Q53 of 65 Page 24

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.

A is Ca, B is Ca(OH)2 , C is CaO
Ca(s) + 2H2O → Ca(OH)2 + H2 (g)
Ca(OH)2 → CaO + H2O


Element A is calcium (Ca). When calcium reacts with water, it forms calcium hydroxide [Ca(OH)2]. Calcium hydroxide is used in white washing. Thus compound B is calcium hydroxide [Ca(OH)2]. Compound B on heating gives oxide of calcium (CaO). Thus, C is calcium oxide (CaO). Calcium oxide (CaO) on treatment with water gives back B [Ca(OH)2].


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