bromine water (1 Viewer)

[onebytwo]

earlier in the year we used bromine solution to illustrate the difference in reactivites between alkanes and alkenes.
i was just wandering, how can bromine go into solution, if it is a non-polar molecule, i.e. even electron distribution between the two covalently held bromine atoms? at most the only intermolecular forces that should exist are the weak dispersion forces between H2O and Br2 since there are unlike forces i.e. h-bonds between water molecules and dispersion forces between Br2 molecules.
can someone please explain why Br2 dissolves in H20.......
thanks

 

[pkc]

Bromine is only slightly soluble in water remember - as are all diatomic elements such as H2,O2, I2 etc.

Whilst diatomic molecules do not have a permanent dipole as you say, they do have instantaneous and induced dipoles which are only weak, but enough to allow limited solubility in polar water.

Induced dipoles These occur when one molecule with a permanent dipole repels another molecule's electrons, "inducing" a dipole moment in that molecule

Instantaneous dipoles: These occur due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole.

http://www.elmhurst.edu/~chm/vchembook/173solubleononp.html
http://en.wikipedia.org/wiki/Dipole

Hope this helps.

 

[onebytwo]

thanks, that clears that up

 

[Farmerism]

hey i thought bromine was an element that was liquid at toom temperature anyway.

like mercury

could you also use just Br2 to test for alkenes or is it just HBr

 

[punk_tartan]

hey i thought bromine was an element that was liquid at toom temperature anyway.

like mercury

could you also use just Br2 to test for alkenes or is it just HBr

the chemical used to determine between alkanes and alkenes is Br2 and i THINK its in the elemetal form in soloutiuon.... someone please correct me if im wrong !!

 

[pkc]

Br2 is the brown substance which changes colour in the bromine water test for alkenes. (HBr is a very pale yellow colour and does no indication).

Pure Br2 is a liquid at room temperature and is very aggessive, hence it is used in solution in a lab.

Hope this helps.

 

[funking_you]

the chemical used to determine between alkanes and alkenes is Br2 and i THINK its in the elemetal form in soloutiuon.... someone please correct me if im wrong !!

If you react an alkene, e.g. ethene with liquid bromine, Br₂(l), only one product is formed, i.e. 1,2-dibromoethane.

however, 'bromine water' is usually a 3-5% solution of liquid bromine.
The presence of the water complicates the reaction and it turns out that there are more than one product formed. The major product of ethene and 'bromine water' is actually 2-bromoethanol, with only a small amount of 1,2-dibromoethane formed.

This is because the liquid bromine that dissolve in the water will reaction with the water: Br2(l) + H2O <---> BrOH(aq) + HBr(aq).

HOWEVER FOR HSC PURPOSES, discussing this more advanced mechanism for the reaction is NOT required.
It is sufficient to just say that ethene reacts with 'bromine water' to from 1,2-dibromoethane.
Why? because the aim of this reaction (in the hsc syllabus) is to observe the decolourisation of bromine water, identifying that a reaction took place.