Ionic Equilibrium Acids and Bases - UNSOLVED PRACTICE SET

Q7. Define acids and bases according to the Arrhenius concept. Give one limitation of this concept.

Q8. Explain the Brønsted-Lowry concept of acids and bases. Identify the conjugate acid-base pairs in the reaction:

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

Q9. What is meant by the ionic product of water (Kw)? Write its value at 25°C. How does Kw change with temperature?

Q10. A student measures the pH of lemon juice as 2.5 and the pH of milk as 6.5. Calculate the ratio of H⁺ ion concentrations in lemon juice to that in milk.

Q11. Explain why pure water is considered both a very weak acid and a very weak base according to the Brønsted-Lowry concept.

Q12. Classify the following as strong acids, weak acids, strong bases, or weak bases: HCl, CH₃COOH, NaOH, NH₄OH, H₂SO₄, H₂CO₃.

Q13. (a) Compare the Arrhenius, Brønsted-Lowry, and Lewis concepts of acids and bases with one example for each.

(b) Identify the conjugate acid-base pairs in the following reactions:

(i) HCl + H₂O → H₃O⁺ + Cl⁻

(ii) NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

(iii) HCO₃⁻ + H₂O ⇌ H₂CO₃ + OH⁻

(c) A student claims that H₂O is neither an acid nor a base. Is the student correct? Explain using the Brønsted-Lowry concept.

Q14. (a) Define the following terms:

(i) Strong acid

(ii) Weak acid

(iii) Strong base

(iv) Weak base

(b) Explain why CH₃COOH is a weak acid while HCl is a strong acid, even though both produce H⁺ ions in water.

(c) Write the ionisation equations for HCl and CH₃COOH in water. How do they differ in terms of the degree of ionisation?

Q15. (a) Explain the concept of amphiprotic substances with suitable examples. How does water act as an amphiprotic solvent?

(b) Identify which of the following species can act as amphiprotic: H₂O, HCO₃⁻, HSO₄⁻, NH₃, OH⁻. For each amphiprotic species, write one reaction showing it as an acid and one showing it as a base.

(c) In the Indian context, explain why tamarind (imli) water tastes sour while soap solution feels slippery. Relate this to the nature of acids and bases.

Q16. Calculate the pH of the following solutions at 25°C:

(a) 0.01 M HCl

(b) 0.001 M NaOH

(c) A solution containing 0.05 M CH₃COOH (Ka = 1.8 × 10⁻⁵)

(d) A solution formed by mixing 50 mL of 0.1 M HCl with 50 mL of 0.1 M NaOH

Q17. The ionic product of water at 25°C is 1.0 × 10⁻¹⁴.

(a) Calculate the concentration of H⁺ and OH⁻ ions in pure water at 25°C.

(b) At 60°C, Kw = 9.6 × 10⁻¹⁴. Calculate the pH of pure water at this temperature. Is the water still neutral? Explain.

(c) A student claims that since the pH of water at 60°C is less than 7, the water has become acidic. Is the student correct? Justify your answer.

Q18. In India, many household products are either acidic or basic:

(a) Lemon juice has a pH of approximately 2.3. Calculate the H⁺ ion concentration. If you dilute 10 mL of lemon juice to 100 mL with water, what is the new pH? (Assume lemon juice behaves like a strong acid for this calculation.)

(b) Baking soda (NaHCO₃) solution has a pH of about 8.3. Calculate the OH⁻ ion concentration.

(c) A student mixes 20 mL of lemon juice (pH = 2.3) with 30 mL of baking soda solution (pH = 8.3). Assuming complete neutralisation, calculate the pH of the resulting mixture. (Treat lemon juice as containing H⁺ ions only and baking soda as containing OH⁻ ions only for simplicity.)

(d) Explain why antacids (which are basic) are used to relieve acidity in the stomach, using the concept of neutralisation.