Jose
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electrolytic production of ethane
There was a member who did an experiment on producing ethane from an acidified solution of sodium acetate. I want to know what voltage was used for
that process?
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WGTR
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That member was probably woelen.
The more important thing is to learn how to identify your products. Carbon dioxide is absorbed by shaking in a sealed syringe with sodium hydroxide
solution. Oxygen is absorbed the same way with acidified cuprous chloride. Ethane is left behind, and is flammable. Putting a needle on the
syringe, it's possible to produce a small flame.
It has been many years since I did this experiment, but the highlights that I remember where that the voltage needs to be high, even 10 volts or so,
to improve the selectivity towards ethane production. The power is pulsed on and off in order to lower the average current, to keep the solution from
warming up. The solution temperature is ideally kept cold on an ice bath, to raise the overvoltage for oxygen production. The anode is graphite to
also raise the oxygen overvoltage. This wasn't some kind of efficient production method, but I made some small amounts of ethane with it. I was even
able to weight the gas in a dry syringe, on a microbalance.
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wg48
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Quote: Originally posted by Jose  | | There was a member who did an experiment on producing ethane from an acidified solution of sodium acetate. I want to know what voltage was used for
that process? |
From memory woelen used a 12V or 15V DC supply with a series resistor to limit the current.
Here is an electrolytic method using AC and unfortunately platinum electrodes but up to 60% efficiency (see note for the basis).
Attachment: prod-ethain-electro-shipley1939 (1).pdf (323kB)
This file has been downloaded 279 times
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Tsjerk
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How do you do that?
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WGTR
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There are two answers, a short one, and a long one.
The short answer is, "Very carefully."
The long answer is: I massed several gasses, air, oxygen, nitrogen, carbon dioxide, hydrogen, methane, and ethane. With the exception of the
nitrogen (which is very dry in our lab), the gasses had to be dried first. I did this by freezing the sealed syringe full of gas in a freezer. While
the syringe was still cold, I pushed the gas from this syringe into a new, very dry and clean syringe, thereby producing a syringe full of fairly
well-dried whatever gas. It was necessary, of course, to wait some hours to ensure that the gas was now at room temperature. The plunger was worked
in and out a bit to make sure that the gas inside was at 1 atm, and then the syringe was massed. Since the syringe is much heavier than the gas that
it contains, the contribution of the gas to the overall mass was down into the noise. For this reason it was necessary to make a couple dozen
measurements, and then average the results together. It was crucial to do each measurement the exact same way every time. A single added fingerprint
on the syringe could introduce error into the measurement.
I was able to distinguish between all of the gasses (except for a couple, I think, that had the same mass), and the differences between each one
matched up fairly well with Avogadro's gas law, with some small error of course.
[Edited on 11-8-2018 by WGTR]
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Tsjerk
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I knew there would be a nice answer too that question. Nice work, I would probably have believed the literature or calculated densities...
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kulep
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Aren't you just measuring the difference between the gas mass and that of the atmosphere per Archimedes' principle? You would need to assume
atmosphere's density according to temperature and humidity.
Think about this, how would you measure the mass of a syringe full of gas underwater?
[Edited on 8-11-2018 by kulep]
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phlogiston
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Here is a link to woelen's page describing the experiment:
http://woelen.homescience.net/science/chem/exps/precision_el...
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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WGTR
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| Quote: Originally posted by kulep | Aren't you just measuring the difference between the gas mass and that of the atmosphere per Archimedes' principle? You would need to assume
atmosphere's density according to temperature and humidity.
Think about this, how would you measure the mass of a syringe full of gas underwater?
[Edited on 8-11-2018 by kulep] |
Well it's been several years, but from what I remember, I was just measuring the difference in mass between a known gas sample and an "unknown" one.
So long as the measurements are done at the same time, atmospheric conditions should cancel out, right? At least I hope they do. If measurements
were done on different days, I could see the necessity for accounting for atmospheric variations. Maybe the measurements would have been even more
accurate had I accounted for those things.
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