Submitted on 4 June 2009
What is the osmolarity of 8.4% NaHCO3 solution? (Hint: Molecular weight of NaHCO3 is 84g)
A. 84 mOsmo/L
B. 1000 mOsmo/L
C. 2000 mOsmo/L
D. 840 mOsmo/L
Answer: C
Osmolarity is a measure of the solute concentration, defined as the number of osmoles of solute (i.e. moles of solute particles) per litre of solution. The osmoles include the number of particles that dissociate, e.g. Ionic compound like NaCl has 2 osmoles, non-ionic compound like glucose forms only 1 osmole.
8.4% means 8.4g/100ml, i.e. 84g/1000ml
since the MW of NaHCO3 is 84g, there are 1Mol in 1000ml, i.e. 1000 mmol/L
As NaHCO3 fully dissociates into 2 osmoles, there are therefore 2000 mOsmo in 1 L solution of 8.4% NaHCO3.