Buffer Capacity - AP Chemistry

1. What is the role of buffers in biological systems?

   Buffers maintain stable pH for biological processes. Essential for enzyme function, cellular processes, and metabolic reactions.

2. What is a buffer's response to added acid or base?

   A buffer resists pH changes. Weak acid neutralizes added base; conjugate base neutralizes added acid.

3. Find the buffer capacity: 0.1 mol base changes pH by 0.2.

   Buffer capacity = 0.1/0.2 = 0.5. Standard application of the buffer capacity formula.

4. What is the buffer capacity if 0.05 mol of NaOH causes a pH change of 0.1?

   Buffer capacity = 0.05/0.1 = 0.5. Applying the definition: capacity = moles added divided by pH change.

5. What is the definition of buffer capacity?

   Buffer capacity is the ability of a buffer to resist changes in pH. Quantifies how well buffers maintain stable pH when acids or bases are added.

6. Identify the formula for calculating buffer capacity.

   Buffer capacity = Δn/ΔpH. Where $\Delta n$ is moles added and $\Delta pH$ is the resulting pH change.

7. What determines the effective pH range of a buffer?

   The pKa of the acid and the concentration ratio. Buffer works best within $\text{p}K_a \pm 1$ pH unit range.

8. How does the ratio of buffer components affect buffer capacity?

   A 1:1 ratio of acid to conjugate base maximizes buffer capacity. Equal amounts provide optimal resistance to pH changes in both directions.

9. How is buffer capacity related to the Henderson-Hasselbalch equation?

   It helps determine the pH range where buffer capacity is effective. Shows optimal buffering occurs when pH = $\text{p}K_a$ and ratio is 1:1.

10. Choose the correct statement about strong acids and buffers.

    Strong acids can overwhelm buffers, reducing capacity. Adding excess strong acid depletes the conjugate base component.

11. Identify a situation where buffer capacity is crucial.

    In biochemical reactions requiring specific pH. Enzyme catalysis, protein folding, and cellular metabolism require stable pH.

12. How is buffer capacity measured experimentally?

    By titration with a strong acid or base. Gradual addition while monitoring pH change determines buffering ability.

13. How does the presence of a buffer affect a titration curve?

    It flattens the curve within the buffer range. Creates a flat region where pH changes slowly with added titrant.

14. What is the role of a buffer in a solution?

    A buffer maintains a stable pH in a solution. Neutralizes added acids or bases to prevent large pH changes.

15. Calculate buffer capacity: 0.05 mol acid causes pH change of 0.25.

    Buffer capacity = 0.05/0.25 = 0.2. Direct calculation using capacity = moles added / pH change.

16. Calculate the buffer capacity: 0.02 mol base changes pH by 0.04.

    Buffer capacity = 0.02/0.04 = 0.5. Standard buffer capacity calculation using the defining formula.

17. What happens to buffer capacity when the pH is far from pKa?

    Buffer capacity decreases. Maximum capacity occurs when pH equals $\text{p}K_a$ of the buffer system.

18. Identify the primary buffer system in human blood.

    The bicarbonate buffer system. $\text{HCO}_3^- / \text{H}_2\text{CO}_3$ system maintains blood pH around 7.4.

19. Identify the primary function of a buffer in a titration.

    To stabilize pH changes near the equivalence point. Buffers prevent sharp pH changes during acid-base neutralization reactions.

20. What is the optimal pH range for a buffer with pKa of 4.75?

    Optimal pH range: 3.75 to 5.75. Effective buffering range is $\text{p}K_a \pm 1$ pH unit.

21. Which factors affect buffer capacity?

    Concentration of buffer components and their ratio. Higher concentrations and equal ratios provide maximum buffering effectiveness.

22. What is the significance of the pKa value in buffers?

    pKa indicates the pH at which a buffer is most effective. Buffer capacity is maximized when solution pH equals the acid's $\text{p}K_a$.

23. How does temperature affect buffer capacity?

    Temperature can affect dissociation and thus buffer capacity. Higher temperatures increase ionization, affecting buffer equilibrium.

24. What is the typical composition of a buffer solution?

    A weak acid and its conjugate base or vice versa. Weak acid/conjugate base pairs resist pH changes when acids or bases are added.

25. What is the effect of increasing buffer concentration on buffer capacity?

    Increasing concentration increases buffer capacity. More buffer molecules available to neutralize added acids or bases.

26. Find the pH change if 0.01 mol of HCl is added to a buffer with capacity 0.2.

    ΔpH = 0.01/0.2 = 0.05. Using buffer capacity formula: $\Delta pH = \Delta n \div \text{capacity}$.

27. Calculate buffer capacity: 0.02 mol of acid changes pH by 0.1.

    Buffer capacity = 0.02/0.1 = 0.2. Direct application of capacity formula: $\Delta n / \Delta pH$.

28. What is the relationship between buffer capacity and buffer range?

    Buffer capacity is highest within the buffer range. Buffer range ($\text{p}K_a \pm 1$) defines where capacity is most effective.

29. What is the result of adding a strong base to an acidic buffer?

    The buffer neutralizes the base, maintaining pH. Weak acid component neutralizes the added base to minimize pH change.

30. Calculate pH change: 0.01 mol NaOH in buffer capacity of 0.5.

    ΔpH = 0.01/0.5 = 0.02. Using the buffer capacity equation to find resulting pH change.

31. What is the effect of a strong acid on a weak acid buffer?

    It can decrease the buffer's capacity rapidly. Strong acid consumes conjugate base, reducing the buffer's effectiveness.

32. Why is a 1:1 ratio of acid to conjugate base optimal for buffering?

    It maximizes buffer capacity by keeping pH near pKa. When concentrations are equal, pH equals $\text{p}K_a$ for maximum effectiveness.

33. How does dilution affect buffer capacity?

    Dilution decreases buffer capacity. Lower concentrations mean fewer buffer molecules to resist pH changes.

34. How does pH affect enzyme activity in buffered solutions?

    Buffers maintain optimal pH for enzyme activity. Enzymes require specific pH ranges for proper folding and catalytic activity.

35. What happens to buffer capacity with equal concentrations of acid and base?

    Buffer capacity is maximized. Equal concentrations create optimal conditions for resisting pH changes.

36. Identify a common laboratory buffer system.

    The phosphate buffer system. $\text{HPO}_4^{2-} / \text{H}_2\text{PO}_4^-$ system with $\text{p}K_a$ of 7.2.

37. What does Δn represent in the buffer capacity formula?

    Δn is the amount of acid or base added. Moles of strong acid or base added to the buffer solution.

38. How does buffer capacity change with pH deviation from pKa?

    It decreases as pH moves away from pKa. Maximum effectiveness occurs at pH = $\text{p}K_a$, declining as pH deviates.

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