DP Chemistry (first assessment 2025)
Question 22M.2.SL.TZ1.a(iii)
| Date | May 2022 | Marks available | [Maximum mark: 3] | Reference code | 22M.2.SL.TZ1.a(iii) |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | a(iii) | Adapted from | N/A |
a(iii).
[Maximum mark: 3]
22M.2.SL.TZ1.a(iii)
Explain the relative lengths of the three bonds between N and O in nitric acid.
[3]
Markscheme
Any three of:
two N-O same length/order ✔
delocalization/resonance ✔
N-OH longer «than N-O»
OR
N-OH bond order 1 AND N-O bond order 1½ ✔
Award [2 max] if bond strength, rather than bond length discussed.
Accept N-O between single and double bond AND N-OH single bond.
Examiners report
Poorly done; some explained relative bond strengths between N and O in HNO3, not relative lengths; others included generic answers such as triple bond is shortest, double bond is longer, single longest.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.4—Electron-pair sharing reactions » Reactivity 3.4.2—In a nucleophilic substitution reaction, a nucleophile donates an electron pair to form a new bond, as another bond breaks producing a leaving group. Deduce equations with descriptions and explanations of the movement of electron pairs in nucleophilic substitution reactions.