(a) A solution has a pH of 7. Explain how you would you:

(i) increase its pH

(ii) decrease its pH

(b) If a solution changes the colour of the litmus from red to blue, what can you say about its pH?

(c) What can you say about the pH of a solution that liberates carbon dioxide from sodium carbonate?

(a) The solution with pH 7 is neutral. Its pH can be increased by adding a small amount of base like sodium hydroxide. Basic solutions have pH more than 7. Similarly, pH can be decreased by adding small amount of acid like hydrochloric acid. Acidic solutions have pH less than 7.

(b) The change in colour of litmus from red to blue indicates that the solution is of basic nature with pH
more than 7.

(c) Carbon dioxide can be liberated by reacting sodium carbonate solution with acid like dilute hydrochloric acid. This shows that the solution is of acidic nature with pH less than 7.