Understanding the setup of a chemistry lab about redox
I'm wondering why is it not necessary to mix a metal like Fe into its own solution $\ce{Fe(NO3)2}$ (like you would do when setting up an electrochemical cell)?


First remember what the purpose of your experiment was:


  To determine the relative activity of several metals we observed reactions between the metals and aqueous solutions of dissolved metals.


In an electrochemical cell setup, $\ce{Fe}$ would be in two-way equilibrium with $\ce{Fe^2+}$:

$$\ce{Fe + Fe^2+ &lt;=&gt; Fe + Fe^2+}$$

When power was drawn from the cell you then get:

$$\ce{Fe -&gt; 2 e- + Fe^2+}$$

Where as with another salt such as copper which is less reactive, the copper will oxidize the iron in one direction with no reverse reaction.

$$\ce{Fe + Cu^2+ -&gt; Cu + Fe^2+}$$

or with zinc which is more reactive no reaction will occur at all:

$$\require{cancel} \ce{Fe + Zn^2+ \cancel{\ce{&lt;=&gt;}} Zn + Fe^2+ -&gt;Fe + Zn^2+}$$