Question everything!

[Farrah Day]

The production of hydrogen and oxygen from water used to be a very simple experiment that we performed at school. Just like Faraday, we drew an electric current through water via two relatively inert electrodes submerged within the water and we get hydrogen evolving at the cathode and oxygen at the anode.  The collected hydrogen gas was always twice the volume of the collected oxygen gas, (because of course each water molecule consisted of two hydrogen atoms and only one oxygen atom) and the total amount of gases evolving were directly proportional to the electric current drawn through the water. It all seemed straightforward enough and indeed that was all we needed to know to get us through our exams.

At the time not many of us questioned what we were being taught, after all, we were being taught by qualified teachers - adults... we had no reason to question them. They must obviously know what they are talking about (I now know this to be a common misconception).  

It was about this time that I realised, that just like us pupils, teachers themselves had simply been taught what they were teaching us, and unless they themselves had asked more in-depth questions, then they really knew no more than we now did.

Even at 13, I had - and always have had - a very keen interest in science, so I was a little more knowledgeable on the subject than my fellow pupils were. And while everybody else accepted the above electrolysis experiment without question... I was somewhat confused.

I knew that hydrogen was the smallest element, having just a proton and an electron, and that oxygen was much larger with its eight protons, eight neutrons and eight electrons, so the resulting gas volumes baffled me.  Way back then I would have expected the oxygen gas to take up more space than the hydrogen gas, believing that it would require 16 tiny hydrogen atoms to take up the same volume as one oxygen atom.  Clearly this was not the case... why?

I asked my teacher at the time, why this was so. But it was obvious that he had never been faced with this question before, and as such had never given this any thought. Needless to say he did not know the answer.   I became renowned for asking questions that my teachers could not answer, and I'm sure some of them dreaded my appearance in their classes. My observations and questioning nature did however make someone take note and I was to receive the FK science award on the last day of secondary school.

Now all these years later, I'm still questioning. In fact I live by the motto:

Question everything. Sort the facts from the fiction. Verify the facts. Proceed with caution!

Nowhere does this logic have more merit than on these open source forums.

Science can be quite difficult to understand, indeed it can be quite complicated when the surface is scratched, and as such, many people with no relevant education find it a lot easier simply to dismiss the science and accept quackery. I see this all the time – it is clearly evident all the time. Quackery is often uncomplicated so immediately appeals to the ignorant - many of whom it would seem are also completely void of any common sense and quite happy to live out their lives in fantasy worlds.

The problem for me is that continually questioning things - particularly people and their claims - often does not go down overly well. I'm seen as disruptive and a trouble-maker simply for not accepting someone's word for something, and ultimately I'm banned from forums. My questioning and common sense approach to things often alienates me from other forum members, many of whom are unbelievably gullible, while being ignorant enough to happily jump on a bandwagon and blindly defend pseudoscience and gibberish.

However, this is not a popularity contest and irrelevant of how unpopular it may make you, it really is in everyone's best interest to:

Question everything. Sort the facts from the fiction. Verify the facts. Proceed with caution!

The answer to the gas volumes created by electrolysis can be put down to Avogadro's hypothesis, which states:

Equal volumes of different gases, at the same temperature and pressure, contain the same number of molecules.

This implies then that even though the hydrogen molecule has 1/16th the mass of an oxygen molecule, it takes up the same volume in space.

Which begs another question: If the hydrogen molecule is the same size in volume as the oxygen molecule - or any other gas molecule - how and why can it diffuse through a fabric that oxygen and other gases can not?  Or does it?

[MileHigh]

Farah:

The molecules are different in size, but that shouldn't be confused with how the two different gasses with the same number of molecules will fill up a container at the same temperature and pressure.

I am so rusty on this but I will give it a try.  First of all a gas is like when you break a rack of billiard balls and they start bouncing around, with the difference being that there are no pockets and the balls simply never stop bouncing off of each other and the sides, it goes on forever.  In physics these are called "perfectly elastic collisions."

The pressure on the walls of the container is proportional to the number of ball (or molecule) impacts per second.  Now you have the problem where the oxygen molecules are 16 times heavier than the hydrogen molecules.  The only way to explain the equal pressure would seem to be that the hydrogen molecules are moving much faster than the oxygen molecules resulting in more hits per second against the walls of the container and the average impact velocity is higher.  These two factors together result in the equivalent pressure as the case for oxygen molecules.

I could be wrong in some of the specifics but that's roughly what's going on.  Going back to the pool table analogy, oxygen would be like watching billiard balls bounce around endlessly and hydrogen would be like watching the same number of marbles bounce around endlessly but you notice that the marbles are doing this at a much higher average velocity with correspondingly more impacts per second against the sides.

Assuming all this is more or less true, it makes sense that you can have a membrane that hydrogen gas will be able to diffuse through but oxygen gas will not.

The proof in the pudding would be to look up the average velocity for oxygen gas molecules and for hydrogen gas molecules at "STP," the standard temperature and pressure.

MileHigh

[poynt99]

@ Farrah,



.99

[Room3327]

My questioning and common sense approach to things often alienates me from other forum members, many of whom are unbelievably gullible, while being ignorant enough to happily jump on a bandwagon and blindly defend pseudoscience and gibberish.

Hi Farrah,
I think you will find the questioning and common sense approach is alive and well at this forum.  I have been following your threads for a long time and I for one welcome you here, I doubt that you would ever be banned from here.

[Farrah Day]

Hi Room, thanks.

MH, good post and something I need to look into more. However, Avogadro's hypothesis (now incidentally, and for what it's worth, usually accepted as a law) suggests that the distance between the nucleus of the molecules of various gases is more or less equal. Which I take as suggesting that although the oxygen molecule has 16 times the mass of the hydrogen molecule, the outer electron shells of each are at about the same distance from the nucleus.

I recall I reading somewhere that even the heavy radioactive elements at some 200 times the mass of the hydrogen atom, are only 6 or 7 times greater in diameter, due to the greater attractive influence exerted on electrons by the more massive nucleus.

I'm aware that the movement and collisions of gases are what creates the pressure, but what you are saying suggests that every gas molecule of different mass would be moving at different velocities, which I suppose could be true. But then you would not expect every different gas the expand and contract in equal proportion to changes in temperature, which they appear to do.

All very interesting.

   

[aetherevarising]

hello Farrah,

I've just seen this thead.  You raise questions about the size of different atoms.  As I underatood it the more complex heavier atoms are also smaller.  Iron, for instance is much smaller than hydrogen.  The actual volume of the atom is inversely proportional to the size of the nucleus.  It's almost as if the atom's complexity increases so does it's volume diminish.  Theoretically therefore the Oxygen atom would be smaller not larger than the hydrogen atom.  I've just looked up the periodic table and don't see anything about atomic size - so I'm not sure where I learned this.  But I think it's right.

Regards,
Rosie