Acid rain changes soil and water chemistry, which can stop seeds from growing. In this experiment, you test whether higher acid levels reduce carrot seed germination rates.

When harmful gases mix with rainfall, they form a weak acid that slowly eats away at stone. Marble buildings and sculptures are especially vulnerable — they lose mass over time as the acid dissolves the surface. This experiment tests whether a calcium oxalate coating can protect marble tiles from that damage. Three tiles each weigh 100 grams at the start. One gets no coating, one gets a commercial sealant, and the third gets a coat of oxalic acid that reacts with the marble to form calcium oxalate. All three soak in vinegar for five days while you track the weight each day. The uncoated tile loses the most mass. The calcium oxalate tile and the sealant tile both hold up much better, showing how a protective layer can slow the damage acid causes to stone surfaces.

How acidic does rain need to get before sunflower seeds stop growing entirely? To find out, you water five pots of sunflower seeds with water at pH levels ranging from pH 6 — close to normal rain — down to pH 2, which is very acidic. You measure the average height of three plants in each pot every two days for two weeks. At pH 6 and pH 5, plants grow normally. At pH 4, growth slows down sharply. At pH 3 and pH 2, the seeds never sprout at all. The results show a clear threshold: below a certain pH, the acid in the water shuts down germination completely.