Bromine test for saturation help! (1 Viewer)

[tuliptea]

heyy
just wondering,

- is bromine water more likely to dissolve more easily in water or a hydrocarbon, and why?
(is it water because of non-polarity?)
- and for this experiment (bromine water test for saturation), what must be done to control the validity & to allow the use of qualitative observation of results?

(i hate validity) hehe
thanks!

 

[NCAChris]

I think you've misunderstood this practical

So firstly Bromine water is added to two unknown solutions of hydrocarbons in order to determine whether the hydrocarbon is saturated or unsaturated (i.e whether its an alkene or alkane)
Depending on the conditions; When added to an unsaturated hydrocarbon/alkene the bromine water will rapidly decolourise and turn from brown to clear as the bromine is removed from the solution to saturate the alkene. This is known as an addition reaction as the double bond in the hydrocarbon is broken and replaced by the bromine.
When the bromine is added to the saturated hydrocarbon, there will either be no reaction or a very slow reaction depending on whether there is UV or not. When revealed to sunlight the UV will break the C-H single bonds and allow the bromine to substitute the hydrogens in whats known as a substitution reaction. However if you do this in a dark room, there will be no reaction at all and the solution will remain brown.

Validity: Most important factor of remaining valid is to just make sure you do this practical in a dark room, to prevent the saturated hydrocarbon from reacting with the bromine water. However the reaction is so much slower that in reality if you just observe it you could easily tell the difference. But to satisfy the markers just talk about the dark room

 

[MzG1zi]

for validity you can also have a control (or two) by placing a test tube of each alkane and alkene (without the bromine water) in the same environment as the hydrocarbon+bromine water test tubes, showing that the colour change with the alkene is purely a result of the addition of bromine and not any other substances.