CBSE Class 10 Science 2020 · Paper 31/3/3 · Question 26(a)

Metals and Non-metals 5 marks Medium

A metal ‘M’ is stored under kerosene. It vigorously catches fire, if a small piece of this metal is kept open in air. Dissolution of this metal in water releases great amount of energy and the metal catches fire. The solution so formed turns red litmus blue.

(a)Name the metal ‘M’.
(b)Write formula of the compound formed when this metal is exposed to air.
(c)Why is metal ‘M’ stored under kerosene ?
(d)If oxide of this metal is treated with hydrochloric acid, what would be the products ?
(e)Write balanced equations for : (i) Reaction of ‘M’ with air. (ii) Reaction of ‘M’ with water. (iii) Reaction of metal oxide with hydrochloric acid.

Answer

Metal M is sodium; it forms $Na_{2} O$ in air, is kept under kerosene to exclude air and moisture, and gives NaOH and hydrogen with water.

(a) The metal M is sodium (

Na

). (b)

Na_{2} O

(sodium oxide). (c) Sodium reacts so vigorously with the oxygen and moisture of air that it catches fire if kept in the open. Kerosene does not react with it and keeps air and moisture away, so accidental fires are prevented. (d) Sodium chloride and water (

NaCl

and

H_{2} O

). (e) (i)

4 Na (s) + O_{2} (g) ⟶ 2 Na_{2} O (s)

(ii)

2 Na (s) + 2 H_{2} O (l) ⟶ 2 NaOH (a q) + H_{2} (g) + heat energy

(iii)

Na_{2} O (s) + 2 HCl (a q) ⟶ 2 NaCl (a q) + H_{2} O (l)

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CBSE Class 10 Science 2020 · Paper 31/3/3 · Question 26(a)

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