Chemistry Homework

Question

I've done most of my homework, but there were a few problems. Please answer these questions with an explanation, I don't just want an answer.

4) Why do electrolytic cells require an outside source of electrical power to drive the reaction? Can you give me an example of an electrolytic cell application from real life?

7) What would happen if an aluminum wire were dipped into a solution of tin (II) sulfate? Note: The answer should have something to do with the chart of standard electrode potentials.

8) Why are some standard reduction potentials negative and others positive?

 

Homework is due tomorrow.

Answer 1

4) Electrolytic cells (unlike galvanic/voltaic cells) are NOT spontaneous, and thus they require an external source of electricity.  This essentially drives the reaction.  Without this, the reaction would not occur as ∆G would be positive (non spontaneous reaction).  An example would be the electrolysis of water, where an electric current flows into water and it causes water molecules to come apart and form H₂ (hydrogen gas) and O₂ (oxygen gas).  This is actually used commercially for these purposes.

7)  Standard reduction potential for tin is -0.14 V for Sn²⁺ + 2e^- ===> Sn(s)

For Aluminum it is Al³⁺ + 3e^- ===> -1.66 V

Thus, Al can replace tin in a single replacement reaction, as Sn²⁺ will be reduced and Al(s) will be oxidized. The overall reaction would be 2Al(s) + 3Sn²⁺(aq) ===>2Al³⁺(aq) + 3Sn(s).  In words, what would happen is that the Al would appear to dissolve and turn into aluminum sulfate, while the tin would come out of solution as solid tin.

 

8)  All STANDARD reduction potentials are relative to that for HYDROGEN, which receives a value of zero for 2H⁺ + 2e^- ==> H2(g), so some will be positive and some will be negative.