Can someone explain what happen to a liquid or a solid (powder) product when it is diluted or dissoluted ? What are the importances of temperature and
pressure.
Why an immobilized solution of sulfuric acid (during a long time) don't let appear to level, one of water and one of sulfuric acid.Quantum - 27-8-2004 at 08:51
Are you asking why don't water and H2SO4 form 2 seprate layers!? They disolve into each other sometimes quite exothermicly as I was reminded of
the other day by my ruined shirt. When a solute disoves into a solvent they form a compleatly homo mix with the indavidiual ions(or mols) so small
they can't even effect light like a colloid could.unionised - 27-8-2004 at 12:38
I think he is asking two things, one is "can you help me with my homework?"
and the other is why they don't un-mix to some degree. The acid is denser so it should sink; the question is what stops this effect being
noticable?JohnWW - 27-8-2004 at 14:56
If one carefully pours a layer of H2O on top of concentrated H2SO4, without disturbing the latter, the mixing of the two would be slight, because of
the much greater density and viscosity of H2SO4 Diffusion of the layers into each other due to Brownian motion would proceed slowly with liberation of
heat. Only when the two layers are physically disturbed by mixing would the liberation of heat become substantial.
Mixing of two dissimilar liquids, as in chemical reactors, is an area of hydrodynamics of great importance to chemical engineering - see the early
pages of Perry part 19, which also covers design of mixing equipment.
John W.
diffusion
Magpie - 27-8-2004 at 18:30
I'd like to describe a related problem reported to me on my job for which I never heard much of an explanation:
We had a lot of ducting for radioactive gas and particulate control in my nuclear industry work. Every so often someone would tell me that the
ducting was contaminated significantly upstream of the source. This is easily detectable with monitoring equipment often without even opening up the
duct. The only explanation I could come up with was that diffusion was taking place in the stagnant boundary layer next to the duct wall. Other than
accidental backflows, do other board members have any other explanations for this phenomenon? Has this happened to you?vulture - 28-8-2004 at 02:22
I'm not sure if you ever had fluid flow properties magpie, but this is pretty normal for non turbulent flow. In a straight walled pipe the flow
evolves to a parabolic velocity profile and the speed at the wall edges becomes virtually zero.
Quote:
If one carefully pours a layer of H2O on top of concentrated H2SO4, without disturbing the latter, the mixing of the two would be slight, because of
the much greater density and viscosity of H2SO4
This is an EXTREMELY BAD idea. The mixture will rapidly boil at the boundary layer and geiser in your face. This is why one should never pour H2O on
concentrated H2SO4.JohnWW - 28-8-2004 at 05:27
Of course, boiling would be a form of induced mixing, and this mixing of the layers would itself increase the boiling. But, noting also that diffusion
increases with temperature, this should not happen if the two liquids were sufficiently cooled to begin with - perhaps using frozen H2SO4 - and kept
cooled, with the water poured dropwise or finely sprayed, very slowly, on top.
John W.vulture - 28-8-2004 at 07:57
Quote:
perhaps using frozen H2SO4 - and kept cooled, with the water poured dropwise or finely sprayed, very slowly, on top.
Won't work, because the freezing point of H2SO4/water mixtures is lower than pure H2SO4. Your blob of H2SO4 will melt and cool down a bit. Then
the trouble starts. You now have a very intimate mixture of liquid H2SO4 and H2O in contact....Magpie - 28-8-2004 at 12:12
Vulture, knowing that you are a gentleman, I will assume that you were sincere in wondering if I had ever taken a fluid mechanics course. Certainly I
have, and with top grade. I can't imagine, even today, that you could receive a degree in chemical engineering without that course.
I feel that having taken this course was what enabled me to formulate an explanation to what would appear impossible to a layman - flow in a counter
direction to the bulk flow.
I posed the question only to see if others had observed this same phenomenon.
Whoopsie
vulture - 29-8-2004 at 00:59
Sorry bout that. I realize now it was maybe a bit insulting.
I haven't observed the phenomenon myself (maybe I should hike down the chimney one day ) but our chemical engineering prof has beaten us silly with it.Magpie - 2-9-2004 at 10:52
Vulture,
I think I overreacted to your comment. It is just that I worked so hard for that degree! I'm sure you understand.
I think your professor is doing well to pound in the boundary layer concept. I think it is important, and not well understood by most.
