# Naked Science Forum

## Non Life Sciences => Chemistry => Topic started by: scientizscht on 24/02/2019 16:04:57

Title: What is the measure of the osmotic force induced by a substance?
Post by: scientizscht on 24/02/2019 16:04:57
What is the parameter that measures of the osmotic force induced by a substance?
I mean you have two substances, what expresses how much water each will drag through a semipermeable membrane?
Title: Re: What is the measure of the osmotic force induced by a substance?
Post by: chiralSPO on 24/02/2019 18:03:46
look up "colligative properties"
Title: Re: What is the measure of the osmotic force induced by a substance?
Post by: scientizscht on 24/02/2019 18:42:24
colligative properties

It doesn't help.
Is it osmolarity, osmolality?
Title: Re: What is the measure of the osmotic force induced by a substance?
Post by: chiralSPO on 24/02/2019 19:07:11
osmotic pressure is what gets measured.

Osmotic pressure is determined by mole fraction of non-water species in solution (proportional to molality).

For compounds that don't dissociate it is easy
For a given mass of water, osmotic pressure of one mole of ethanol = one mole of methanol = one mole of acetone = one mole of glucose (if you care about mass of solute, this will then vary by molar mass of the solute, so 32 g of methanol = 46 g of ethanol = 58 g of acetone = 180 g of glucose

For compounds that do dissociate, you have to account for how much they dissociate, and into how many species they do
one mole of ethanol < one mole of acetic acid < one mole of formic acid < one mole of hydrochloric acid < one mole of sulfuric acid < one mole of calcium chloride etc.