If the molarity is known one can calculate osmolarity using the simple formula t

Question

If the molarity is known one can calculate osmolarity using the simple formula that follows:   

If the osmolarity of a 0.3M solution of KCl needed to be determined one could use the above formula to solve for osmolarity.  Now work with the following questions.        

1)    What is the osmolarity of a 3.5 molar solution of NaCl?

2)    What is the osmolarity of a 1.5 molar solution of glucose?

3)    Once you have computed the osmolarity for the above two questions determine which has the greater ability to influence fluid movement.

Explanation / Answer

PART (1): NaCl creates TWO solute particles when in solution.

So, its Osmolarity = (3.5M) ( 2) = 7.0 Osmolarity units.

PART (2):   glucose does not ionize in solution, so it remains as ONE solute particle in solution. So, its Osmolarity = (1.5M)(1) = 1.5 Osmolarity units.  

The NaCl solution has a much larger Osmolarity than glucose, so NaCl will have the greater ability to influence fluid movement.

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