Q. 535.0( 5 Votes )

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.

Class 10th NCERT - Science Exemplar 3. Metals and Non-metals

Answer :

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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PREVIOUSName one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C).NEXTAn alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved.

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