Does rain have the same acidity everywhere in your neighborhood? Normal rain is slightly acidic. Pollution from cars and factories can make it even more acidic. You collect rainwater in a small cup each time it rains. You test the pH with a test strip and bring the strip to class. Everyone pins their strips on a neighborhood map at the spot where they collected. Over several rainy days, the map fills up with data from many locations. You compare pH readings across the neighborhood. Did some areas have more acidic rain? Did the acidity change over the weeks? The patterns may point to local pollution sources.