Question

What is the osmolarity (Osm) of a quarter-normal 0.22 %(m/v)NaCl solution?

Answer 1

Osmolarity is dependent upon the number of impermeant molecules molecules in a solution,not on the identity of the molecules.

For example,a 1M solution of a nonionizing substance such as glucose is a one Osmolar solution; a 1M solution of NaCl=2 Osm ; and 1M solution of Na2So4=3 Osm.

A quarter normal NaCl means 0.22% NaCl solution.

w/v % = 0.22%

Molarity of NaCl solution = (w/v %) * 10 / GMW of NaCl

                                    = 0.22 * 10 / 58.44

                                    = 2.2 / 58.44

Molarity of NaCl solution = 0.038 M

Osmolarity = 2 * Molarity of NaCl

                 = 2 * 0.038

                 = 0.076 Osm

Osmolarity of a quarter normal NaCl solution = 0.076 Osm