f.3 Chemistry Questions

Question

(a)Explain why sculptures made of marble are usually corroded faster in heavily polluted areas? (Hint: acid rain)

(b)Explain what happens when a piece of marble is burnt in a non-luminous Bunsen flame.

(c) 'A piece of chalk can be turned into a metal,'a student claimed.Comment on his statement.

Answer 1

a.
in the acid rain, there're acids like sulphuric acid, sulphorous acid, nitric acid and nitrous acid. they can react with calcium carbonate (main component of marble) to form carbon dioxide, water and the calcium salts, which are quite soluble in water. then the rain water will wash away the salts, and the new surface is attacked again and again... thus the sculptures are easily corroded.

b.
although the temp. is not high enough to break down calcium carbonate, remember there's calcium ion! thus a brick red flame will be observe.

c.
he's correct. first, heat the calcium carbonate in chalk strongly, so that it decomposes to form calcium oxide. con't heating until it melts. then, electrolyse the molten calcium oxide, so the calcium can be obtained at the cathode.

Answer 2

1. What is marble? Calcium carbonate + acid rain (H2SO4 / HNO3) - CaSO4 / Ca(NO3)2 + CO2 + H2O

2. nothing happen since the temp of non-luminous bunsen flame is not high enough to breakdown CaCO3 to CaO & CO2

3. What is Chalk? It is also CaCO3, how to get back Calcium? It is the time for you to research in Lab / Lib. ^^