Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture…
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
Answer the following questions :
(a) Solution P is a strong acid while solution Q is a strong base. On the pH scale, where would you place the solutions P and Q ? [1]
(b) A solution has a pH of 7. Name a compound you would use to (i) increase its pH, and (ii) decrease its pH. [1]
(c) (i) When the pH of a solution is decreased from 4 to 2, what effect does it produce on its hydronium ion concentration ? State the colour change shown by the pH paper. [2]
Solution
(a) P – pH 0 to 4
Q – pH 12 to 14
(b) (i) By adding sodium hydroxide (or any other base)
(ii) By adding hydrochloric acid (or any other mineral or strong acid)
(c) (i) • Hydronium ion (H3O+/H+) ion concentration increases.
• Colour will change from yellow/orange to red/pink
