Passage I

Marble, which can be used to make buildings, is composed mostly of calcium carbonate. Marble is corroded (broken down) by air pollutants such as fly ash, nitric acid, and sulfuric acid.

· Fly ash contains corrosive materials.

· Nitric acid, produced when nitrogen dioxide reacts with water, reacts with calcium carbonate to form calcium nitrate.

· Sulfuric acid, produced when sulfur dioxide reacts with air and water, reacts with calcium carbonate to form calcium sulfate.

A scientist studied marble corrosion.

Experiment 1

The scientist measured the initial mass of 4 samples from the same piece of marble. Each sample had a surface area of 24 square centimeters (cm²). The scientist placed each sample in a separate container and added an acid solution (acid and water) with an acid concentration of either 30 parts per million (ppm) or 100 ppm. After 24 hours, the scientist removed each sample, scraped off the calcium nitrate or calcium sulfate, and measured the final mass of the sample. The scientist determined the mass of marble lost from each sample, in milligrams (mg), as shown in Table 1.

Experiment 2

The scientist obtained marble samples from buildings of different ages. The outer surface of each sample had a gray crust of calcium sulfate, calcium nitrate, and fly ash. The concentrations of calcium sulfate and calcium nitrate in the crust were determined, as shown in Table 2.