Talk:Osmole (unit)

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Osmolarity and tonicity are not the same thing. Osmolarity pressure that solutes exert on either side of a membrane that allows only water to pass. In contrast, tonicity does not assume such a membrane. Thus, osmolarity is affected only by what solutes are put initially on both sides of the membrane, whereas tonicity is affected by both this and the possible flow of those solutes to the other side, which affects osmosis.

the articles should be linked, but merging them would be confusing.

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You are absolutely correct that osmolarity and tonicity are not the same thing. However, I believe you otherwise have your definitions for osmolarity and tonicity confused. Tonicity is in fact the phenomenon that refers to water movement exclusively, not osmolarity. Osmolarity takes into account the molecules that can't cross a membrane as well as those that can. I am not entirely sure though whether or not osmolarity absolutely demands the presence of a membrane. The majority of the definitions I've seen refer to the necessity that solutes exert oncotic pressure over a membrane. But it seems to me that simply having particles that would be oncotically active is enough to define a solution's osmolarity without the actual presence of a membrane. IE: A 1mM solution of sodium chloride represents a 2 mOsm/L solution, whether or not a membrane is present. I personally think an "Osmolarity vs. Tonicity" page should be created independent of "Osmolarity" and "Tonicity", to which both pages could link.

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