Science Buddies: "Ask an Expert"

We are doing the project "Water to Fuel to Water: The Fuel Cycle of the Future" and have few questions that are not clear after going through the details.
1. Why is "Phosphate buffer solution" used to conduct the experiment and why not water (since the project is all about using water splitting to create fuels)?
2. What does 0.1M mean in "0.1M Phosphate buffer solution"?
3. How much cobalt nitrate should be put in the jar each time? It is not very clear from the instructions.

Hello and welcome to the forums.

I will try and help with your questions, although I am not a chemist and I've never done this experiment.

1. You are splitting water in this experiment. The reaction speeds up in the presence of the catalyst. The catalyst is

formed from cobalt ions (Co) in a phosphate (Pi) buffered solution (Co-Pi).

You need both the Phosphate and Cobalt to create the catalyst and make this experiment work. To control as many variables as possible, you are comparing the results after the addition of Cobalt to when there is no Cobalt in the system. This means you start with the Phosphate buffered solution in the water, and use this solution as the control.
2. 0.1M means 0.1 Molar. See here http://en.wikipedia.org/wiki/Molar_concentration for a definition of molarity.
3. I can't say exactly how many grams to add each time, but it looks like just a few grains.

Keith

Please help on the following questions:

1. Why are we using Nickel metal strips as electrodes and not any other metal?

2. The voltage readout on each of my "9V" battery is between 10.11 and 10.15V. When I connect all 4 9V batteries in series, the total voltage readout is 40.3V. Is this okay?

3. How do I know that how much voltage is dropped across the 10,000 Ohm resistor and electrochemical cell in my experiment? Technical note1 in procedure indicates approx 30v across the 10,000 Ohm resistor and 1.5-3v are dropped across the electrochemical cell. How did they come up with these values?

4. Why does the procedure assume a value of 1.23V for the ideal voltage? How is this value calculated?

5. How is Hydrogen strored that is created as part of the water splitting reaction?

6. When I added Cobalt Nitrate in the last before the voltage stabilzed, the voltage reading on the voltmeter was 1.94v but the voltage reading in the clear Phosphate Buffer solution after that was 2.02V. Why the voltage reading increased after putting the electrodes in clear Phosphate Buffer solution?

AjayJain73 wrote:Please help on the following questions:
1. Why are we using Nickel metal strips as electrodes and not any other metal?

This is a very interesting area of background research. The electrodes work best when they have certain electrochemical properties relative to the metal being plated on them. One interesting source of information on this that I found by searching for "nickel electrodes electrolysis" is at: https://sites.google.com/site/urbangeek ... electrodes

AjayJain73 wrote: 2. The voltage readout on each of my "9V" battery is between 10.11 and 10.15V. When I connect all 4 9V batteries in series, the total voltage readout is 40.3V. Is this okay?

Yes, that should be fine. 9V is a "nominal" voltage. A well charged battery is usually a bit above the voltage it's labelled as.

AjayJain73 wrote: 3. How do I know that how much voltage is dropped across the 10,000 Ohm resistor and electrochemical cell in my experiment? Technical note1 in procedure indicates approx 30v across the 10,000 Ohm resistor and 1.5-3v are dropped across the electrochemical cell. How did they come up with these values?

I can't really improve on the explanation given in the wikipedia article on this topic: http://en.wikipedia.org/wiki/Voltage_drop

AjayJain73 wrote: 4. Why does the procedure assume a value of 1.23V for the ideal voltage? How is this value calculated?

Basically, that's the voltage necessary to cause the chemical reaction to occur where water splits into hydrogen and oxygen. The reason for this particular voltage isn't easy to explain. There's a beginning of an explanation here: http://en.wikipedia.org/wiki/Electrolys ... he_process, but really that's a bit more of an advanced topic than most people would expect from a 6-8 grader.

AjayJain73 wrote: 5. How is Hydrogen strored that is created as part of the water splitting reaction?

In the case of this experiment, the hydrogen is not stored, and I wouldn't necessarily recommend trying to store it. Hydrogen is pretty volatile stuff, and can accumulate to explosive concentrations reasonably easily. In a real electrolysis cell, it's basically just allowed to bubble up into a chamber (it only bubbles up from the negative electrode), and then pressurized from there.

AjayJain73 wrote: 6. When I added Cobalt Nitrate in the last before the voltage stabilzed, the voltage reading on the voltmeter was 1.94v but the voltage reading in the clear Phosphate Buffer solution after that was 2.02V. Why the voltage reading increased after putting the electrodes in clear Phosphate Buffer solution?

Hmmm... I can't explain that (mostly because I'm not much of a chemist, I'm afraid). Did you rinse off the electrodes before moving them to the buffer? If not, you may be getting a little bit of a reaction from the residual cobalt.

Are we using Nickel Metal Strip for both Anode and Cathode or did I mistaken? If so, why are we only using Nickel ?