My video on the Generon nitrogen membrane filter received some good comments, and one of them sent me on a path of calculation that I'm having a bit
of trouble on. I wrote up my findings on my blog, here: http://thehomescientist.blogspot.com/2018/03/generon-filter-...
But I'll give a summary here. I'm burning ethanol in a closed container to use up the oxygen, as a way of measuring the percent of oxygen in the gas
in the container. It was pointed out that ethanol produces 2 moles of CO2 for every 3 moles of O2, which in retrospect is obvious:
C2H5OH + 3O2 == 2CO2 + 3H2O
My goal is to find out the solubility of carbon dioxide in water, to determine if this affected my results or if it all just dissolved. I found a
chart on CO2 solubility here:
And in my linked post I took the 1.5g/kg at ~25C value and called it a day. However the site also mentions "Note that for gases in combination
with other gases - like oxygen in air - the partial pressure of the gas must be used. Example - in air with normal composition oxygen counts for
approximate 20% of the total pressure."
I tried finding a chart of solubility that also included pressure, but came up dry. Can anyone point me to a reference? It would have to be for fairly
low partial pressures; in one experiment I produced 88.2mL of the gas in a 630mL volume, yielding a partial pressure of 14 kPa.
Or is there a way to calculate solubility based on the pure gas chart above? Surely it's not as simple as taking a % of the charted values?Magpie - 22-3-2018 at 12:42
Knowing next to nothing, my first instinct is to ask if burning it in ethanol is the simplest method of ascertaining the O2 concentration.
Mumble mumble.MrHomeScientist - 23-3-2018 at 08:43
Quote:
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure
of that gas in equilibrium with that liquid.
Huh, so it really is that simple? That graph above is for atmospheric pressure (101 kPa), so it would be
(1.5 g/kg) / (101kPa) = (x) / (14kPa)
x = 0.21 g/kg
Knowing next to nothing, my first instinct is to ask if burning it in ethanol is the simplest method of ascertaining the O2 concentration.
Mumble mumble.
It seemed simple at the time. The other option was to rust fine steel wool in the container, but that takes a very long time. I tried it with a hand
warmer pack, since that contains iron powder and works by rusting quickly, but that didn't give very good results over a 24 hour period. I had to
abandon it because I needed to return the filter. Perhaps I should have planned better...Magpie - 23-3-2018 at 18:44
I used Henry's Law to calculate the the concentration of CO2 in the water assuming the following partial pressure over the water:
