DP Chemistry (first assessment 2025)
Question 19M.2.SL.TZ2.d(ii)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ2.d(ii) |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Predict | Question number | d(ii) | Adapted from | N/A |
d(ii).
[Maximum mark: 2]
19M.2.SL.TZ2.d(ii)
Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)
[2]
Markscheme
«additional HCO3-» shifts position of equilibrium to left [✔]
pH increases [✔]
Note: Do not award M2 without any justification in terms of equilibrium shift in M1.
Examiners report
A significant number of candidates omitted the “equilibrium” involved in the dissolution of a weak base.
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–].
Reactivity 2. How much, how fast and how far? » Reactivity 2.3—How far? The extent of chemical change » Reactivity 2.3.4—Le Châtelier’s principle enables the prediction of the qualitative effects of changes in concentration, temperature and pressure to a system at equilibrium. Apply Le Ch.telier’s principle to predict and explain responses to changes of systems at equilibrium.