Video Transcript
In a laboratory demonstration of
the electrolysis of zinc iodide, a teacher melts the compound before turning on the
electricity. What is the reason for this step in
the procedure? (A) Melting the salt ensures a good
rate of reaction. (B) This step ensures good
connections between the substance and the electrodes. (C) The reaction is exothermic. (D) The zinc and iodide ions must
be free to move. Or (E) this step removes water
molecules adhering to the zinc iodide powder.
Electrolysis is a chemical process
where electricity is passed through an electrolyte, causing it to decompose into its
constituent elements. A simple electrolytic cell can be
set up using two electrodes and a DC power supply which drives an electric current
through the electrodes which are placed into a substance known as the
electrolyte.
For the reaction to proceed long
enough to produce our products, we need a continuous flow of electrons to move
around the circuit. And the electrolyte is a substance,
or mixture, that contains mobile ions that can undergo electrolysis by allowing a
current to flow. We need the ions in the electrolyte
to be able to move in order for this to happen.
In the example in the question, the
substance we are examining is zinc iodide. We are not told that we are
dissolving the zinc iodide in water. In fact, the teacher melts the zinc
iodide, so what we have here is a molten solution. In the molten state, the ions are
mobile so the current can be carried between the two electrodes. This would be impossible if the
zinc iodide were in a solid state.
If we examine our answer choices,
we can see that the correct answer choice is (D). The zinc and iodide ions must be
free to move.
