Saline is a solution that contains a certain amount of NaCl and is designed to have the same osmotic pressure as normal blood cells. Doctors often give saline to patients who have lost blood. Which of the following explains why glucose of the same molality cannot attain the same effect as saline?

At the same molality, osmotic pressure depends on how many dissolved particles are present. NaCl ionizes into sodium and chloride ions, producing about two particles per formula unit, while glucose dissolves as individual molecules and produces one particle per molecule. Thus, glucose of the same molality has a lower osmotic pressure than saline, so it will not have the same effect. The correct choice is B, “Each formula unit of NaCl will give two particles … but each molecule of glucose … only one particle.”

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