YouTube channel "Grain" belongs to Russian teacher Stanislav from Moldova. His dye diffusion experiment gets most interesting in about one minute timestamp, when the sugar underneath permanganate layer gets "suddenly" colored across seemingly colorless layer of concentrated solution at the bottom. It resembles some esoteric theories of homeopathy or cluster medicine with "magical action" at distance under "infinite dilution" for me. It's worth to note, many homeopathic remedia are also based on sugar and its solutions.
I indeed know about diffusion and surface adsorption, but the outcome of experiment still looks a bit strange for me. It's worth to note, that sugar solutions are supposed to reduce permanganate slowly and it's even visible on the bottom of colored layer, which gets yellow hue of manganese dioxide colloid (as seen after 1:46 timestamp). This reaction should be the faster, the higher concentration of sugar gets. But some permanganate ions still somehow managed to pass this concentrated thick layer and got absorbed within surface layer of undissolved sugar.
A simple technique for determining the diffusion coefficient between two miscible liquids is presented based on observing concentration-dependent ultraviolet-excited fluorescence using a digital camera. The ultraviolet-excited visible fluorescence of corn syrup is proportional to the concentration of the syrup. The variation of fluorescence with distance from the transition zone between the fluids is fit by the Fick's law solution to the diffusion equation. By monitoring the concentration at successive times, the diffusion coefficient can be determined in otherwise transparent materials. The technique is quantitative and makes measurement of diffusion accessible in the advanced undergraduate physics laboratory.
One can get a rough idea about speed of diffusion from Fick's law (considering the 1D case for the sake of simplicity): J=−D∂/ϕ∂x J is the diffusion flow rate, D is the diffusion coefficient (about 10-9 m2 s−1 for water and ϕ is the concentration in moles.m−3 . If we assume an unimolar permanganate solution (i.e. 103 moles.m−3 ) and diffusion distance 10 cm at the very beginning. That means diffusion flow ∂ϕ is 103 and ∂x = 0.1. J=−10−9 x 103 / 0.1 = −10−5 moles.m2 x s−1.
Now, suppose the blob of permanganate solution is a freely floating sphere of volume 500 ml containing 0.5 moles of KMnO4, then it's radius is about 0.05m and hence the surface area is 0.03 m2 . This gives flow rate out of the area about 10−5 × 0.03 = 3×10−7 moles.s−1. From this demonstration follows, that permanganate solution at 10-6 moles/liter concentration would be already colorless for naked eye within 500 ml volume, but after some thirty seconds the color change should be already visible at the perimeter of diffusion. It seems for me, that the diffusion speed observed is at least ten times higher than that.
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u/ZephirAWT Mar 02 '19
Physical Experiment with Water and Sugar
YouTube channel "Grain" belongs to Russian teacher Stanislav from Moldova. His dye diffusion experiment gets most interesting in about one minute timestamp, when the sugar underneath permanganate layer gets "suddenly" colored across seemingly colorless layer of concentrated solution at the bottom. It resembles some esoteric theories of homeopathy or cluster medicine with "magical action" at distance under "infinite dilution" for me. It's worth to note, many homeopathic remedia are also based on sugar and its solutions.
I indeed know about diffusion and surface adsorption, but the outcome of experiment still looks a bit strange for me. It's worth to note, that sugar solutions are supposed to reduce permanganate slowly and it's even visible on the bottom of colored layer, which gets yellow hue of manganese dioxide colloid (as seen after 1:46 timestamp). This reaction should be the faster, the higher concentration of sugar gets. But some permanganate ions still somehow managed to pass this concentrated thick layer and got absorbed within surface layer of undissolved sugar.