Osmolarity

Question 1

Average osmolarity of the human body

Answer 1

290 mOsm

Question 2

o Osmolarity =

Answer 2

g x [C]
 g = dissociation constant (how many particles the solute will dissociate into).
 g=1 if the solute doesn’t dissociate.
 g>1 if the solute dissociates. Remember that most solutes don’t dissociate completely, so g will have a decimal place with it.
 [C] = the molar concentration of the substance

Question 3

 Osmotic pressure =

Answer 3

g[C] x σRT
 σ - reflection coefficient, a measure of permeability
 If σ=0, the solute is completely permeable and osmosis will NOT occur because the solute will diffuse.
 If σ = 1, the solute is completely impermeable and osmosis must occur.

Question 4

• Estimated Osmolality =

Answer 4

(2x [Na]) + ([glucose]/18) + ([BUN}/2.8)