How does one conceptually understand this experiment for substances, like sucrose, which increase surface tension with concentration? In that case, one is finding the surface deficiency, correct? If one uses this same analysis with sucrose, I assume you could still find an area per molecule. However, that area per molecule would be negative. What would that mean physically? Great stuff, by the way.
Great question! The surface excess (Gamma) can be thought of as the difference between density of the surfactant at the surface, and the density of the surfactant in the bulk. (In both cases, by density I mean two-dimensional density in mol per square meter.) For many surfactants, the surface density is much larger than the bulk density, and so the bulk density can be neglected. This makes the surface density and the surface excess approximately equal. However, for compounds that are strong anti-surfactants, the reverse will be true: the bulk density will be much greater than the surface density, and so the surface density can be neglected. This makes the surface excess approximately equal to the negative of the bulk density. Finally, note that if the surface and bulk densities are similar in magnitude, we can't approximate either of them with the surface excess.
This may be an obvious question, but how is the slope of such a graph calculated. And should I take the whole graph to calculate the slope, or only the part of the graph that decreases. I was thinking of using the slope function in excel, but still don't know what range to take.
Not in this case since he's calculating surface tension/ln concentration. It would be as you say if it was just concentration, the ln part gets rid of your units.
Man you are great, that is sooo great piece of help to learn for my exams! Thank you!
Tomasz Ratajczyk for me too!!!
How does one conceptually understand this experiment for substances, like sucrose, which increase surface tension with concentration? In that case, one is finding the surface deficiency, correct? If one uses this same analysis with sucrose, I assume you could still find an area per molecule. However, that area per molecule would be negative. What would that mean physically? Great stuff, by the way.
Great question! The surface excess (Gamma) can be thought of as the difference between density of the surfactant at the surface, and the density of the surfactant in the bulk. (In both cases, by density I mean two-dimensional density in mol per square meter.)
For many surfactants, the surface density is much larger than the bulk density, and so the bulk density can be neglected. This makes the surface density and the surface excess approximately equal.
However, for compounds that are strong anti-surfactants, the reverse will be true: the bulk density will be much greater than the surface density, and so the surface density can be neglected. This makes the surface excess approximately equal to the negative of the bulk density.
Finally, note that if the surface and bulk densities are similar in magnitude, we can't approximate either of them with the surface excess.
Thank you, John. This is very helpful.
3:59 "... to the negative sex" you slipped that one in, didn't you
Great work. I've been having trouble understanding surface excess and explaining it to my engineering students. This will help me a great deal.
This may be an obvious question, but how is the slope of such a graph calculated. And should I take the whole graph to calculate the slope, or only the part of the graph that decreases. I was thinking of using the slope function in excel, but still don't know what range to take.
Thank you. Very helpful
THANKS DUDE YOU HELP ME SO MUCH
Why are the units for the slope in mN/m? Shouldn't they be in mN/m per M?
Not in this case since he's calculating surface tension/ln concentration. It would be as you say if it was just concentration, the ln part gets rid of your units.
Hello what happens if the solute dissociate ? such as NaCl, KCl solutions.
Thank you for this. Very helpful🙏🙏
Hye..
why I calculate I get 415.28 A square?
Thnk you soo much ❤️❤️❤️❤️
A big thanks... :)
Thank you!!!
:)
I love you