What is osmotic pressure, and what is it dependent on?

Osmotic pressure is the pressure that needs to be applied to one side of a semi-permeable membrane to prevent solvent flow across the membrane into the more concentrated side, and is given by:

#Pi = iMRT#,

where:

• #i# is the van't Hoff factor for the solute(s), i.e. the effective number of particles in solution per formula unit.
• #M# is the solution concentration in... well, #"mol/L"#, molarity, #"M"#.
• #Pi# is the osmotic pressure in #"atm"#, if #R# is the universal gas constant in #"L"cdot"mol/atm"cdot "K"#.
• #T# is temperature in #"K"#, as usual.

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Thus, osmotic pressure is dependent on

• the electrolytic features of the solute (the stronger the electrolyte, the more particles per formula unit, and thus the higher the #Pi# needed to stop a larger number of solute particles from sucking up the solvent)
• the concentration of the solution on one side of the membrane (the higher it is, the greater the #Pi# needed to stop a higher concentration of solute from sucking up the solvent)
• the temperature of the solution (the higher it is, the greater #Pi# is to stop the faster solvent flow in warmer environments)

These are all direct proportionalities, i.e. as #Tuarr#, #Piuarr#, etc.