User:Andy Maloney/Notebook/Lab Notebook of Andy Maloney/2009/10/03/The osmotic pressure of concentrated solutions and the laws of the perfect solution

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These are my thoughts and ideas on this paper. Before you take my word, please read the paper. If you have comments or suggestions, please post them to the talk page.


The osmotic pressure of concentrated solutions, and the laws of the perfect solution


Very informative. Lewis tends to trash other scientists in the paper but, I suppose that was a different time when it was written.

At any rate, he goes over how to understand and relate osmotic pressure to some simple physical ideas that are easy for a physicist to grasp. Namely that, osmotic pressure is related to the ratio of vapor pressures for the pure solvent and the solvent plus solute.

He also describes osmotic pressure in the language of heat of dilution. I believe that heat of dilution is nothing more than the entropy of mixing. I think they are the same because as you dilute a solute in solution, the solvent has more space to occupy. If you increase the space the solvent occupies, then you increase it's entropy. As entropy increases, so does heat and thus this is why I think they are the same.

Very cool. Also in the process of reading this paper, I relearned that there is an inverse relationship between vapor pressure and boiling temperature. As a solution's vapor pressure decreases, it's boiling point increases. This is clearly understood by boiling water for your noodles. If you salt the water (as you should since you are making noodles and you want to season them properly) the boiling point of the water increases and thus it's vapor pressure decreases.

This is without a doubt a horrible analogy since I am interfacing salted water with the atmosphere, but it is fun to think about because it involves food. If you imagine the surface of the water as a semi-permeable membrane, then the water in your pot has an osmotic pressure above the "osmotic pressure" it would have without the salt. So, as you decrease a solution's vapor pressure, you increase it's osmotic pressure. Very cool.