Question

With the help of labelled diagrams, describe an activity to show that acids produce ions only in aqueous solutions.

Answer 1

1. Take about 1 g of solid sodium chloride (NaCl) into a clean, dry boiling tube and add some concentrated sulphuric acid to it very carefully [see figure]. Fit a rubber cork with a small glass delivery tube in the mouth of the boiling tube, as shown in the figure. Concentrated sulphuric acid reacts with sodium chloride to form hydrogen chloride gas. Hydrogen chloride gas begins to escape from the open end of the glass tube.
2. Hold a dry blue litmus paper in hydrogen chloride gas [see figure]. There is no change in the colour of dry blue litmus paper. This shows that hydrogen chloride gas (HCl) does not behave as an acid in the absence of water (there is no water on dry litmus paper).
3. We now hold a moist (or wet) blue litmus paper in hydrogen chloride gas [see figure]. We will see that the moist blue litmus paper turns red. This shows that hydrogen chloride gas (HCl) exhibits acidic behaviour in the presence of water (as present in moist or wet litmus paper).