What happens to rainwater to make it more acidic than usual?
The pH value of unpolluted rainwater is usually slightly below 7. This is because carbon dioxide in the air dissolves in rainwater to form carbonic acid, which is a weak acid.
Pure rain water with no dissolved minerals has a PH of 7, that makes it neutral. When water has certain substances that lower the PH below 7, it is considered to be acidic. Dissolved polyatomic ions make the rain acidic. These polyatomic ions can come from the products of a cumbustion reaction (CH4 + O2 --Energy Source--> CO2 + H2O)
H2O, hydrogen and oxygen. Photosynthesis in plants combines hydrogen from water with carbon from CO2 (carbon dioxide) in the atmosphere to make carbohydrates, or simple sugars and starches. The carbohydrates fuel plant growth and feed the plants--and us. The slightly acidic level of rainwater helps the vegetation absorb the nutrients in the soil. Rainwater does not contain chlorine or fluoride, so therefore is better for your plants than regular tap water.
Rainwater is slightly acidic (carbonic acid) because carbon dioxide from the atmosphere is dissolved in the water as it falls from the clouds Some rocks are alkaline, like the calcium carbonate that make up lime stone is dissolved. Gradually these cracks become deeper (grikes) forming a limestone pavement