

Acids and alkalis

An acid (at GCSE) is a substance that dissolves in water to produce hydrogen ions (H+)

An alkali is a substance that dissolves in water to produce hydroxide ions (OH-)

4.3 describe the use of universal indicator to measure the approximate pH value of a solution

Universal indicator can come in two forms, either in a liquid solution of ethanol or in a paper that has been soaked in the indicator solution.

Either drop some universal indicator into the solution or drop the liquid under test onto the paper.

4.2 understand how the pH scale, from 0–14, can be used to classify solutions as strongly acidic, weakly acidic, neutral, weakly alkaline or strongly alkaline