What is the osmolarity of 0.9% NaCI solution?

The osmolarity of 0.9% NaCI solution is approximately 300mC)sm\L, as can be shown in the following calculations:

100 mL of 0.9% NaCI solution contains 0.9g of the NaCI.

1L of 0.9% NaCI solution contains 9g of NaCI.

The molecular weight of NaCI is 58.5.

58.5g of NaCI is equal to 1 mole of NaCI.

9g of NaCI is equal to 1/58.5 x 9 moles, i.e. 0.154 mole or 154 millimoles.

However, each mole of NaCI releases 2 osmoles: one osmole of Na⁺ and one osmole of CI”. Thus, the osmolarity of 1 L of 0.9% NaCI solution is 308 mOsm (154 x 2).