Question

The pH value of pure water is 7. Compare the pH values of (i) Sulphur dioxide solution and (ii) Ammonia solution with that of pure water.

Answer 1

1. pH of the water

Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ dissociates into hydrogen $\left({\mathrm{H}}^{+}\right)$ and hydroxide $\left({\mathrm{OH}}^{-}\right)$ ions. Hence, it is a neutral substance having a pH of 7. If the nature of any solution is known, a specific range of pH can be predicted for that solution.

2. Explanation of pH values

(i) Sulphur dioxide $\left({\mathrm{SO}}_2\right)$ is a non-metal oxide, and solutions of such oxides are acidic in nature. Since acids have a low pH value, so Sulphur dioxide will have a pH of less than 7.

(ii) Ammonia $\left({\mathrm{NH}}_3\right)$ solution is alkaline in nature. Since bases have a high pH value, so Ammonia solution will have a pH of more than 7.