Buffer Solutions - UNSOLVED PRACTICE SET

Q7. Define a buffer solution. Name the two types of buffer solutions with one example each.

Q8. Explain the mechanism by which an acidic buffer (CH₃COOH/CH₃COONa) resists pH change when a small amount of NaOH is added.

Q9. Calculate the pH of a buffer solution containing 0.1 M CH₃COOH and 0.1 M CH₃COONa. (pKa of CH₃COOH = 4.74)

Q10. Why can't a mixture of HCl and NaCl act as a buffer solution? Explain with reasoning.

Q11. Explain why the buffer capacity is maximum when the ratio [salt]/[acid] = 1. What is the significance of this condition?

Q12. A student prepares a buffer by mixing 100 mL of 0.1 M NH₄OH with 100 mL of 0.1 M NH₄Cl. Is this a buffer solution? If yes, what type? Explain.

Q13. (a) Define buffer solution and buffer capacity. Explain the two types of buffer solutions with examples.

(b) Derive the Henderson-Hasselbalch equation for an acidic buffer.

(c) A buffer solution contains 0.2 M CH₃COOH and 0.1 M CH₃COONa. Calculate its pH. (pKa = 4.74)

Q14. (a) Explain the mechanism of action of a basic buffer (NH₄OH/NH₄Cl) when:

(i) A small amount of HCl is added

(ii) A small amount of NaOH is added

(b) Calculate the pH of a buffer containing 0.15 M NH₄OH and 0.25 M NH₄Cl. (Kb for NH₄OH = 1.8 × 10⁻⁵)

(c) What happens to the pH of this buffer if it is diluted 10 times? Explain.

Q15. (a) Explain the biological importance of buffer systems with special reference to the bicarbonate buffer system in human blood.

(b) The pH of blood is maintained at 7.4 by the H₂CO₃/HCO₃⁻ buffer system. If the ratio [HCO₃⁻]/[H₂CO₃] is 20:1, calculate the pKa of carbonic acid.

(c) During strenuous exercise, lactic acid is produced in muscles. Explain how the blood buffer system prevents a drastic drop in blood pH.

Q16. Calculate the pH of the following buffer solutions:

(a) 0.1 M CH₃COOH and 0.1 M CH₃COONa (pKa = 4.74)

(b) 0.05 M CH₃COOH and 0.15 M CH₃COONa (pKa = 4.74)

(c) 0.2 M NH₄OH and 0.1 M NH₄Cl (pKb = 4.74)

(d) 0.1 M HCN and 0.2 M NaCN (pKa = 9.31)

For each case, also calculate the pH change when 0.01 mol of HCl is added to 1 L of the buffer.

Q17. A buffer solution is prepared by mixing 50 mL of 0.2 M CH₃COOH with 50 mL of 0.2 M CH₃COONa.

(a) Calculate the pH of this buffer. (pKa = 4.74)

(b) Calculate the new pH after adding 5 mL of 0.1 M HCl to this buffer.

(c) Calculate the new pH after adding 5 mL of 0.1 M NaOH to the original buffer.

(d) Compare the pH changes in parts (b) and (c) with what would happen if the same amounts of HCl and NaOH were added to 100 mL of pure water. Comment on the buffer action.

Q18. In India, many traditional food preservation methods rely on maintaining pH:

(a) Pickles are preserved in vinegar (acetic acid) with added salt. Explain how this creates a buffer-like environment that inhibits bacterial growth.

(b) A food scientist wants to prepare a buffer to maintain pH 4.5 for a new sauce recipe. Calculate the ratio of [CH₃COONa]/[CH₃COOH] needed. (pKa of CH₃COOH = 4.74)

(c) If the scientist uses 0.5 M CH₃COOH, what concentration of CH₃COONa is required?

(d) In the human body, the phosphate buffer system (H₂PO₄⁻/HPO₄²⁻) helps maintain intracellular pH. If the pH of a cell is 7.2 and the pKa₂ of phosphoric acid is 7.21, calculate the ratio [HPO₄²⁻]/[H₂PO₄⁻]. Explain the significance of this ratio in cellular metabolism.