DP Chemistry (first assessment 2025)
Question 19M.1A.SL.TZ1.19
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.1A.SL.TZ1.19 |
| Level | SL | Paper | 1A | Time zone | TZ1 |
| Command term | Question number | 19 | Adapted from | N/A |
19.
[Maximum mark: 1]
19M.1A.SL.TZ1.19
Which solution is basic at 25 °C?
Kw = 1.0 × 10−14
A. [H+] = 1.0 × 10−3 mol dm−3
B. [OH−] = 1.0 × 10−13 mol dm−3
C. solution of pH = 4.00
D. [H3O+] = 1.0 × 10−13 mol dm−3
[1]
Markscheme
D
Examiners report
This was very poorly answered and had one of the highest discriminatory indices. More candidates thought that a basic solution would have [OH- ] = 1.0 x 10-13 mol dm-3 , rather than [H3O+ ] = 1.0 x 10-13 mol dm-3
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–].