The aim of the experiment is to find out which factors affect the decomposition of marble buildings by acid rain. This is the rate of reaction.

BACKGROUND KNOWLEDGE
ACID RAIN:
Acidity is measured using a pH scale, with the number 7 being neutral. A substance with a pH value of less than 7 is acidic, while one of a value greater than 7 is basic. The pH scale is logarithmic; that is, a substance of pH of 6 is 10 times more acidic than another with a pH of 7. Generally, the pH of 5.6 has been used as the baseline in identifying acid rain. Acid ran is defined as any rainfall that has an acidity level beyond what is expected in non-polluted rainfall. In essence, any precipitation that has a pH value of less than 5.6 is considered to be acid precipitation. This is a visual illustration of the pH scale:

One of the main causes of acid rain is sulphur dioxide. Natural sources that emit this gas are volcanoes, sea spray, rotting vegetation and plankton. However, the burning of fossil fuels, such as coal and oil, are largely to be blamed for approximately half of the emissions of this gas in the world. When sulphur dioxide reaches ...