(a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?(b) Dry hydrogen chloride gas does not change the colour of dry litmus paper why?

(a) The dilution of acid is an exothermic reaction, so on adding acid to water the heat that evolved gets absorbed by the water but if the water is added to acid a large amount of heat is evolved leading to a spill of acid which may cause severe burns.

(b)  Dry HCl does not change the colour of dry litmus paper because dry HCl does not undergo dissociation to form ions as there is an absence of an aqueous medium. The colour of the litmus paper changes only when the ions are formed. Hence it does not change the colour of litmus paper.

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Updated on: 10-Oct-2022

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