A collective noun is a noun that can be singular in form whilst referring to a group of people or things. Collective nouns are sometimes confused with mass nouns.ome collective nouns can stand alone, such as Britain has an army, but if the collective noun army is used to mean something other than an organized military force, you can say things like an army of women or an army of ants, and even an army of one.
Rainwater is slightly acidic because the CO2 in the atmosphere is soluble in water (the water in the air). When in solution CO2 forms a weak acid (Carbonic acid) which makes pure rainwater a weak acid. 1 person found this useful.
A change of 1 unit on a pH scale represents a 10 fold change in the pH, so that water with pH of 6 is 10 times more acidic than water with a pH of 7, and water with a pH of 5 is 100 times more acidic than water with a pH of 7. You might expect rainwater to be neutral, but it is actually somewhat acidic.