DP Chemistry (first assessment 2025)
Question 21N.2.SL.TZ0.7b
| Date | November 2021 | Marks available | [Maximum mark: 3] | Reference code | 21N.2.SL.TZ0.7b |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Formulate | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 3]
21N.2.SL.TZ0.7b
(b)
Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.
[3]
Markscheme
Cl· + C2H6 → ·C2H5 + HCl ✔
·C2H5 + Cl2 → Cl· + C2H5Cl ✔
·C2H5 + Cl· → C2H5Cl
OR
Cl· + Cl· → Cl2
OR
·C2H5 + ·C2H5 → C4H10 ✔
Do not penalize incorrectly placed radical sign, eg C2H5·.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.3—Electron sharing reactions » Reactivity 3.3.3—Radicals take part in substitution reactions with alkanes, producing a mixture of products. Explain, using equations, the propagation and termination steps in the reactions between alkanes and halogens.