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Does 1M NaCl or 1M sucrose solution have a more negative solute potential?

I was thinking that for the same volume of solution, (eg 1 dm^3) there will be 2 mol of ions in NaCl solution and 1 mol of sucrose. However, there are more OH groups in sucrose that water can form hydration shells around.

So which solution has the more negative solute potential?

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  • $\begingroup$ I would say 1 M NaCl has lower solute potential. By the equation, solute potential is proportional to solute concentration. $\endgroup$ – canadianer Mar 15 '17 at 3:44
  • $\begingroup$ Yes, but how do we account for the fact that sucrose has more OH groups that water can form hydration shells around? Wouldn't that lower the solute potential to a greater extent than NaCl? There are more OH groups per mole of sucrose than there are ions per mole of NaCl. $\endgroup$ – Jonathan Smith Mar 15 '17 at 6:20
  • $\begingroup$ You are right. NaCl has a van't Hoff factor of 2. For simplicity you can assume sucrose as a simple solute and ignore macromolecular interactions. BTW, even sodium and chloride ions will have a hydration shell and its size depends on the surface charge density. $\endgroup$ – WYSIWYG Mar 15 '17 at 9:26
  • $\begingroup$ So, we assume that the hydration shells formed around Na+ and Cl- ions are bigger than those formed around sucrose (which we assume to have only one hydration shell formed around it)? $\endgroup$ – Jonathan Smith Mar 15 '17 at 9:34
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    $\begingroup$ Hydration shell is a totally different concept. I don't think it is a major factor in osmolarity. Osmolarity is a bulk property. $\endgroup$ – WYSIWYG Mar 15 '17 at 14:05

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