DP Chemistry (first assessment 2025)
Question EXM.1A.HL.TZ0.9
| Date | May Example question | Marks available | [Maximum mark: 1] | Reference code | EXM.1A.HL.TZ0.9 |
| Level | HL | Paper | 1A | Time zone | TZ0 |
| Command term | Question number | 9 | Adapted from | N/A |
9.
[Maximum mark: 1]
EXM.1A.HL.TZ0.9
Which of the following statements is correct when a 1.0 M NH4+/NH3 buffer (pH = 9.2) is diluted to 0.5 M with water?
I. The ability of the buffer to resist changes in pH when acids are added will decrease.
II. The ability of the buffer to resist changes in pH when bases are added will decrease.
III. The pH of the buffer will be equal to 7.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
[1]
Markscheme
A
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.17—The pH of a buffer solution depends on both: • the pKa or pKb of its acid or base • the ratio of the concentration of acid or base to the concentration of the conjugate base or acid. Solve problems involving the composition and pH of a buffer solution, using the equilibrium constant.