What Is the Molarity of an Isotonic Saline Solution?

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SUMMARY

The molarity of an isotonic saline solution, specifically sodium chloride (NaCl) in water, must match the osmotic pressure of blood, which is 7.7 atm at 25°C. The relevant equation for calculating osmotic pressure is π = iMRT, where π represents osmotic pressure, M is molarity, R is the universal gas constant, and T is temperature in Kelvin. For NaCl, the van't Hoff factor (i) is 2, as it dissociates into two ions: sodium (Na+) and chloride (Cl-). Therefore, to find the molarity of an isotonic saline solution, one must substitute i with 2 in the equation.

PREREQUISITES
  • Understanding of osmotic pressure and its significance in biological systems.
  • Familiarity with the van't Hoff factor and its application in colligative properties.
  • Knowledge of the ideal gas law and its constants, particularly the universal gas constant (R).
  • Basic chemistry concepts regarding electrolytes and their dissociation in solution.
NEXT STEPS
  • Calculate the molarity of an isotonic saline solution using the equation π = iMRT.
  • Explore the implications of using different electrolytes in intravenous solutions.
  • Research the effects of osmotic pressure on cellular functions and fluid balance.
  • Study the van't Hoff factor in detail and its role in other colligative properties.
USEFUL FOR

Students in chemistry or biology, healthcare professionals involved in intravenous therapy, and anyone interested in the physiological effects of saline solutions.

Jeann25
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Aqueous solutions introduced into the bloodstream by injection must have the same osmotic pressure as blood; that is, they must be "isotonic" with blood. At 25C, the average osmotic pressure of blood is 7.7 atm. What is the molarity of an isotonic saline solution (NaCl in H2O)? Recall that NaCl is an electrolyte; assume complete conversion to Na and Cl ions.

The equation I have for osmosis is π=MRT (π=pressure, M=molarity, R=constant, T=temperature), but in the text it says this is for nonelectrolytes. I'm not sure where to go with this.
 
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Try looking into something called the van't Hoff factor.
 
The equation you gave can be converted to the osmosis equation for associating/dissociating solutes by multiplying the RHS with a factor 'i' (Also Called the Van't Hoff Factor)

So it becomes

Pi=iMRT

i is a factor defined as the number of particles after association/dissocation divided by the number of particles before it. One particle of NaCl Dissociates into two particles, The Sodium Ion and the Chloride Ion, so van't hoff factor for it is 2. replace i by 2 and proceed as usual.
 

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