Question

An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.

Answer 1

A is calcium, B is calcium hydroxide and C is calcium oxide.

`"Ca"("s") + 2"H"_2"O"("l") -> "Ca"("OH")_2("aq") + "H"_2("g")`

`"Ca"("OH")_2("s")overset("Heat")(->) "CaO"("s") + "H"_2"O"("g")`

`"CaO"("s") + "H"_2"O"("I") -> "Ca"("OH")_2("aq")`