Question

Give suitable reasons for the following statements :
(a) Rain water conducts electricity but distilled water does not
(b) We feel burning sensation in the stomach when we overeat.
(c) A tarnished copper vessel regains its shine when nabbed with lemon.
(d) The crystals of washing soda change to white powder on exposure to air.
(e) An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.

CBSE Class X Science LA (5 Marks)

Answer 1

(a) Distilled water does not conduct electricity because it does not contain any ionic compound like acids, bases or salts dissolved in it.

(b) When we overeat, excess of acid is produced in the stomach which causes burning sensation.

(c) Copper vessels tarnish due to formation of basic copper carbonate which gets neutralized when rubbed with lemon and the copper vessel regains its shine.

(d) Washing soda is sodium carbonate decahydrate which when exposed to air lases 10 molecules of water and changes to white powder.

(e) Sodium chloride is a salt of strong acid HCl and strong base NaOH, so it is neutral. Sodium carbonate is a salt of weak acid H2CO3 and strong base NaOH, so it is basic

Answer 2

1. RAIN WATER HAS MANY SALT CONTENTS IN IT WHICH HELPS IT CONDUCT ELECTRICITY.

DISTILLED WATER ACTS AS AN INSULATOR AND WILL THUS HAVE A VERY HIGH RESISTANCE .

2) We feel burning sensation when we overeat because at that point of time more HCl is secreted in order to digest the food faster which acidic in nature and therefore we feel burning sensation.

3.COPPER CARBONATE CaCO3 IS BASIC IN NATURE , LEMON IS ACIDIC THUS , LEMON NEUTRALISES THE COPPER CARBONATE.

4.WATER OF CRYSTALLISATION EVAPORATES AND THE WASHING SODA BECOMES ANHYDROUS.

5)the pH value of the two solutions differ from each other that is the reason sodium chloride is neutral and sodium carbonate is basic.

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