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Distinguish Between Alkanes And Alkenes
The article focuses on a test that may distinguish between an alkane and alkene; it is the official test for an alkene
Date : 04/03/2023
Author Information
Uploaded by : Jonathan
Uploaded on : 04/03/2023
Subject : Chemistry
One of the most common tests in organic chemistry in Year 11 and in particular at Year12 is to tell the difference between an alkane and alkene. In a test-tube containing about 1cm3 of bromine water (red-brown in colour), a few drops of the liquid hydrocarbon (e.g. hexane and hex-1-ene) is added and a stopper added and shaken. After a few seconds, the bromine-water containing the alkene decolourises (i.e. red-brown to colourless), whereas for the alkane (saturated hydrocarbon) there is no colour change.
What`s going on?
Only the C=C double bond in the alkene can react with aqueous bromine to form an addition compound (halogenoalkane), such as gaseous ethene being bubbled into bromine-water:
CH2=CH2 + ; Br2(aq) ->; CH2Br-CH2Br
Do not confuse this with free-radical substitution (chlorine in direct sunlight/UV): both compounds with react with chlorine rapidly under these conditions to give complex mixtures!
This resource was uploaded by: Jonathan