I would like to be tested / criticised on the following comment: in the beginning when demonstrating diffusion I do not think the experimentor demonstrated diffusion. I think she demonstrated brownian motion. And possibly not even that. The hot glas is in a thermal inequilibrium: the glas, the water, the room do not have the same temperature. The surface or top part of the hot water is cooler compared to the bottom part. Therefore it is likely that you have a circular convection current transporting energy from bottom to the top part. However, no circular current is seen. Thus the change in solute concentration is likely due to a combination between brownian and convection motion. A better experimental setup would be to have a heated chamber (can be acquired and biologist use it relatively often in their labequipment). In that setting, everything (water, glas, and room and also the solute substance) is in thermal equilibrium thus ruling out convection. My intuition tells me that transport via convection is much larger than brownian motion. Please comment on all this.
Hi @TobyOnTube, We appreciate your scientific curiosity! At the beginning of the video, we explained that diffusion is the movement of molecules from a high concentration to a low concentration. The purpose of the demonstration with the food colouring and the water at different temperatures is to show that the food colouring spread out more quickly in the warmer water than it did in the colder water. This was to explain that diffusion happens more quickly in warmer fluids. In the terms you are describing, we oversimplified in using the word diffusion having not considered convection or Brownian motion. Convection does explain the movement of the molecules in the fluid but it wasn’t the focus of the video. There may be other experimental setups that better demonstrate diffusion but again, that wasn’t our goal with the food colouring. The actual demonstration of diffusion was shown with the following two demonstrations to show diffusion through a semipermeable membrane using the dialysis tubing. Thank you for your question. We encourage you to go forth and carry out your own experimental methods to test your hypotheses!
Can't still believe that i got cured from Genital Herpes through herbal treatment from Dr david who I met through the internet, I actually couldn't believe it at first because it sounded impossible to me knowing how far I have gone just to get rid of it. Dr david send me his medicine which I took as instructed and here I am living a happy life once again, a big thanks to Dr david, I am sure there are many herbal doctors out there but Dr david did it for me, contact him davidherbalhome@gmail. com or also whats app him +2347042992115
Do you know ...that was awesome .for so many years a was perplexing In osmosis and diffusion .but today it is crystel clear .. Thanks a lot .God bless you..
Dr.S.S.Ahmed, from Hyderabad, India I really appreciate your efforts you made for this video..Its awsome. Will you please let me know the preperation on Semi Permeable Membrane too........
I am a student I really love this video the best explanation thanks for sharing this video it has helped me clearly to understand osmosis and diffusion thanks
Did anyone notice that she added 2 drops of red food colouring into the beaker of hot water and only 1 drop of blue food colouring into the beaker of cold water? And I wanna know if the amount of drops added matters
The Best way to go around this is to do diffusion experiments yourself. At least that is my plan. Demonstrating diffusion is not easy. The mean distance of a solute particle (food color) in a solvent (water) increases with the sqrt of time. This is one of the major results in Einstein's 1905 paper. This means that in the beginning things evolve (diffuse) rapidly but then slows down for larger and larger time periods. A complete mixing of the solute in the solvent could take days.
OK I think I figured out a mechanism for osmosis. Sal's explanation is kind of correct but doesn't quite express it right. The gist of it is that there is a net momentum vector for all the matter in the system that sits on the solute-solvent mixture side of the membrane. If you break the system down into two masses, the mass of water, and the mass of solute, we see that the mass of water's (solvent's) center of momentum movement is directly in the middle of the system over the membrane. However, when we look at the mass of solute's center of momentum, we see that it's in the middle of only the solute-solvent side. When you take the average of these two momentum vectors you get a net momentum vector that has a center somewhere between the two in physical space, so the tendency overall is for the water to move in the direction of the solute-solvent side toward the center of mass of the system. Another way to think of it is that the barrier imparts energy to the system only on the side in which it is capable of deflecting matter (solute side). The Brownian motion of the molecules is the driving energy of the movement of molecules in the system. Where does the energy come from from the Brownian motion? Well, perhaps there is some internal energy at the subatomic/nuclear level, but I suspect it's more driven by the addition of heat from the environment and the transfer of kinetic energy to the particles from the barrier and walls. If a molecule hits the membrane, it is accelerated in the opposite direction. Energy is imparted to the molecule from the wall, and the wall gains energy from the particle. With each exchange, some kinetic energy is lost due to friction. Because the membrane is, on net, only interacting with the solute particles, any kinetic energy that the solute particles lose to the membrane barrier is lost only in that side of the system, but not the other half. This would imply the overall kinetic energy of the solute-solvent system is less than the pure-solvent side, which would obviously lower the water pressure and thus move water, on net, into the solute-solvent mixture side. But, you might ask, osmosis is powerful enough, apparently, to work against gravity. This requires work, so energy LOSS doesn't seem to really explain how it can do work. Well, like I said, the Brownian motion of the particles is constant overall, so whatever inputs to the Brownian motion of the particles are, it must be the energy into these inputs that osmotic energy is driven by. It must be the case that the heat of the environment is going into one side of the system at a higher right than the other. I suppose that the solution must have the same temperature throughout on both sides of the membrane (does it? I suppose this could be measured). The order of energy seems to be: heat from environment --> Brownian motion of liquid particles (Kinetic Energy) --> energy lost to membrane barrier The energy lost to the barrier must be small compared to the increased input from the environment, otherwise you wouldn't be able to do work like elevate the solution against gravity. I would therefore speculate that the rate of heat intake in the system is greater on the solute-solvent side, because for the Brownian motion to remain constant, one needs an increased amount of energy to compensate for the energy lost at the membrane. So that's my hypothesis about osmotic mechanism. Any thoughts? The next question I have is: if this description is correct, does it imply that the total osmotic pressure is linked (proportional to) to the surface area of the membrane, or that the surface area of the membrane merely affects the rate of osmosis overall? Intuition at first tells me that the increased surface area of a membrane should increase the osmotic pressure overall, however as far as I know, the osmotic pressure is directly proportional to the solute concentration only, not the membrane surface area. This may imply that the surface area of the membrane only affects the rate of exchange, but not the overall osmotic pressure. This could be tested empirically by simply having two separate identical systems in terms of water mass, solute concentration on one side, and varying only the surface area of the membrane, and then measuring (1) what the rate of water movement is, and (2) what the overall end result is at equilibrium. If the rate varies but the end result is the same, then the membrane surface area doesn't affect the osmotic pressure. If the end result varies, then the osmotic pressure is proportional to the surface area of the membrane. As a secondary experiment, you could measure the temperature of the fluids and the rate of heat exchange on both sides of the membrane.
I am in 9th class from kashmir and that was my question why osmosis takes place through a semipermeable membra ne and i was thinking like what about diffusion now it's clear that diffusion occurs into a semipermeable membra ne.
what if you swap the sucrose with glucose solution? Glucose will diffuse out of the tubing while water molecules will just diffuses into the tubing until an equilibrium is reached , and so no change in the level of the solution in tubing and beaker, is that right?
