Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: sorincosofret on 07/08/2008 13:48:38
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A 10 euro (overrated) Daniel cell experiment
Materials for the experiment:
Cu and Zn metals strips;
CuSO4 and ZnSO4 as 1M solutions;
Salt bridges made after the following recipe:
3 g of agar-agar are boiled in 250 ml deionised water.
The entire volume is divided in four and to every quarter is added:
1) NaOH 0,1M or higher concentrations - aprox 5 ml
2) CaCl2 about 0.1 g
3) CaCl2 about 2 g.
4) CaCl2 about 2 g.
In this way 4 different salt bridges are made.
4 tubes of PVC (or another material) are curved in a U shape and filled with up presented solution. At the ends of the tube some glass wool is fitted as appear in down figures.
The tubes are leaved to cool down and after the gel apparition, the bridge is ready.
The 4th bridge is a repetition of 3rd bridge, but instead of glass wool at the ends of the tube, 2 pieces of graphite recovered from some old carbon zinc battery are used as presented in down figures.
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The experiment is designed to check the movement of the ions from bridge to solution.
First, the diluted CaCl2 bridge is used. The potential registered is about 1,1 V. In solution there is no confirmation of a precipitate apparition after 2 hour of working with a multimeter connected to it.
Another cell is formed with concentrated CaCl2 solution. The potential registered is about 1,15 V. In solution there is no confirmation of a precipitate apparition after 2 hour of working with a multimeter connected to it.
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The third cell is formed with a NaOH bridge. Before bridge insertion and after 2 hours of cell working the pH is measured with pH paper. Before bridge insertion the pH of ZnSO4 was approx 5 and the pH of CuSO4 was about 9. After two hours the same values were registered.
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The 4th cell is formed with a bridge having a ,,mixed” conduction. The graphite is an electronic conductor and the gel is an ionic conductor (according to actual classification). The contact between bridge and CuSO4 and ZnSO4 solutions is made only by graphite portion of the bridge. The potential registered is about 0,8 V.
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How can be interpreted these results?
If an ion circulation is necessary for cell working, the calcium ion should pass in sulfate solution. Similarly chloride ion should pass in the other baker. A reaction between sulfate and Ca should occur and a precipitate should appear. In the first case the concentration of CaCl2 is to low to arrive to a product solubility of CaSO4.
How is cell working in this case?
In case of concentrated CaCl2 bridge, in the CuSO4 baker should appear a precipitate of CaSO4. The quantity of Cl and Ca gained by every solution can be determined analytically. After two hours of cell working a small quantity of Cl can be put in evidence using AgNO3 as reagent. The CaSO4 precipitate does not appear. The diffusion of CaCl2 from the bridge in solution is due to the Fick diffusion and not due to an electrochemical transport.
In the third case the pH of the solution should appear basic in a Zn compartment, and also Zn(OH)2 should precipitate, which is not the case.
In the same time the logical aspect of problem is not solved.
For every atom of Zn which passes in solution, two hydroxyls ions should come from bridge. In the bridge there are not enough ions (5 ml of NaOH 0.1M diluted to 75 ml agar agar solution) to satisfy this necessity.
Do ions circulate from a baker to another?
In the fourth cell is completely inexplicable how an ion can pass through a graphite material.
I post only the experiments in order to avoid to be moved again at ,,new theory” department.
I leave the explanation of these experiments to ,,high authority” presents on the forum.
Soon other experiments will be available.
The proposed interpretation will be detailed in Chemistry principle and Electricity related book
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"In the fourth cell is completely inexplicable how an ion can pass through a graphite material. "
Sorin can't explain this, but I can. He has 3 cells in series, he just hasn't noticed.
There's nothing unexplained about the other observations- for the most part it's down to the slow formation of precipitates in viscous materials like agar. It seems he just doesn'yt understand the basic science.
That leads me to wonder why anyone would want to buy his book.
BTW, does this site have a policy on blatant advertising?
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I don't think the book is ready for publication, yet. One or two small things to sort out first, I suspect.