Question

Intravenous, or IV solutions used in medicine must exert the same osmotic pressure as blood to prevent a net flow of water into or out of the blood cells. The proper concentration for an intravenous NaCl solution is 0.90 g NaCl per 100. mL of water (sometimes refered to as 0.90% m/v).

If the van\'t Hoff factor of NaCl is i = 1.8, what is the osmotic pressure of blood at body temperature, 37 °C?

Answer 1

Van\'t Hoff factor is a measurement of degree of dissociation or association of solute particles in solution. If α is degree of dissociation, i =α+1= 1 means no dissociation, i = 2 means 100% dissociation whereas i<1 means association of the solute molecules. More the no of solute molecules in the solution more will be the change of colligative properties.

In terms of osmotic pressure, i = π_actual/π_calculated

π_calculatedis the value of π (osmotic pressure) when i is assumed to be 1, i.e., when solute particles do not dissociate or associate to change the overall no of solute particles in the solution.

0.90 g NaCl per 100. mL of water

= 0.9*10/58.5 moles of NaCl per 1 liter of water

= 0.1538 (M) solution

i = π_actual/π_calculated = π_actual/CRT .......(where C = concentration of solution in molarity)

π_actual = i*CRT = 1.8 * 0.1538 mol.lit^-1 * 0.082 lit.atm.mol^-1.K^-1 * 310 K

= 7.039 atm

So, osmotic pressure of blood at body temperature, 37 °C = 7.039 atm