Question

What is the osmolarity of a solution containing 0.2 M CaCl2 and 50 mM glucose?
A. 25 mOsm/l
B. 700 mOsm/l
C. 250 mOsm/l
D. 650 mOsm/l

Answer 1

CaCl2 = 0.2 M = 0.2 mol / L

Glucose = 50 mM = 50 x 10-3 M = 50 x 10-3 mol / L

Osmolarity = osmol / L

CaCl2 osmolarity = 0.2 mol /L 3 Osm/ mol ( as the molecule breaks in 3 ions - 1 Ca and 2 Cl)

CaCl2 osmolarity = 0.6 Osm/L = 600 mOsm/L

Glucose Osmolarity = 50 x 10-3 mol/L x 1 Osm/mol ( as glucose is a monovalent compound)

Glucose osmolarity = 50 x 10-3 Osm/L = 50 mOsm/L

Total osmolarity = Osmolarity of Calcium Chloride + Osmolarity of Glucose

Total Osmolarity = 600 + 50 = 650 mOsm/L