Osmolarity (or if working in molal rather than molar concentrations, osmolality)

Question

Osmolarity (or if working in molal rather than molar concentrations, osmolality) is a quantity that refers to the concentration of dissolved species in a solution. In your body, normal osmolarity of blood serum is just under 0.3 molar. Because cell membranes are permeable to water, normally the osmolarity of intracellular fluid is approximately equal to that of extracellular fluid (though the intracellular and extracellular composition in terms of specific ions and proteins is quite different). As an aside, measurement of osmolarity of serum is an important clinical test used to check for dehydration or other imbalances of water and electrolytes.

In class we briefly discussed osmotic processes, and in the lecture notes a formula was provided for osmotic pressure as a function of solute concentration (Topic 5, Equation (5.30) including text before and after). The solute discussed in the notes was sucrose, but we can consider the same formula to apply for other solutes. Using this formula, calculate the osmotic pressure associated with 0.3 molar concentration of osmolytic particles (ions, proteins, or other dissolved particles) in contact with pure water through a semi-permeable membrane at physiological temperature of 310 K. Express your results in atmospheres of pressure (1 atmosphere of pressure is 1.0x105 Pascal, where 1 Pascal is a Newton/m2).

Osmolarity (or if working in molal rather than molar concentrations, osmolality) is a quantity that refers to the concentration of dissolved species in a solution. In your body, normal osmolarity of blood serum is just under 0.3 molar. Because cell membranes are permeable to water, normally the osmolarity of intracellular fluid is approximately equal to that of extracellular fluid (though the intracellular and extracellular composition in terms of specific ions and proteins is quite different). As an aside, measurement of osmolarity of serum is an important clinical test used to check for dehydration or other imbalances of water and electrolytes.

Explanation / Answer

Osmotic Pressure = MRT = [0.3 mol/ L] * [0.08206 L atm/ mol K] * [310K] = 7.63 atm, where M- molar concentration; R-ideal gas concentration & T-Temperature.

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