Whose the … daddy?

One year old today!

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Last time I asked if you could identify the halogen / halide displacement reactions taking place in the .gif animation.

Halogen / halide ion reactions in water

Halogen / halide ion reactions in water

It makes sense that no change is observed when chlorine water is added to sodium chloride, bromine water is added to sodium bromide and aqueous iodine is added to potassium iodide. In all three cases the products of any displacement reactions would be the same as the reactants.
chlorine + sodium chloride -> chlorine + sodium chloride
bromine + sodium bromide -> bromine + sodium bromide
iodine + potassium iodide -> iodine + potassium iodide

Controls crossed out in red

Controls crossed out in red

For the remaining six combinations only three produce definitive changes in colour or a change in intensity of colour that can be attributed to a displacement reaction taking place.

Identifying the displacement reactions

Identifying the displacement reactions

The reactions are:
1. chlorine + sodium bromide -> bromine + sodium chloride
The reaction mixture turns very pale yellow due to the formation of bromine (which is orange or dark brown depending on the concentration).
2. chlorine + potassium iodide -> iodine + potassium chloride
The reaction mixture turns orange due to the production of iodine. Again, iodine solutions can be much darker orange to brown, depending on the concentration of iodine present.
3. bromine + potassium iodide -> iodine + potassium bromide
The reaction mixture is much darker orange than the control reaction (to the left of it, in the middle of the middle row) because iodine produces a much darker orange/brown colour than bromine at the same concentration.
Thus, the displacement reactions follow the trend in reactivity for Group 7; any halogen will displace halide ions from solution of members below it in the group.
Or put simply:
Chlorine displaces bromide ions and iodide ions
and bromine displaces iodide ions from solution.
So, whose the daddy? Well, fluorine is the most reactive element in Group 7, but its so darn reactive that it is too dangerous to use in the school laboratory. One would be unable to use it in these kind of displacement reactions because fluorine gas would react with water.
Why is fluorine so reactive? And what happened when hydrogen met fluorine?

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One thought on “Whose the … daddy?

  1. That should have read:
    “1 chlorine + sodium bromide -> bromine + sodium chloride
    The reaction turns very pale yellow due to the formation of bromine (which can be orange or dark brown depending on the concentration)”
    Nigel

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