Question

(a) What effect does the concentration of H⁺ (aq) ions have on the nature of a solution?
(b) What effect does the concentration of OH⁻ ions have on the nature of a solution?
(c) Someone put some universal indicator paper into vinegar. The pH is 3. What does this tell you about the vinegar?
(d) Someone put some universal indicator paper onto wet soap. The pH is 8. What does this tell you about the soap?
(e) State whether a solution is acidic, alkaline or neutral if its pH is:
(i) 9
(ii) 4
(iii) 7
(iv) 1
(v) 10
(vi) 3

Answer 1

(a) Acids furnish hydrogen ions (H⁺ ions) when dissolved in water. The more will be the concentration of H⁺ ions in a solution, the lower will be its pH. Thus, an increase in the concentration of H⁺ ions in a solution leads to increase in the acidity of the solution.

(b) Bases furnish hydroxide ions (OH^- ions) when dissolved in water. The concentration of hydroxide ions increases as bases dissolve in water. With the increase in the concentration on OH^- ions, the pH also increases, thus, strengthening the basic nature of the solution.

(c) Universal indicator paper dipped into vinegar shows pH 3, indicating that vinegar is an acid. Acids show a value below 7 on the pH scale.

(d) Universal indicator paper put onto wet soap shows pH 8, indicating that wet soap is a base. Bases show a value above 7 on the pH scale.

(e) We know that solutions that have pH values less than 7 (from 0) are acidic, those with pH greater than 7 (up to 14) are basic (or alkaline) and those with pH 7 are neutral. The lower the pH, the higher the acidity, and the higher the pH, the higher the basicity. Let us classify solutions with the given pH values as acidic, alkaline or neutral.

The pH of the solution	Nature of the solution
(i) 9	Basic
(ii) 4	Acidic
(iii) 7	Neutral
(iv) 1	Acidic
(v) 10	Basic
(vi) 3	Acidic