A naturally occurring minerals of sedimentary rocks on heating to high temperatures decomposes giving a solid 'A' and a gas. The solid on dissolution in water undergoes chemical reactions which is associtated with hissing sound and the solution appears to be boiling. Compound 'B' formed during this reaction on long standing forms a layer of white powder. When excess CO_(2) is passed through this milky white solution, a clear solution is formed again. Identify the substances and justify the above observations. Give reasons wherever required.

A naturally occurring minerals of sedimentary rocks on heating to high

1.	A naturally occurring minerals of sedimentary rocks on heating to high temperatures decomposes giving a solid 'A' and a gas. The solid on dissolution in water undergoes chemical reactions which is associtated with hissing sound and the solution appears to be boiling. Compound 'B' formed during this reaction on long standing forms a layer of white powder. When excess CO_(2) is passed through this milky white solution, a clear solution is formed again. Identify the substances and justify the above observations. Give reasons wherever required.
Answer» Solution :Limestone is the naturally OCCURRING mineral in sedimentary ROCKS. This contains calcium carbonate which on decomposition at high TEMPERATURE gives solid CaO and `CO_(2)`. CaO on reaction with water forms `Ca(OH)_(2)`. This is highly exothermic reaction and `CO_(2)` gas is evolved during this reaction. THEREFORE, the solution appears to be BOILING and is associated with hissing sound. On long exposure to air, this reacts with atmospheric `CO_(2)` to form `CaCO_(3)` as a white powdered layer. On passing excess `CO_(2),CaCO_(3)` reacts with this forming soluble calcium bicarbonate. Therefore, a clear solution is formed again.