[Kelsi Jade]

Ok, I'm still trying to figure out some questions regarding an electrochemical cell for and orange juice clock involving a magnesium strip and a copper strip in 400ml of orange juice with wireing connecting them to a clock.

So far I have determined that the Mg is what is being oxidized (and is hence the anode) 1)but I'm a little stuck on what is being reduced - I know it can't be the copper because there are no copper ions in the OJ so what else? Water maybe?

1/2 reactions:
oxidized:  Mg(s) -> Mg²⁺(aq) + 2e-   whereE⁰=2.37V (vs. SHE)
reduced:  2H⁺(aq) + 2e- -> H₂(g) ?where E⁰=0V (vs. SHE)
overall:  Mg(s) + 2H⁺(aq) -> Mg²⁺(aq) +H₂(g)   ?


If so, the E⁰_cell would be
E⁰_cell=E⁰_{(reduced 1/2 cell)} - E⁰_{(oxidized 1/2 cell)}= (0V)-(2.37)V
E⁰_cell=2.37V

2. The pH of the orange juice was measured to be 1.5. What is the measurement electrochemical potential of the organic juice clock electrochemical cell?

3.The clock requires a minimum voltage of 1.5 volts for it to function. Now, if we replace the magnesium electrode with a lead electrode, will the clock still run? How about replacing the electrode with a stainless steel plate?

4.Would the system work if we put Cu2+ ions into the orange juice solution?

5. What would happen if we titrate the acid solution with a strong base while the clock is running?

6.What happens to the voltage if we put Mg2+ into the system?

7.Are the complex ions of Mg2+ with citric acid important to the potential value?

8.What is the relationship between the clock ticking and different juices? Why is this relationship so?

9.At the end of the experiment, would you expect the voltage of orange juice electrochemical cell decrease or increase?

If you can help with any of these questions it would be greatly appreciated!!!!!!

[Kelsi Jade]

OK, I think I figured out the first 5 questions. For #6 when you add the Mg2+ ions to the solution, that would decrease the voltage because there would be an excess of Magnesium, and not enough H+ ions to compensate?

[Arkcon]

8.What is the relationship between the clock ticking and different juices? Why is this relationship so?

Now this one is a tough one, it would really depend on the clock, in some ways.  As I understand a typical digital clock, it's driven by the oscillations of a quartz crystal, driven by the charge potential.  So, as long as there is enough volts across the metal can it's contained in, it should oscillate at the same rate, driven only by it's dimensions and structure.  But that's solid state physical chemistry, not electrochemistry.  Did you see the clock speed up or slow down in different solutions?  Has anyone ever seen a digital clock "lose" time like a sweep-hand mechanical clock?

[Kelsi Jade]

Would it make a difference if the clock were not digital? I know the clock in the experiment set-up was analog.