# How can I calculate osmolarity of dextrose?

##### 1 Answer
Aug 31, 2014

If the solution is sufficiently dilute, it will closely follow the ideal equation:

$P = c R T$

where P is the osmotic pressure (Pa), c is the concentration (moles per cubic meter), R is the universal gas constant (8.314 J/mol-K) and T is the absolute temperature (K).

Rearranging this expression allows you to calculate the concentration from a measured osmotic pressure (differential pressure across a semi-permeable membrane). You can then convert c to molarity (divide by ${10}^{6} \frac{L}{m} ^ 3$). The result will be very close to the molality if the solvent is water and the solution is dilute, because because 1 L of water has a mass very close to 1 kg.