A solid substance P which is very hard is used in the construction of many buildings, especially flooring. When substance P is heated strongly, it decomposes to form another solid Q and a gas R is given out. Solid Q reacts with water with the release of a lot of heat to form a substance S. When gas R is passed into a clear solution of substance S, then a white precipitate of substance T is formed. The substance T has the same chemical composition as starting substance P.
(a) What is substance P? Write its common name as well as chemical formula.
(b) What is substance Q?
(c) What is gas R?
(d) What is substance S? What is its clear solution known as?
(e) What is substance T? Name any two natural forms in which substance T occurs in nature.

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Solution

(a) Substance P is calcium carbonate. Its common name is limestone and its chemical formula is CaCO₃.

(b) Substance Q is calcium oxide (CaO).

(c) Gas R is carbon dioxide gas (CO₂).

(d) Substance S is calcium hydroxide [Ca(OH)₂]. Its clear solution is known as lime water.

(e) Substance T is calcium carbonate (CaCO₃). Two natural forms of calcium carbonate are calcite and mollusc shell.

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