Sciencemadness Discussion Board

electrolytic production of ethane

Jose - 7-11-2018 at 08:13

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?

WGTR - 7-11-2018 at 16:28

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.

wg48 - 8-11-2018 at 05:08

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 281 times

Tsjerk - 8-11-2018 at 06:04

Quote: Originally posted by WGTR  
I was even able to weight the gas in a dry syringe, on a microbalance.



How do you do that?

WGTR - 8-11-2018 at 08:27

Quote: Originally posted by Tsjerk  
How do you do that?


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]

Tsjerk - 8-11-2018 at 09:24

I knew there would be a nice answer too that question. Nice work, I would probably have believed the literature or calculated densities...

kulep - 8-11-2018 at 11:12

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]

phlogiston - 8-11-2018 at 11:28

Here is a link to woelen's page describing the experiment:

http://woelen.homescience.net/science/chem/exps/precision_el...

WGTR - 8-11-2018 at 13:42

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.