The petri dish on the left has had some Fe3+(aq)
added to it, now we will add some SCN-(aq) to the
solution in the petri dish on the right.
When we add SCN-(aq) to the solution
in the petri dish on the right we observe the solution gets darker. This
is VERY interesting. Adding some SCN-(aq)
causes the solution to get darker, it appears that adding the SCN-(aq)
causes more FeSCN2+(aq) to be formed.
We can understand this to suggest that in the solution in the petri
dish on the right there must have been some Fe3+(aq).
So when I added SCN-(aq) there was a
reaction to produce more of the product, FeSCN2+(aq).
So the original beaker containing the solution of FeSCN2+(aq)
must also have some Fe3+(aq) present.
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