We performed a lab that involved the single displacement of copper(II)hydrate with aluminium.

Question

 One question asks; If you wanted to use aluminium as the limiting reagent, what changes in the procedure would be made? What visible evidence would you look for. The actual limiting reagent is copper.

Answer 1

Not sure what the Cu(II) hydrate is that you used.  It may have been CuCl2, or CuSO4, etc hydrate. Regardless, it won't matter for this question as long as it had a color, most likely blue.  Now, you have the following reaction

2Al(s) + 3Cu²⁺ ==> 2Al³⁺ + 3Cu(s)

Assuming the reaction starts out with a blue color, if Cu²⁺ is limiting, the solution should be colorless at the end of the experiment, suggesting no more Cu2+(blue) is present, and it has all been displaced and reduced to Cu(s) which is colorless.

To make Al the limiting reactant, you can change the amount of Al added to the reaction. Instead of using a molar ratio of 2 Al to 3 Cu²⁺, use a molar ratio less than that.  This will make Al limiting, and the visible evidence would be that at the end of the experiment, the solution still had a blue color.