What chemical test can be used to differentiate between alkenes and alkanes. Describe and explain the results.

Alkenes decolourise bromine water (orange/brown to colourless) while alkanes cause no change in colour. An electrophilic addition reaction occurs with the alkene. In a reaction between ethene and bromine water, Br2 is shown as an electrophile, attracted to electrons due to the formation of a partial positive charge, which attacks the exposed pi bond in ethene. The two electrons in one of the ethene double bonds then goes to the partially positively charged Br atom, causing the carbon atoms to become positively charged. As both Br atoms have two spare electrons, they form bonds with either positively charged carbon atom. Therefore the decolourisation occurs because both bromine atoms have become ionised in the reaction. This addition reaction cannot occur in alkanes because of the lack of carbon - carbon double bonds.

SE
Answered by Sito E. Chemistry tutor

12301 Views

See similar Chemistry A Level tutors

Related Chemistry A Level answers

All answers ▸

What is meant by the term optical isomerism?


Can you help me with the question: "State and explain the trend in boiling temperature of hydrogen halides down the group"?


What is an empirical formula and how do I calculate it?


Figure 1 shows a maxwell-Boltzmann distribution of molecular energies of a sample of gas at a fixed temperature. (a) Label the y axis. (b) On Figure 1, sketch a maxwell-Boltzmann distribution for the same sample of gas at a lower temperature.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences