Question

Describe an experiment to prove the following:
HCI is highly soluble in water.

Answer 1

The high solubility of HCI gas can be demonstrated by "Fountain experiment''. In it, a well dried round bottom flask is filled with dry HCI gas and fitted with a two holed rubber stopper. A jet tube is inserted into the flask through one of the holes. A dropper filled with water is fitted into the other hole. Closing the outer end of the jet tube, the flask is inverted and the tube is dipped into a blue litmus solution taken in a beaker, then dropper is pressed. It is seen that the blue litmus solution enters the jet tube with a great force, forming a red fountain

It happens because water introduced from dropper completely absorbs HCI gas, thereby creating a very low pressure within the flask. To make up for this loss in pressure, blue litmus solution rises in the jet tube and colour of litmus changes to red.