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It looks like you typed the same word twice: osmolarity and osmolarity. Maybe you meant to ask about the difference between:
- Osmolarity and osmolality?
If so, here’s the difference:
- Osmolarity is the number of osmoles of solute per liter of solution (Osm/L).
- Osmolality is the number of osmoles of solute per kilogram of solvent (Osm/kg).
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- Osmolarity depends on volume, which can change with temperature.
- Osmolality depends on mass, which is more stable and accurate, especially in clinical settings (like blood or urine tests).
Hossam Elgnainy Selected answer as best
1. Osmolarity (in mOsm/L):
Osmolarity = Molarity (mol/L) × Number of particles (n) × 1000
Example: For 0.9% NaCl (0.154 mol/L), which dissociates into 2 particles (Na⁺ and Cl⁻):
Osmolarity = 0.154 × 2 × 1000 = 308 mOsm/L
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2. Osmolality (in mOsm/kg):
Osmolality = Molality (mol/kg) × Number of particles (n)
In clinical settings (plasma osmolality is often estimated by):
Osmolality = (2 × [Na⁺]) + (Glucose / 18) + (BUN / 2.8)
All concentrations in mg/dL
Is the equation used to calculate osmolarity the same used to calculate osmolality ?