Give reasons :

1. In the laboratory preparation of HCL acid from NACL and conc H2SO4 , the residual salt formed at temperatures above 200 °C forms a hard crust and stick to the glass. [2]

2. In the fountain experiment to demonstrate the high solubility of HCL gas in water , dry HCL gas is filled in the round bottom flask. [2]

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Solution

(1)The reaction proceeds as,
H2SO4 + 2 NaCl -------> 2 HCl + Na2SO4

Formation of hard crust of Na2SO4 which sticks to glass

(2)When the HCl gas dissolves, water is sucked up to create a fountain, this creates a lot of vacuum which may lead to imploding of the flask. In Round Bottom Flask the pressure is equally distributed and hence is safer to conduct the experiment.

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