DP Chemistry (first assessment 2025)
Question 19M.2.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ1.b |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
19M.2.HL.TZ1.b
Enantiomers can be identified using a polarimeter. Outline how this instrument differentiates the enantiomers.
[2]
Markscheme
«plane-»polarized light passed through sample [✔]
analyser/second polarizer determines angle of rotation of plane of plane-polarized light
OR
each enantiomer rotates plane «of plane-polarized light» in opposite directions «by the same angle» [✔]
Examiners report
Very poorly answered. Few scored any marks at all when outlining how a polarimeter can be used to differentiate between enantiomers. Many referred to the light or the enantiomers themselves being rotated.
Syllabus sections
Structure 3. Classification of matter » Structure 3.2—Functional groups: Classification of organic compounds » Structure 3.2.7—Stereoisomers have the same constitution (atom identities, connectivities and bond multiplicities) but different spatial arrangements of atoms. Describe and explain the features that give rise to cis-trans isomerism; recognize it in non-cyclic alkenes and C3 and C4 cycloalkanes. Draw stereochemical formulas showing the tetrahedral arrangement around a chiral carbon. Describe and explain a chiral carbon atom giving rise to stereoisomers with different optical properties. Recognize a pair of enantiomers as non-superimposable mirror images from 3D modelling (real or virtual).