How to Measure the Acidity of Rain

Acidity of a solution is expressed using a pH scale with a pH of 7 corresponding to a neutral media. Lower pH values are indicative of acidic solution. Natural rainwater is slightly acidic with a pH around 5.6. However, heavy air pollution with sulfur and nitrogen dioxides may lead to acid rains with pH lower than 3. A simple way to measure the rain acidity is to use pH paper indicators that change color based upon a pH value.

Things You'll Need

• Small Beaker, 10 ml
• Hydrion pH paper

Instructions

1. When it is forecast to rain, place the beaker outside and collect about 5 ml of the rainwater.

2. Detach a strip of the hydrion pH paper.

3. Holding one end of the pH paper strip, put the other end into the rainwater and take it out after one to two seconds. The part of the paper that was in the water should change color.

4. 

   Compare the color of the paper with the scale printed on the pH paper pack. Assign pH accordingly (see figure).

Resources

• Acid Rain
• Hydrion pH paper