DP Chemistry (first assessment 2025)
Question 22M.1A.SL.TZ2.24
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.1A.SL.TZ2.24 |
| Level | SL | Paper | 1A | Time zone | TZ2 |
| Command term | Apply | Question number | 24 | Adapted from | N/A |
24.
[Maximum mark: 1]
22M.1A.SL.TZ2.24
What happens to the amount of hydroxide ions and hydroxide ion concentration when water is added to a solution of NH3 (aq)?
[1]
Markscheme
C
Examiners report
35% of the candidates deduced the change in amount of OH- and [OH-] when water is added to NH3(aq). The majority of candidates recognized the increase in the amount of OH- due to the shift in the equilibrium position but assumed that the concentration of OH- increased as well ignoring the effect of the dilution. Some teachers commented that this question was too complicated.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.1—Proton transfer reactions » Reactivity 3.1.5—The ion product constant of water, Kw, shows an inverse relationship between [H+] and [OH–]. Kw = [H+] [OH–]. Recognize solutions as acidic, neutral and basic from the relative values of [H+] and [OH–].