9.15C - Distinguishing alkanes and alkenes
Use bromine water to distinguish an alkane from an alkene, then explain the observations using their bonds. You will also learn why a colour change must be recorded precisely. This is a separate Chemistry point.
Carrying out and reading the test
Bromine water is an orange aqueous solution of bromine. To compare an alkane and an alkene, add a few drops to small separate samples and shake gently. Work at room temperature away from strong sunlight or UV light. Wear eye protection, avoid skin contact and follow the teacher’s ventilation instructions: bromine water is irritating and its vapour is hazardous.
| Sample | Observation after shaking with orange bromine water |
|---|---|
| alkane | orange colour remains |
| alkene | orange colour disappears; mixture becomes colourless |
Orange-brown is also a valid starting-colour description. Colourless means there is no colour; “clear” means transparent and can describe an orange solution as well. Record the starting and final colours.
Use this test when the possible samples are alkanes and alkenes. A positive result does not identify a particular alkene: many alkenes decolourise bromine water. Do not extend the conclusion to every unknown chemical from this test alone.
Continue this lesson.
You’re previewing NovaLearn without an account. Create a free account to read the rest.
Create free account