中一科學問題 (英文)

I have to regret that I only know the answer for question 3.
(3): Soil is usually acidic, as normal rain has a pH of 5.6, and rain with a pH lower than 5.6 is considered as acid rain. The reason that soil is mostly acidic are mainly:
rotten vegetation (bacteria in the soil)
acid rain
use of fertilizer (fertilizer is acidic)

In order to neutralize the soil, calcium carbonate (limestone) or calcium hydoxide (slaked lime) should be added to the soil.

Source of limestone and slaked lime (By chemical reaction)
Extract calcium carbonate from rocks in the nature,for example electrolysis,limestone can be otained.

If want to obtain slaked lime, burn limestone with a Bunsen flame, calcium oxide and carbon dioxide are produced. (CaCO3---Cao+CO2)

Dissolve calcium oxide (quick lime) into water, calcium hydoxide(slaked lime) can then be obtained.