Here's how it works:
* pH meters measure the hydrogen ion concentration (H+) in a solution.
* Acidity is determined by the concentration of H+ ions: higher concentration = higher acidity.
* Rainwater is naturally slightly acidic due to the presence of carbon dioxide in the atmosphere, which dissolves into carbonic acid.
* Acid rain has a pH lower than 5.6, indicating a higher concentration of H+ ions.
Therefore, a pH meter is used to measure the pH of rainwater and determine its acidity level.
