DP Chemistry (first assessment 2025)
Question 19M.1A.SL.TZ1.26
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.1A.SL.TZ1.26 |
| Level | SL | Paper | 1A | Time zone | TZ1 |
| Command term | Question number | 26 | Adapted from | N/A |
26.
[Maximum mark: 1]
19M.1A.SL.TZ1.26
What is the mechanism of the reaction between alkenes and halogens in the absence of light?
A. radical substitution
B. electrophilic substitution
C. electrophilic addition
D. nucleophilic substitution
[1]
Markscheme
C
Examiners report
Only 33 % of candidates could identify the mechanism type with a large confusion between electrophilic addition and substitution.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.4—Electron-pair sharing reactions » Reactivity 3.4.5—Alkenes are susceptible to electrophilic attack because of the high electron density of the carbon–carbon double bond. These reactions lead to electrophilic addition. Deduce equations for the reactions of alkenes with water, halogens, and hydrogen halides.